block: move I/O request processing to block/io.c

The block.c file has grown to over 6000 lines.  It is time to split this
file so there are fewer conflicts and the code is easier to maintain.

Extract I/O request processing code:
 * Read
 * Write
 * Zero writes and making the image empty
 * Flush
 * Discard
 * ioctl
 * Tracked requests and queuing
 * Throttling and copy-on-read
 * Block status and allocated functions
 * Refreshing block limits
 * Reading/writing vmstate
 * qemu_blockalign() and friends

The patch simply moves code from block.c into block/io.c.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 2541 insertions, 1 deletions

diff --git a/block/Makefile.objs b/block/Makefile.objs
index 179e71d235..0d8c2a4ab6 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -9,7 +9,7 @@ block-obj-y += block-backend.o snapshot.o qapi.o
 block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
 block-obj-$(CONFIG_POSIX) += raw-posix.o
 block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
-block-obj-y += null.o mirror.o
+block-obj-y += null.o mirror.o io.o
 
 block-obj-y += nbd.o nbd-client.o sheepdog.o
 block-obj-$(CONFIG_LIBISCSI) += iscsi.o
diff --git a/block/io.c b/block/io.c
new file mode 100644
index 0000000000..1ce62c4fbc
--- /dev/null
+++ b/block/io.c
@@ -0,0 +1,2540 @@
+/*
+ * Block layer I/O functions
+ *
+ * Copyright (c) 2003 Fabrice Bellard
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "trace.h"
+#include "sysemu/qtest.h"
+#include "block/blockjob.h"
+#include "block/block_int.h"
+
+#define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */
+
+static BlockAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,
+        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
+        BlockCompletionFunc *cb, void *opaque);
+static BlockAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,
+        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
+        BlockCompletionFunc *cb, void *opaque);
+static int coroutine_fn bdrv_co_readv_em(BlockDriverState *bs,
+                                         int64_t sector_num, int nb_sectors,
+                                         QEMUIOVector *iov);
+static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
+                                         int64_t sector_num, int nb_sectors,
+                                         QEMUIOVector *iov);
+static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
+    int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
+    BdrvRequestFlags flags);
+static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
+    int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
+    BdrvRequestFlags flags);
+static BlockAIOCB *bdrv_co_aio_rw_vector(BlockDriverState *bs,
+                                         int64_t sector_num,
+                                         QEMUIOVector *qiov,
+                                         int nb_sectors,
+                                         BdrvRequestFlags flags,
+                                         BlockCompletionFunc *cb,
+                                         void *opaque,
+                                         bool is_write);
+static void coroutine_fn bdrv_co_do_rw(void *opaque);
+static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
+    int64_t sector_num, int nb_sectors, BdrvRequestFlags flags);
+
+/* throttling disk I/O limits */
+void bdrv_set_io_limits(BlockDriverState *bs,
+                        ThrottleConfig *cfg)
+{
+    int i;
+
+    throttle_config(&bs->throttle_state, cfg);
+
+    for (i = 0; i < 2; i++) {
+        qemu_co_enter_next(&bs->throttled_reqs[i]);
+    }
+}
+
+/* this function drain all the throttled IOs */
+static bool bdrv_start_throttled_reqs(BlockDriverState *bs)
+{
+    bool drained = false;
+    bool enabled = bs->io_limits_enabled;
+    int i;
+
+    bs->io_limits_enabled = false;
+
+    for (i = 0; i < 2; i++) {
+        while (qemu_co_enter_next(&bs->throttled_reqs[i])) {
+            drained = true;
+        }
+    }
+
+    bs->io_limits_enabled = enabled;
+
+    return drained;
+}
+
+void bdrv_io_limits_disable(BlockDriverState *bs)
+{
+    bs->io_limits_enabled = false;
+
+    bdrv_start_throttled_reqs(bs);
+
+    throttle_destroy(&bs->throttle_state);
+}
+
+static void bdrv_throttle_read_timer_cb(void *opaque)
+{
+    BlockDriverState *bs = opaque;
+    qemu_co_enter_next(&bs->throttled_reqs[0]);
+}
+
+static void bdrv_throttle_write_timer_cb(void *opaque)
+{
+    BlockDriverState *bs = opaque;
+    qemu_co_enter_next(&bs->throttled_reqs[1]);
+}
+
+/* should be called before bdrv_set_io_limits if a limit is set */
+void bdrv_io_limits_enable(BlockDriverState *bs)
+{
+    int clock_type = QEMU_CLOCK_REALTIME;
+
+    if (qtest_enabled()) {
+        /* For testing block IO throttling only */
+        clock_type = QEMU_CLOCK_VIRTUAL;
+    }
+    assert(!bs->io_limits_enabled);
+    throttle_init(&bs->throttle_state,
+                  bdrv_get_aio_context(bs),
+                  clock_type,
+                  bdrv_throttle_read_timer_cb,
+                  bdrv_throttle_write_timer_cb,
+                  bs);
+    bs->io_limits_enabled = true;
+}
+
+/* This function makes an IO wait if needed
+ *
+ * @nb_sectors: the number of sectors of the IO
+ * @is_write:   is the IO a write
+ */
+static void bdrv_io_limits_intercept(BlockDriverState *bs,
+                                     unsigned int bytes,
+                                     bool is_write)
+{
+    /* does this io must wait */
+    bool must_wait = throttle_schedule_timer(&bs->throttle_state, is_write);
+
+    /* if must wait or any request of this type throttled queue the IO */
+    if (must_wait ||
+        !qemu_co_queue_empty(&bs->throttled_reqs[is_write])) {
+        qemu_co_queue_wait(&bs->throttled_reqs[is_write]);
+    }
+
+    /* the IO will be executed, do the accounting */
+    throttle_account(&bs->throttle_state, is_write, bytes);
+
+
+    /* if the next request must wait -> do nothing */
+    if (throttle_schedule_timer(&bs->throttle_state, is_write)) {
+        return;
+    }
+
+    /* else queue next request for execution */
+    qemu_co_queue_next(&bs->throttled_reqs[is_write]);
+}
+
+void bdrv_setup_io_funcs(BlockDriver *bdrv)
+{
+    /* Block drivers without coroutine functions need emulation */
+    if (!bdrv->bdrv_co_readv) {
+        bdrv->bdrv_co_readv = bdrv_co_readv_em;
+        bdrv->bdrv_co_writev = bdrv_co_writev_em;
+
+        /* bdrv_co_readv_em()/brdv_co_writev_em() work in terms of aio, so if
+         * the block driver lacks aio we need to emulate that too.
+         */
+        if (!bdrv->bdrv_aio_readv) {
+            /* add AIO emulation layer */
+            bdrv->bdrv_aio_readv = bdrv_aio_readv_em;
+            bdrv->bdrv_aio_writev = bdrv_aio_writev_em;
+        }
+    }
+}
+
+void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+    BlockDriver *drv = bs->drv;
+    Error *local_err = NULL;
+
+    memset(&bs->bl, 0, sizeof(bs->bl));
+
+    if (!drv) {
+        return;
+    }
+
+    /* Take some limits from the children as a default */
+    if (bs->file) {
+        bdrv_refresh_limits(bs->file, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
+        bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
+        bs->bl.max_transfer_length = bs->file->bl.max_transfer_length;
+        bs->bl.opt_mem_alignment = bs->file->bl.opt_mem_alignment;
+    } else {
+        bs->bl.opt_mem_alignment = 512;
+    }
+
+    if (bs->backing_hd) {
+        bdrv_refresh_limits(bs->backing_hd, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
+        bs->bl.opt_transfer_length =
+            MAX(bs->bl.opt_transfer_length,
+                bs->backing_hd->bl.opt_transfer_length);
+        bs->bl.max_transfer_length =
+            MIN_NON_ZERO(bs->bl.max_transfer_length,
+                         bs->backing_hd->bl.max_transfer_length);
+        bs->bl.opt_mem_alignment =
+            MAX(bs->bl.opt_mem_alignment,
+                bs->backing_hd->bl.opt_mem_alignment);
+    }
+
+    /* Then let the driver override it */
+    if (drv->bdrv_refresh_limits) {
+        drv->bdrv_refresh_limits(bs, errp);
+    }
+}
+
+/**
+ * The copy-on-read flag is actually a reference count so multiple users may
+ * use the feature without worrying about clobbering its previous state.
+ * Copy-on-read stays enabled until all users have called to disable it.
+ */
+void bdrv_enable_copy_on_read(BlockDriverState *bs)
+{
+    bs->copy_on_read++;
+}
+
+void bdrv_disable_copy_on_read(BlockDriverState *bs)
+{
+    assert(bs->copy_on_read > 0);
+    bs->copy_on_read--;
+}
+
+/* Check if any requests are in-flight (including throttled requests) */
+static bool bdrv_requests_pending(BlockDriverState *bs)
+{
+    if (!QLIST_EMPTY(&bs->tracked_requests)) {
+        return true;
+    }
+    if (!qemu_co_queue_empty(&bs->throttled_reqs[0])) {
+        return true;
+    }
+    if (!qemu_co_queue_empty(&bs->throttled_reqs[1])) {
+        return true;
+    }
+    if (bs->file && bdrv_requests_pending(bs->file)) {
+        return true;
+    }
+    if (bs->backing_hd && bdrv_requests_pending(bs->backing_hd)) {
+        return true;
+    }
+    return false;
+}
+
+static bool bdrv_drain_one(BlockDriverState *bs)
+{
+    bool bs_busy;
+
+    bdrv_flush_io_queue(bs);
+    bdrv_start_throttled_reqs(bs);
+    bs_busy = bdrv_requests_pending(bs);
+    bs_busy |= aio_poll(bdrv_get_aio_context(bs), bs_busy);
+    return bs_busy;
+}
+
+/*
+ * Wait for pending requests to complete on a single BlockDriverState subtree
+ *
+ * See the warning in bdrv_drain_all().  This function can only be called if
+ * you are sure nothing can generate I/O because you have op blockers
+ * installed.
+ *
+ * Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState
+ * AioContext.
+ */
+void bdrv_drain(BlockDriverState *bs)
+{
+    while (bdrv_drain_one(bs)) {
+        /* Keep iterating */
+    }
+}
+
+/*
+ * Wait for pending requests to complete across all BlockDriverStates
+ *
+ * This function does not flush data to disk, use bdrv_flush_all() for that
+ * after calling this function.
+ *
+ * Note that completion of an asynchronous I/O operation can trigger any
+ * number of other I/O operations on other devices---for example a coroutine
+ * can be arbitrarily complex and a constant flow of I/O can come until the
+ * coroutine is complete.  Because of this, it is not possible to have a
+ * function to drain a single device's I/O queue.
+ */
+void bdrv_drain_all(void)
+{
+    /* Always run first iteration so any pending completion BHs run */
+    bool busy = true;
+    BlockDriverState *bs = NULL;
+
+    while ((bs = bdrv_next(bs))) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
+        if (bs->job) {
+            block_job_pause(bs->job);
+        }
+        aio_context_release(aio_context);
+    }
+
+    while (busy) {
+        busy = false;
+        bs = NULL;
+
+        while ((bs = bdrv_next(bs))) {
+            AioContext *aio_context = bdrv_get_aio_context(bs);
+
+            aio_context_acquire(aio_context);
+            busy |= bdrv_drain_one(bs);
+            aio_context_release(aio_context);
+        }
+    }
+
+    bs = NULL;
+    while ((bs = bdrv_next(bs))) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
+        if (bs->job) {
+            block_job_resume(bs->job);
+        }
+        aio_context_release(aio_context);
+    }
+}
+
+/**
+ * Remove an active request from the tracked requests list
+ *
+ * This function should be called when a tracked request is completing.
+ */
+static void tracked_request_end(BdrvTrackedRequest *req)
+{
+    if (req->serialising) {
+        req->bs->serialising_in_flight--;
+    }
+
+    QLIST_REMOVE(req, list);
+    qemu_co_queue_restart_all(&req->wait_queue);
+}
+
+/**
+ * Add an active request to the tracked requests list
+ */
+static void tracked_request_begin(BdrvTrackedRequest *req,
+                                  BlockDriverState *bs,
+                                  int64_t offset,
+                                  unsigned int bytes, bool is_write)
+{
+    *req = (BdrvTrackedRequest){
+        .bs = bs,
+        .offset         = offset,
+        .bytes          = bytes,
+        .is_write       = is_write,
+        .co             = qemu_coroutine_self(),
+        .serialising    = false,
+        .overlap_offset = offset,
+        .overlap_bytes  = bytes,
+    };
+
+    qemu_co_queue_init(&req->wait_queue);
+
+    QLIST_INSERT_HEAD(&bs->tracked_requests, req, list);
+}
+
+static void mark_request_serialising(BdrvTrackedRequest *req, uint64_t align)
+{
+    int64_t overlap_offset = req->offset & ~(align - 1);
+    unsigned int overlap_bytes = ROUND_UP(req->offset + req->bytes, align)
+                               - overlap_offset;
+
+    if (!req->serialising) {
+        req->bs->serialising_in_flight++;
+        req->serialising = true;
+    }
+
+    req->overlap_offset = MIN(req->overlap_offset, overlap_offset);
+    req->overlap_bytes = MAX(req->overlap_bytes, overlap_bytes);
+}
+
+/**
+ * Round a region to cluster boundaries
+ */
+void bdrv_round_to_clusters(BlockDriverState *bs,
+                            int64_t sector_num, int nb_sectors,
+                            int64_t *cluster_sector_num,
+                            int *cluster_nb_sectors)
+{
+    BlockDriverInfo bdi;
+
+    if (bdrv_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) {
+        *cluster_sector_num = sector_num;
+        *cluster_nb_sectors = nb_sectors;
+    } else {
+        int64_t c = bdi.cluster_size / BDRV_SECTOR_SIZE;
+        *cluster_sector_num = QEMU_ALIGN_DOWN(sector_num, c);
+        *cluster_nb_sectors = QEMU_ALIGN_UP(sector_num - *cluster_sector_num +
+                                            nb_sectors, c);
+    }
+}
+
+static int bdrv_get_cluster_size(BlockDriverState *bs)
+{
+    BlockDriverInfo bdi;
+    int ret;
+
+    ret = bdrv_get_info(bs, &bdi);
+    if (ret < 0 || bdi.cluster_size == 0) {
+        return bs->request_alignment;
+    } else {
+        return bdi.cluster_size;
+    }
+}
+
+static bool tracked_request_overlaps(BdrvTrackedRequest *req,
+                                     int64_t offset, unsigned int bytes)
+{
+    /*        aaaa   bbbb */
+    if (offset >= req->overlap_offset + req->overlap_bytes) {
+        return false;
+    }
+    /* bbbb   aaaa        */
+    if (req->overlap_offset >= offset + bytes) {
+        return false;
+    }
+    return true;
+}
+
+static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
+{
+    BlockDriverState *bs = self->bs;
+    BdrvTrackedRequest *req;
+    bool retry;
+    bool waited = false;
+
+    if (!bs->serialising_in_flight) {
+        return false;
+    }
+
+    do {
+        retry = false;
+        QLIST_FOREACH(req, &bs->tracked_requests, list) {
+            if (req == self || (!req->serialising && !self->serialising)) {
+                continue;
+            }
+            if (tracked_request_overlaps(req, self->overlap_offset,
+                                         self->overlap_bytes))
+            {
+                /* Hitting this means there was a reentrant request, for
+                 * example, a block driver issuing nested requests.  This must
+                 * never happen since it means deadlock.
+                 */
+                assert(qemu_coroutine_self() != req->co);
+
+                /* If the request is already (indirectly) waiting for us, or
+                 * will wait for us as soon as it wakes up, then just go on
+                 * (instead of producing a deadlock in the former case). */
+                if (!req->waiting_for) {
+                    self->waiting_for = req;
+                    qemu_co_queue_wait(&req->wait_queue);
+                    self->waiting_for = NULL;
+                    retry = true;
+                    waited = true;
+                    break;
+                }
+            }
+        }
+    } while (retry);
+
+    return waited;
+}
+
+static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,
+                                   size_t size)
+{
+    if (size > BDRV_REQUEST_MAX_SECTORS << BDRV_SECTOR_BITS) {
+        return -EIO;
+    }
+
+    if (!bdrv_is_inserted(bs)) {
+        return -ENOMEDIUM;
+    }
+
+    if (offset < 0) {
+        return -EIO;
+    }
+
+    return 0;
+}
+
+static int bdrv_check_request(BlockDriverState *bs, int64_t sector_num,
+                              int nb_sectors)
+{
+    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
+        return -EIO;
+    }
+
+    return bdrv_check_byte_request(bs, sector_num * BDRV_SECTOR_SIZE,
+                                   nb_sectors * BDRV_SECTOR_SIZE);
+}
+
+typedef struct RwCo {
+    BlockDriverState *bs;
+    int64_t offset;
+    QEMUIOVector *qiov;
+    bool is_write;
+    int ret;
+    BdrvRequestFlags flags;
+} RwCo;
+
+static void coroutine_fn bdrv_rw_co_entry(void *opaque)
+{
+    RwCo *rwco = opaque;
+
+    if (!rwco->is_write) {
+        rwco->ret = bdrv_co_do_preadv(rwco->bs, rwco->offset,
+                                      rwco->qiov->size, rwco->qiov,
+                                      rwco->flags);
+    } else {
+        rwco->ret = bdrv_co_do_pwritev(rwco->bs, rwco->offset,
+                                       rwco->qiov->size, rwco->qiov,
+                                       rwco->flags);
+    }
+}
+
+/*
+ * Process a vectored synchronous request using coroutines
+ */
+static int bdrv_prwv_co(BlockDriverState *bs, int64_t offset,
+                        QEMUIOVector *qiov, bool is_write,
+                        BdrvRequestFlags flags)
+{
+    Coroutine *co;
+    RwCo rwco = {
+        .bs = bs,
+        .offset = offset,
+        .qiov = qiov,
+        .is_write = is_write,
+        .ret = NOT_DONE,
+        .flags = flags,
+    };
+
+    /**
+     * In sync call context, when the vcpu is blocked, this throttling timer
+     * will not fire; so the I/O throttling function has to be disabled here
+     * if it has been enabled.
+     */
+    if (bs->io_limits_enabled) {
+        fprintf(stderr, "Disabling I/O throttling on '%s' due "
+                        "to synchronous I/O.\n", bdrv_get_device_name(bs));
+        bdrv_io_limits_disable(bs);
+    }
+
+    if (qemu_in_coroutine()) {
+        /* Fast-path if already in coroutine context */
+        bdrv_rw_co_entry(&rwco);
+    } else {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        co = qemu_coroutine_create(bdrv_rw_co_entry);
+        qemu_coroutine_enter(co, &rwco);
+        while (rwco.ret == NOT_DONE) {
+            aio_poll(aio_context, true);
+        }
+    }
+    return rwco.ret;
+}
+
+/*
+ * Process a synchronous request using coroutines
+ */
+static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
+                      int nb_sectors, bool is_write, BdrvRequestFlags flags)
+{
+    QEMUIOVector qiov;
+    struct iovec iov = {
+        .iov_base = (void *)buf,
+        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
+    };
+
+    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
+        return -EINVAL;
+    }
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    return bdrv_prwv_co(bs, sector_num << BDRV_SECTOR_BITS,
+                        &qiov, is_write, flags);
+}
+
+/* return < 0 if error. See bdrv_write() for the return codes */
+int bdrv_read(BlockDriverState *bs, int64_t sector_num,
+              uint8_t *buf, int nb_sectors)
+{
+    return bdrv_rw_co(bs, sector_num, buf, nb_sectors, false, 0);
+}
+
+/* Just like bdrv_read(), but with I/O throttling temporarily disabled */
+int bdrv_read_unthrottled(BlockDriverState *bs, int64_t sector_num,
+                          uint8_t *buf, int nb_sectors)
+{
+    bool enabled;
+    int ret;
+
+    enabled = bs->io_limits_enabled;
+    bs->io_limits_enabled = false;
+    ret = bdrv_read(bs, sector_num, buf, nb_sectors);
+    bs->io_limits_enabled = enabled;
+    return ret;
+}
+
+/* Return < 0 if error. Important errors are:
+  -EIO         generic I/O error (may happen for all errors)
+  -ENOMEDIUM   No media inserted.
+  -EINVAL      Invalid sector number or nb_sectors
+  -EACCES      Trying to write a read-only device
+*/
+int bdrv_write(BlockDriverState *bs, int64_t sector_num,
+               const uint8_t *buf, int nb_sectors)
+{
+    return bdrv_rw_co(bs, sector_num, (uint8_t *)buf, nb_sectors, true, 0);
+}
+
+int bdrv_write_zeroes(BlockDriverState *bs, int64_t sector_num,
+                      int nb_sectors, BdrvRequestFlags flags)
+{
+    return bdrv_rw_co(bs, sector_num, NULL, nb_sectors, true,
+                      BDRV_REQ_ZERO_WRITE | flags);
+}
+
+/*
+ * Completely zero out a block device with the help of bdrv_write_zeroes.
+ * The operation is sped up by checking the block status and only writing
+ * zeroes to the device if they currently do not return zeroes. Optional
+ * flags are passed through to bdrv_write_zeroes (e.g. BDRV_REQ_MAY_UNMAP).
+ *
+ * Returns < 0 on error, 0 on success. For error codes see bdrv_write().
+ */
+int bdrv_make_zero(BlockDriverState *bs, BdrvRequestFlags flags)
+{
+    int64_t target_sectors, ret, nb_sectors, sector_num = 0;
+    int n;
+
+    target_sectors = bdrv_nb_sectors(bs);
+    if (target_sectors < 0) {
+        return target_sectors;
+    }
+
+    for (;;) {
+        nb_sectors = MIN(target_sectors - sector_num, BDRV_REQUEST_MAX_SECTORS);
+        if (nb_sectors <= 0) {
+            return 0;
+        }
+        ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n);
+        if (ret < 0) {
+            error_report("error getting block status at sector %" PRId64 ": %s",
+                         sector_num, strerror(-ret));
+            return ret;
+        }
+        if (ret & BDRV_BLOCK_ZERO) {
+            sector_num += n;
+            continue;
+        }
+        ret = bdrv_write_zeroes(bs, sector_num, n, flags);
+        if (ret < 0) {
+            error_report("error writing zeroes at sector %" PRId64 ": %s",
+                         sector_num, strerror(-ret));
+            return ret;
+        }
+        sector_num += n;
+    }
+}
+
+int bdrv_pread(BlockDriverState *bs, int64_t offset, void *buf, int bytes)
+{
+    QEMUIOVector qiov;
+    struct iovec iov = {
+        .iov_base = (void *)buf,
+        .iov_len = bytes,
+    };
+    int ret;
+
+    if (bytes < 0) {
+        return -EINVAL;
+    }
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    ret = bdrv_prwv_co(bs, offset, &qiov, false, 0);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return bytes;
+}
+
+int bdrv_pwritev(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
+{
+    int ret;
+
+    ret = bdrv_prwv_co(bs, offset, qiov, true, 0);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return qiov->size;
+}
+
+int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
+                const void *buf, int bytes)
+{
+    QEMUIOVector qiov;
+    struct iovec iov = {
+        .iov_base   = (void *) buf,
+        .iov_len    = bytes,
+    };
+
+    if (bytes < 0) {
+        return -EINVAL;
+    }
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    return bdrv_pwritev(bs, offset, &qiov);
+}
+
+/*
+ * Writes to the file and ensures that no writes are reordered across this
+ * request (acts as a barrier)
+ *
+ * Returns 0 on success, -errno in error cases.
+ */
+int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset,
+    const void *buf, int count)
+{
+    int ret;
+
+    ret = bdrv_pwrite(bs, offset, buf, count);
+    if (ret < 0) {
+        return ret;
+    }
+
+    /* No flush needed for cache modes that already do it */
+    if (bs->enable_write_cache) {
+        bdrv_flush(bs);
+    }
+
+    return 0;
+}
+
+static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs,
+        int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
+{
+    /* Perform I/O through a temporary buffer so that users who scribble over
+     * their read buffer while the operation is in progress do not end up
+     * modifying the image file.  This is critical for zero-copy guest I/O
+     * where anything might happen inside guest memory.
+     */
+    void *bounce_buffer;
+
+    BlockDriver *drv = bs->drv;
+    struct iovec iov;
+    QEMUIOVector bounce_qiov;
+    int64_t cluster_sector_num;
+    int cluster_nb_sectors;
+    size_t skip_bytes;
+    int ret;
+
+    /* Cover entire cluster so no additional backing file I/O is required when
+     * allocating cluster in the image file.
+     */
+    bdrv_round_to_clusters(bs, sector_num, nb_sectors,
+                           &cluster_sector_num, &cluster_nb_sectors);
+
+    trace_bdrv_co_do_copy_on_readv(bs, sector_num, nb_sectors,
+                                   cluster_sector_num, cluster_nb_sectors);
+
+    iov.iov_len = cluster_nb_sectors * BDRV_SECTOR_SIZE;
+    iov.iov_base = bounce_buffer = qemu_try_blockalign(bs, iov.iov_len);
+    if (bounce_buffer == NULL) {
+        ret = -ENOMEM;
+        goto err;
+    }
+
+    qemu_iovec_init_external(&bounce_qiov, &iov, 1);
+
+    ret = drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors,
+                             &bounce_qiov);
+    if (ret < 0) {
+        goto err;
+    }
+
+    if (drv->bdrv_co_write_zeroes &&
+        buffer_is_zero(bounce_buffer, iov.iov_len)) {
+        ret = bdrv_co_do_write_zeroes(bs, cluster_sector_num,
+                                      cluster_nb_sectors, 0);
+    } else {
+        /* This does not change the data on the disk, it is not necessary
+         * to flush even in cache=writethrough mode.
+         */
+        ret = drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors,
+                                  &bounce_qiov);
+    }
+
+    if (ret < 0) {
+        /* It might be okay to ignore write errors for guest requests.  If this
+         * is a deliberate copy-on-read then we don't want to ignore the error.
+         * Simply report it in all cases.
+         */
+        goto err;
+    }
+
+    skip_bytes = (sector_num - cluster_sector_num) * BDRV_SECTOR_SIZE;
+    qemu_iovec_from_buf(qiov, 0, bounce_buffer + skip_bytes,
+                        nb_sectors * BDRV_SECTOR_SIZE);
+
+err:
+    qemu_vfree(bounce_buffer);
+    return ret;
+}
+
+/*
+ * Forwards an already correctly aligned request to the BlockDriver. This
+ * handles copy on read and zeroing after EOF; any other features must be
+ * implemented by the caller.
+ */
+static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
+    BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
+    int64_t align, QEMUIOVector *qiov, int flags)
+{
+    BlockDriver *drv = bs->drv;
+    int ret;
+
+    int64_t sector_num = offset >> BDRV_SECTOR_BITS;
+    unsigned int nb_sectors = bytes >> BDRV_SECTOR_BITS;
+
+    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
+    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
+    assert(!qiov || bytes == qiov->size);
+
+    /* Handle Copy on Read and associated serialisation */
+    if (flags & BDRV_REQ_COPY_ON_READ) {
+        /* If we touch the same cluster it counts as an overlap.  This
+         * guarantees that allocating writes will be serialized and not race
+         * with each other for the same cluster.  For example, in copy-on-read
+         * it ensures that the CoR read and write operations are atomic and
+         * guest writes cannot interleave between them. */
+        mark_request_serialising(req, bdrv_get_cluster_size(bs));
+    }
+
+    wait_serialising_requests(req);
+
+    if (flags & BDRV_REQ_COPY_ON_READ) {
+        int pnum;
+
+        ret = bdrv_is_allocated(bs, sector_num, nb_sectors, &pnum);
+        if (ret < 0) {
+            goto out;
+        }
+
+        if (!ret || pnum != nb_sectors) {
+            ret = bdrv_co_do_copy_on_readv(bs, sector_num, nb_sectors, qiov);
+            goto out;
+        }
+    }
+
+    /* Forward the request to the BlockDriver */
+    if (!bs->zero_beyond_eof) {
+        ret = drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
+    } else {
+        /* Read zeros after EOF */
+        int64_t total_sectors, max_nb_sectors;
+
+        total_sectors = bdrv_nb_sectors(bs);
+        if (total_sectors < 0) {
+            ret = total_sectors;
+            goto out;
+        }
+
+        max_nb_sectors = ROUND_UP(MAX(0, total_sectors - sector_num),
+                                  align >> BDRV_SECTOR_BITS);
+        if (nb_sectors < max_nb_sectors) {
+            ret = drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
+        } else if (max_nb_sectors > 0) {
+            QEMUIOVector local_qiov;
+
+            qemu_iovec_init(&local_qiov, qiov->niov);
+            qemu_iovec_concat(&local_qiov, qiov, 0,
+                              max_nb_sectors * BDRV_SECTOR_SIZE);
+
+            ret = drv->bdrv_co_readv(bs, sector_num, max_nb_sectors,
+                                     &local_qiov);
+
+            qemu_iovec_destroy(&local_qiov);
+        } else {
+            ret = 0;
+        }
+
+        /* Reading beyond end of file is supposed to produce zeroes */
+        if (ret == 0 && total_sectors < sector_num + nb_sectors) {
+            uint64_t offset = MAX(0, total_sectors - sector_num);
+            uint64_t bytes = (sector_num + nb_sectors - offset) *
+                              BDRV_SECTOR_SIZE;
+            qemu_iovec_memset(qiov, offset * BDRV_SECTOR_SIZE, 0, bytes);
+        }
+    }
+
+out:
+    return ret;
+}
+
+static inline uint64_t bdrv_get_align(BlockDriverState *bs)
+{
+    /* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
+    return MAX(BDRV_SECTOR_SIZE, bs->request_alignment);
+}
+
+static inline bool bdrv_req_is_aligned(BlockDriverState *bs,
+                                       int64_t offset, size_t bytes)
+{
+    int64_t align = bdrv_get_align(bs);
+    return !(offset & (align - 1) || (bytes & (align - 1)));
+}
+
+/*
+ * Handle a read request in coroutine context
+ */
+static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
+    int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
+    BdrvRequestFlags flags)
+{
+    BlockDriver *drv = bs->drv;
+    BdrvTrackedRequest req;
+
+    uint64_t align = bdrv_get_align(bs);
+    uint8_t *head_buf = NULL;
+    uint8_t *tail_buf = NULL;
+    QEMUIOVector local_qiov;
+    bool use_local_qiov = false;
+    int ret;
+
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
+    ret = bdrv_check_byte_request(bs, offset, bytes);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (bs->copy_on_read) {
+        flags |= BDRV_REQ_COPY_ON_READ;
+    }
+
+    /* throttling disk I/O */
+    if (bs->io_limits_enabled) {
+        bdrv_io_limits_intercept(bs, bytes, false);
+    }
+
+    /* Align read if necessary by padding qiov */
+    if (offset & (align - 1)) {
+        head_buf = qemu_blockalign(bs, align);
+        qemu_iovec_init(&local_qiov, qiov->niov + 2);
+        qemu_iovec_add(&local_qiov, head_buf, offset & (align - 1));
+        qemu_iovec_concat(&local_qiov, qiov, 0, qiov->size);
+        use_local_qiov = true;
+
+        bytes += offset & (align - 1);
+        offset = offset & ~(align - 1);
+    }
+
+    if ((offset + bytes) & (align - 1)) {
+        if (!use_local_qiov) {
+            qemu_iovec_init(&local_qiov, qiov->niov + 1);
+            qemu_iovec_concat(&local_qiov, qiov, 0, qiov->size);
+            use_local_qiov = true;
+        }
+        tail_buf = qemu_blockalign(bs, align);
+        qemu_iovec_add(&local_qiov, tail_buf,
+                       align - ((offset + bytes) & (align - 1)));
+
+        bytes = ROUND_UP(bytes, align);
+    }
+
+    tracked_request_begin(&req, bs, offset, bytes, false);
+    ret = bdrv_aligned_preadv(bs, &req, offset, bytes, align,
+                              use_local_qiov ? &local_qiov : qiov,
+                              flags);
+    tracked_request_end(&req);
+
+    if (use_local_qiov) {
+        qemu_iovec_destroy(&local_qiov);
+        qemu_vfree(head_buf);
+        qemu_vfree(tail_buf);
+    }
+
+    return ret;
+}
+
+static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
+    int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
+    BdrvRequestFlags flags)
+{
+    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
+        return -EINVAL;
+    }
+
+    return bdrv_co_do_preadv(bs, sector_num << BDRV_SECTOR_BITS,
+                             nb_sectors << BDRV_SECTOR_BITS, qiov, flags);
+}
+
+int coroutine_fn bdrv_co_readv(BlockDriverState *bs, int64_t sector_num,
+    int nb_sectors, QEMUIOVector *qiov)
+{
+    trace_bdrv_co_readv(bs, sector_num, nb_sectors);
+
+    return bdrv_co_do_readv(bs, sector_num, nb_sectors, qiov, 0);
+}
+
+int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
+    int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
+{
+    trace_bdrv_co_copy_on_readv(bs, sector_num, nb_sectors);
+
+    return bdrv_co_do_readv(bs, sector_num, nb_sectors, qiov,
+                            BDRV_REQ_COPY_ON_READ);
+}
+
+#define MAX_WRITE_ZEROES_BOUNCE_BUFFER 32768
+
+static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
+    int64_t sector_num, int nb_sectors, BdrvRequestFlags flags)
+{
+    BlockDriver *drv = bs->drv;
+    QEMUIOVector qiov;
+    struct iovec iov = {0};
+    int ret = 0;
+
+    int max_write_zeroes = MIN_NON_ZERO(bs->bl.max_write_zeroes,
+                                        BDRV_REQUEST_MAX_SECTORS);
+
+    while (nb_sectors > 0 && !ret) {
+        int num = nb_sectors;
+
+        /* Align request.  Block drivers can expect the "bulk" of the request
+         * to be aligned.
+         */
+        if (bs->bl.write_zeroes_alignment
+            && num > bs->bl.write_zeroes_alignment) {
+            if (sector_num % bs->bl.write_zeroes_alignment != 0) {
+                /* Make a small request up to the first aligned sector.  */
+                num = bs->bl.write_zeroes_alignment;
+                num -= sector_num % bs->bl.write_zeroes_alignment;
+            } else if ((sector_num + num) % bs->bl.write_zeroes_alignment != 0) {
+                /* Shorten the request to the last aligned sector.  num cannot
+                 * underflow because num > bs->bl.write_zeroes_alignment.
+                 */
+                num -= (sector_num + num) % bs->bl.write_zeroes_alignment;
+            }
+        }
+
+        /* limit request size */
+        if (num > max_write_zeroes) {
+            num = max_write_zeroes;
+        }
+
+        ret = -ENOTSUP;
+        /* First try the efficient write zeroes operation */
+        if (drv->bdrv_co_write_zeroes) {
+            ret = drv->bdrv_co_write_zeroes(bs, sector_num, num, flags);
+        }
+
+        if (ret == -ENOTSUP) {
+            /* Fall back to bounce buffer if write zeroes is unsupported */
+            int max_xfer_len = MIN_NON_ZERO(bs->bl.max_transfer_length,
+                                            MAX_WRITE_ZEROES_BOUNCE_BUFFER);
+            num = MIN(num, max_xfer_len);
+            iov.iov_len = num * BDRV_SECTOR_SIZE;
+            if (iov.iov_base == NULL) {
+                iov.iov_base = qemu_try_blockalign(bs, num * BDRV_SECTOR_SIZE);
+                if (iov.iov_base == NULL) {
+                    ret = -ENOMEM;
+                    goto fail;
+                }
+                memset(iov.iov_base, 0, num * BDRV_SECTOR_SIZE);
+            }
+            qemu_iovec_init_external(&qiov, &iov, 1);
+
+            ret = drv->bdrv_co_writev(bs, sector_num, num, &qiov);
+
+            /* Keep bounce buffer around if it is big enough for all
+             * all future requests.
+             */
+            if (num < max_xfer_len) {
+                qemu_vfree(iov.iov_base);
+                iov.iov_base = NULL;
+            }
+        }
+
+        sector_num += num;
+        nb_sectors -= num;
+    }
+
+fail:
+    qemu_vfree(iov.iov_base);
+    return ret;
+}
+
+/*
+ * Forwards an already correctly aligned write request to the BlockDriver.
+ */
+static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
+    BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
+    QEMUIOVector *qiov, int flags)
+{
+    BlockDriver *drv = bs->drv;
+    bool waited;
+    int ret;
+
+    int64_t sector_num = offset >> BDRV_SECTOR_BITS;
+    unsigned int nb_sectors = bytes >> BDRV_SECTOR_BITS;
+
+    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
+    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
+    assert(!qiov || bytes == qiov->size);
+
+    waited = wait_serialising_requests(req);
+    assert(!waited || !req->serialising);
+    assert(req->overlap_offset <= offset);
+    assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
+
+    ret = notifier_with_return_list_notify(&bs->before_write_notifiers, req);
+
+    if (!ret && bs->detect_zeroes != BLOCKDEV_DETECT_ZEROES_OPTIONS_OFF &&
+        !(flags & BDRV_REQ_ZERO_WRITE) && drv->bdrv_co_write_zeroes &&
+        qemu_iovec_is_zero(qiov)) {
+        flags |= BDRV_REQ_ZERO_WRITE;
+        if (bs->detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP) {
+            flags |= BDRV_REQ_MAY_UNMAP;
+        }
+    }
+
+    if (ret < 0) {
+        /* Do nothing, write notifier decided to fail this request */
+    } else if (flags & BDRV_REQ_ZERO_WRITE) {
+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_ZERO);
+        ret = bdrv_co_do_write_zeroes(bs, sector_num, nb_sectors, flags);
+    } else {
+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV);
+        ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, qiov);
+    }
+    BLKDBG_EVENT(bs, BLKDBG_PWRITEV_DONE);
+
+    if (ret == 0 && !bs->enable_write_cache) {
+        ret = bdrv_co_flush(bs);
+    }
+
+    bdrv_set_dirty(bs, sector_num, nb_sectors);
+
+    block_acct_highest_sector(&bs->stats, sector_num, nb_sectors);
+
+    if (ret >= 0) {
+        bs->total_sectors = MAX(bs->total_sectors, sector_num + nb_sectors);
+    }
+
+    return ret;
+}
+
+/*
+ * Handle a write request in coroutine context
+ */
+static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
+    int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
+    BdrvRequestFlags flags)
+{
+    BdrvTrackedRequest req;
+    uint64_t align = bdrv_get_align(bs);
+    uint8_t *head_buf = NULL;
+    uint8_t *tail_buf = NULL;
+    QEMUIOVector local_qiov;
+    bool use_local_qiov = false;
+    int ret;
+
+    if (!bs->drv) {
+        return -ENOMEDIUM;
+    }
+    if (bs->read_only) {
+        return -EACCES;
+    }
+
+    ret = bdrv_check_byte_request(bs, offset, bytes);
+    if (ret < 0) {
+        return ret;
+    }
+
+    /* throttling disk I/O */
+    if (bs->io_limits_enabled) {
+        bdrv_io_limits_intercept(bs, bytes, true);
+    }
+
+    /*
+     * Align write if necessary by performing a read-modify-write cycle.
+     * Pad qiov with the read parts and be sure to have a tracked request not
+     * only for bdrv_aligned_pwritev, but also for the reads of the RMW cycle.
+     */
+    tracked_request_begin(&req, bs, offset, bytes, true);
+
+    if (offset & (align - 1)) {
+        QEMUIOVector head_qiov;
+        struct iovec head_iov;
+
+        mark_request_serialising(&req, align);
+        wait_serialising_requests(&req);
+
+        head_buf = qemu_blockalign(bs, align);
+        head_iov = (struct iovec) {
+            .iov_base   = head_buf,
+            .iov_len    = align,
+        };
+        qemu_iovec_init_external(&head_qiov, &head_iov, 1);
+
+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_HEAD);
+        ret = bdrv_aligned_preadv(bs, &req, offset & ~(align - 1), align,
+                                  align, &head_qiov, 0);
+        if (ret < 0) {
+            goto fail;
+        }
+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_AFTER_HEAD);
+
+        qemu_iovec_init(&local_qiov, qiov->niov + 2);
+        qemu_iovec_add(&local_qiov, head_buf, offset & (align - 1));
+        qemu_iovec_concat(&local_qiov, qiov, 0, qiov->size);
+        use_local_qiov = true;
+
+        bytes += offset & (align - 1);
+        offset = offset & ~(align - 1);
+    }
+
+    if ((offset + bytes) & (align - 1)) {
+        QEMUIOVector tail_qiov;
+        struct iovec tail_iov;
+        size_t tail_bytes;
+        bool waited;
+
+        mark_request_serialising(&req, align);
+        waited = wait_serialising_requests(&req);
+        assert(!waited || !use_local_qiov);
+
+        tail_buf = qemu_blockalign(bs, align);
+        tail_iov = (struct iovec) {
+            .iov_base   = tail_buf,
+            .iov_len    = align,
+        };
+        qemu_iovec_init_external(&tail_qiov, &tail_iov, 1);
+
+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_TAIL);
+        ret = bdrv_aligned_preadv(bs, &req, (offset + bytes) & ~(align - 1), align,
+                                  align, &tail_qiov, 0);
+        if (ret < 0) {
+            goto fail;
+        }
+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_AFTER_TAIL);
+
+        if (!use_local_qiov) {
+            qemu_iovec_init(&local_qiov, qiov->niov + 1);
+            qemu_iovec_concat(&local_qiov, qiov, 0, qiov->size);
+            use_local_qiov = true;
+        }
+
+        tail_bytes = (offset + bytes) & (align - 1);
+        qemu_iovec_add(&local_qiov, tail_buf + tail_bytes, align - tail_bytes);
+
+        bytes = ROUND_UP(bytes, align);
+    }
+
+    if (use_local_qiov) {
+        /* Local buffer may have non-zero data. */
+        flags &= ~BDRV_REQ_ZERO_WRITE;
+    }
+    ret = bdrv_aligned_pwritev(bs, &req, offset, bytes,
+                               use_local_qiov ? &local_qiov : qiov,
+                               flags);
+
+fail:
+    tracked_request_end(&req);
+
+    if (use_local_qiov) {
+        qemu_iovec_destroy(&local_qiov);
+    }
+    qemu_vfree(head_buf);
+    qemu_vfree(tail_buf);
+
+    return ret;
+}
+
+static int coroutine_fn bdrv_co_do_writev(BlockDriverState *bs,
+    int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
+    BdrvRequestFlags flags)
+{
+    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
+        return -EINVAL;
+    }
+
+    return bdrv_co_do_pwritev(bs, sector_num << BDRV_SECTOR_BITS,
+                              nb_sectors << BDRV_SECTOR_BITS, qiov, flags);
+}
+
+int coroutine_fn bdrv_co_writev(BlockDriverState *bs, int64_t sector_num,
+    int nb_sectors, QEMUIOVector *qiov)
+{
+    trace_bdrv_co_writev(bs, sector_num, nb_sectors);
+
+    return bdrv_co_do_writev(bs, sector_num, nb_sectors, qiov, 0);
+}
+
+int coroutine_fn bdrv_co_write_zeroes(BlockDriverState *bs,
+                                      int64_t sector_num, int nb_sectors,
+                                      BdrvRequestFlags flags)
+{
+    int ret;
+
+    trace_bdrv_co_write_zeroes(bs, sector_num, nb_sectors, flags);
+
+    if (!(bs->open_flags & BDRV_O_UNMAP)) {
+        flags &= ~BDRV_REQ_MAY_UNMAP;
+    }
+    if (bdrv_req_is_aligned(bs, sector_num << BDRV_SECTOR_BITS,
+                            nb_sectors << BDRV_SECTOR_BITS)) {
+        ret = bdrv_co_do_writev(bs, sector_num, nb_sectors, NULL,
+                                BDRV_REQ_ZERO_WRITE | flags);
+    } else {
+        uint8_t *buf;
+        QEMUIOVector local_qiov;
+        size_t bytes = nb_sectors << BDRV_SECTOR_BITS;
+
+        buf = qemu_memalign(bdrv_opt_mem_align(bs), bytes);
+        memset(buf, 0, bytes);
+        qemu_iovec_init(&local_qiov, 1);
+        qemu_iovec_add(&local_qiov, buf, bytes);
+
+        ret = bdrv_co_do_writev(bs, sector_num, nb_sectors, &local_qiov,
+                                BDRV_REQ_ZERO_WRITE | flags);
+        qemu_vfree(buf);
+    }
+    return ret;
+}
+
+int bdrv_flush_all(void)
+{
+    BlockDriverState *bs = NULL;
+    int result = 0;
+
+    while ((bs = bdrv_next(bs))) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+        int ret;
+
+        aio_context_acquire(aio_context);
+        ret = bdrv_flush(bs);
+        if (ret < 0 && !result) {
+            result = ret;
+        }
+        aio_context_release(aio_context);
+    }
+
+    return result;
+}
+
+typedef struct BdrvCoGetBlockStatusData {
+    BlockDriverState *bs;
+    BlockDriverState *base;
+    int64_t sector_num;
+    int nb_sectors;
+    int *pnum;
+    int64_t ret;
+    bool done;
+} BdrvCoGetBlockStatusData;
+
+/*
+ * Returns the allocation status of the specified sectors.
+ * Drivers not implementing the functionality are assumed to not support
+ * backing files, hence all their sectors are reported as allocated.
+ *
+ * If 'sector_num' is beyond the end of the disk image the return value is 0
+ * and 'pnum' is set to 0.
+ *
+ * 'pnum' is set to the number of sectors (including and immediately following
+ * the specified sector) that are known to be in the same
+ * allocated/unallocated state.
+ *
+ * 'nb_sectors' is the max value 'pnum' should be set to.  If nb_sectors goes
+ * beyond the end of the disk image it will be clamped.
+ */
+static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
+                                                     int64_t sector_num,
+                                                     int nb_sectors, int *pnum)
+{
+    int64_t total_sectors;
+    int64_t n;
+    int64_t ret, ret2;
+
+    total_sectors = bdrv_nb_sectors(bs);
+    if (total_sectors < 0) {
+        return total_sectors;
+    }
+
+    if (sector_num >= total_sectors) {
+        *pnum = 0;
+        return 0;
+    }
+
+    n = total_sectors - sector_num;
+    if (n < nb_sectors) {
+        nb_sectors = n;
+    }
+
+    if (!bs->drv->bdrv_co_get_block_status) {
+        *pnum = nb_sectors;
+        ret = BDRV_BLOCK_DATA | BDRV_BLOCK_ALLOCATED;
+        if (bs->drv->protocol_name) {
+            ret |= BDRV_BLOCK_OFFSET_VALID | (sector_num * BDRV_SECTOR_SIZE);
+        }
+        return ret;
+    }
+
+    ret = bs->drv->bdrv_co_get_block_status(bs, sector_num, nb_sectors, pnum);
+    if (ret < 0) {
+        *pnum = 0;
+        return ret;
+    }
+
+    if (ret & BDRV_BLOCK_RAW) {
+        assert(ret & BDRV_BLOCK_OFFSET_VALID);
+        return bdrv_get_block_status(bs->file, ret >> BDRV_SECTOR_BITS,
+                                     *pnum, pnum);
+    }
+
+    if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) {
+        ret |= BDRV_BLOCK_ALLOCATED;
+    }
+
+    if (!(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO)) {
+        if (bdrv_unallocated_blocks_are_zero(bs)) {
+            ret |= BDRV_BLOCK_ZERO;
+        } else if (bs->backing_hd) {
+            BlockDriverState *bs2 = bs->backing_hd;
+            int64_t nb_sectors2 = bdrv_nb_sectors(bs2);
+            if (nb_sectors2 >= 0 && sector_num >= nb_sectors2) {
+                ret |= BDRV_BLOCK_ZERO;
+            }
+        }
+    }
+
+    if (bs->file &&
+        (ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO) &&
+        (ret & BDRV_BLOCK_OFFSET_VALID)) {
+        int file_pnum;
+
+        ret2 = bdrv_co_get_block_status(bs->file, ret >> BDRV_SECTOR_BITS,
+                                        *pnum, &file_pnum);
+        if (ret2 >= 0) {
+            /* Ignore errors.  This is just providing extra information, it
+             * is useful but not necessary.
+             */
+            if (!file_pnum) {
+                /* !file_pnum indicates an offset at or beyond the EOF; it is
+                 * perfectly valid for the format block driver to point to such
+                 * offsets, so catch it and mark everything as zero */
+                ret |= BDRV_BLOCK_ZERO;
+            } else {
+                /* Limit request to the range reported by the protocol driver */
+                *pnum = file_pnum;
+                ret |= (ret2 & BDRV_BLOCK_ZERO);
+            }
+        }
+    }
+
+    return ret;
+}
+
+/* Coroutine wrapper for bdrv_get_block_status() */
+static void coroutine_fn bdrv_get_block_status_co_entry(void *opaque)
+{
+    BdrvCoGetBlockStatusData *data = opaque;
+    BlockDriverState *bs = data->bs;
+
+    data->ret = bdrv_co_get_block_status(bs, data->sector_num, data->nb_sectors,
+                                         data->pnum);
+    data->done = true;
+}
+
+/*
+ * Synchronous wrapper around bdrv_co_get_block_status().
+ *
+ * See bdrv_co_get_block_status() for details.
+ */
+int64_t bdrv_get_block_status(BlockDriverState *bs, int64_t sector_num,
+                              int nb_sectors, int *pnum)
+{
+    Coroutine *co;
+    BdrvCoGetBlockStatusData data = {
+        .bs = bs,
+        .sector_num = sector_num,
+        .nb_sectors = nb_sectors,
+        .pnum = pnum,
+        .done = false,
+    };
+
+    if (qemu_in_coroutine()) {
+        /* Fast-path if already in coroutine context */
+        bdrv_get_block_status_co_entry(&data);
+    } else {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        co = qemu_coroutine_create(bdrv_get_block_status_co_entry);
+        qemu_coroutine_enter(co, &data);
+        while (!data.done) {
+            aio_poll(aio_context, true);
+        }
+    }
+    return data.ret;
+}
+
+int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num,
+                                   int nb_sectors, int *pnum)
+{
+    int64_t ret = bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
+    if (ret < 0) {
+        return ret;
+    }
+    return !!(ret & BDRV_BLOCK_ALLOCATED);
+}
+
+/*
+ * Given an image chain: ... -> [BASE] -> [INTER1] -> [INTER2] -> [TOP]
+ *
+ * Return true if the given sector is allocated in any image between
+ * BASE and TOP (inclusive).  BASE can be NULL to check if the given
+ * sector is allocated in any image of the chain.  Return false otherwise.
+ *
+ * 'pnum' is set to the number of sectors (including and immediately following
+ *  the specified sector) that are known to be in the same
+ *  allocated/unallocated state.
+ *
+ */
+int bdrv_is_allocated_above(BlockDriverState *top,
+                            BlockDriverState *base,
+                            int64_t sector_num,
+                            int nb_sectors, int *pnum)
+{
+    BlockDriverState *intermediate;
+    int ret, n = nb_sectors;
+
+    intermediate = top;
+    while (intermediate && intermediate != base) {
+        int pnum_inter;
+        ret = bdrv_is_allocated(intermediate, sector_num, nb_sectors,
+                                &pnum_inter);
+        if (ret < 0) {
+            return ret;
+        } else if (ret) {
+            *pnum = pnum_inter;
+            return 1;
+        }
+
+        /*
+         * [sector_num, nb_sectors] is unallocated on top but intermediate
+         * might have
+         *
+         * [sector_num+x, nr_sectors] allocated.
+         */
+        if (n > pnum_inter &&
+            (intermediate == top ||
+             sector_num + pnum_inter < intermediate->total_sectors)) {
+            n = pnum_inter;
+        }
+
+        intermediate = intermediate->backing_hd;
+    }
+
+    *pnum = n;
+    return 0;
+}
+
+int bdrv_write_compressed(BlockDriverState *bs, int64_t sector_num,
+                          const uint8_t *buf, int nb_sectors)
+{
+    BlockDriver *drv = bs->drv;
+    int ret;
+
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+    if (!drv->bdrv_write_compressed) {
+        return -ENOTSUP;
+    }
+    ret = bdrv_check_request(bs, sector_num, nb_sectors);
+    if (ret < 0) {
+        return ret;
+    }
+
+    assert(QLIST_EMPTY(&bs->dirty_bitmaps));
+
+    return drv->bdrv_write_compressed(bs, sector_num, buf, nb_sectors);
+}
+
+int bdrv_save_vmstate(BlockDriverState *bs, const uint8_t *buf,
+                      int64_t pos, int size)
+{
+    QEMUIOVector qiov;
+    struct iovec iov = {
+        .iov_base   = (void *) buf,
+        .iov_len    = size,
+    };
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    return bdrv_writev_vmstate(bs, &qiov, pos);
+}
+
+int bdrv_writev_vmstate(BlockDriverState *bs, QEMUIOVector *qiov, int64_t pos)
+{
+    BlockDriver *drv = bs->drv;
+
+    if (!drv) {
+        return -ENOMEDIUM;
+    } else if (drv->bdrv_save_vmstate) {
+        return drv->bdrv_save_vmstate(bs, qiov, pos);
+    } else if (bs->file) {
+        return bdrv_writev_vmstate(bs->file, qiov, pos);
+    }
+
+    return -ENOTSUP;
+}
+
+int bdrv_load_vmstate(BlockDriverState *bs, uint8_t *buf,
+                      int64_t pos, int size)
+{
+    BlockDriver *drv = bs->drv;
+    if (!drv)
+        return -ENOMEDIUM;
+    if (drv->bdrv_load_vmstate)
+        return drv->bdrv_load_vmstate(bs, buf, pos, size);
+    if (bs->file)
+        return bdrv_load_vmstate(bs->file, buf, pos, size);
+    return -ENOTSUP;
+}
+
+/**************************************************************/
+/* async I/Os */
+
+BlockAIOCB *bdrv_aio_readv(BlockDriverState *bs, int64_t sector_num,
+                           QEMUIOVector *qiov, int nb_sectors,
+                           BlockCompletionFunc *cb, void *opaque)
+{
+    trace_bdrv_aio_readv(bs, sector_num, nb_sectors, opaque);
+
+    return bdrv_co_aio_rw_vector(bs, sector_num, qiov, nb_sectors, 0,
+                                 cb, opaque, false);
+}
+
+BlockAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
+                            QEMUIOVector *qiov, int nb_sectors,
+                            BlockCompletionFunc *cb, void *opaque)
+{
+    trace_bdrv_aio_writev(bs, sector_num, nb_sectors, opaque);
+
+    return bdrv_co_aio_rw_vector(bs, sector_num, qiov, nb_sectors, 0,
+                                 cb, opaque, true);
+}
+
+BlockAIOCB *bdrv_aio_write_zeroes(BlockDriverState *bs,
+        int64_t sector_num, int nb_sectors, BdrvRequestFlags flags,
+        BlockCompletionFunc *cb, void *opaque)
+{
+    trace_bdrv_aio_write_zeroes(bs, sector_num, nb_sectors, flags, opaque);
+
+    return bdrv_co_aio_rw_vector(bs, sector_num, NULL, nb_sectors,
+                                 BDRV_REQ_ZERO_WRITE | flags,
+                                 cb, opaque, true);
+}
+
+
+typedef struct MultiwriteCB {
+    int error;
+    int num_requests;
+    int num_callbacks;
+    struct {
+        BlockCompletionFunc *cb;
+        void *opaque;
+        QEMUIOVector *free_qiov;
+    } callbacks[];
+} MultiwriteCB;
+
+static void multiwrite_user_cb(MultiwriteCB *mcb)
+{
+    int i;
+
+    for (i = 0; i < mcb->num_callbacks; i++) {
+        mcb->callbacks[i].cb(mcb->callbacks[i].opaque, mcb->error);
+        if (mcb->callbacks[i].free_qiov) {
+            qemu_iovec_destroy(mcb->callbacks[i].free_qiov);
+        }
+        g_free(mcb->callbacks[i].free_qiov);
+    }
+}
+
+static void multiwrite_cb(void *opaque, int ret)
+{
+    MultiwriteCB *mcb = opaque;
+
+    trace_multiwrite_cb(mcb, ret);
+
+    if (ret < 0 && !mcb->error) {
+        mcb->error = ret;
+    }
+
+    mcb->num_requests--;
+    if (mcb->num_requests == 0) {
+        multiwrite_user_cb(mcb);
+        g_free(mcb);
+    }
+}
+
+static int multiwrite_req_compare(const void *a, const void *b)
+{
+    const BlockRequest *req1 = a, *req2 = b;
+
+    /*
+     * Note that we can't simply subtract req2->sector from req1->sector
+     * here as that could overflow the return value.
+     */
+    if (req1->sector > req2->sector) {
+        return 1;
+    } else if (req1->sector < req2->sector) {
+        return -1;
+    } else {
+        return 0;
+    }
+}
+
+/*
+ * Takes a bunch of requests and tries to merge them. Returns the number of
+ * requests that remain after merging.
+ */
+static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
+    int num_reqs, MultiwriteCB *mcb)
+{
+    int i, outidx;
+
+    // Sort requests by start sector
+    qsort(reqs, num_reqs, sizeof(*reqs), &multiwrite_req_compare);
+
+    // Check if adjacent requests touch the same clusters. If so, combine them,
+    // filling up gaps with zero sectors.
+    outidx = 0;
+    for (i = 1; i < num_reqs; i++) {
+        int merge = 0;
+        int64_t oldreq_last = reqs[outidx].sector + reqs[outidx].nb_sectors;
+
+        // Handle exactly sequential writes and overlapping writes.
+        if (reqs[i].sector <= oldreq_last) {
+            merge = 1;
+        }
+
+        if (reqs[outidx].qiov->niov + reqs[i].qiov->niov + 1 > IOV_MAX) {
+            merge = 0;
+        }
+
+        if (bs->bl.max_transfer_length && reqs[outidx].nb_sectors +
+            reqs[i].nb_sectors > bs->bl.max_transfer_length) {
+            merge = 0;
+        }
+
+        if (merge) {
+            size_t size;
+            QEMUIOVector *qiov = g_malloc0(sizeof(*qiov));
+            qemu_iovec_init(qiov,
+                reqs[outidx].qiov->niov + reqs[i].qiov->niov + 1);
+
+            // Add the first request to the merged one. If the requests are
+            // overlapping, drop the last sectors of the first request.
+            size = (reqs[i].sector - reqs[outidx].sector) << 9;
+            qemu_iovec_concat(qiov, reqs[outidx].qiov, 0, size);
+
+            // We should need to add any zeros between the two requests
+            assert (reqs[i].sector <= oldreq_last);
+
+            // Add the second request
+            qemu_iovec_concat(qiov, reqs[i].qiov, 0, reqs[i].qiov->size);
+
+            // Add tail of first request, if necessary
+            if (qiov->size < reqs[outidx].qiov->size) {
+                qemu_iovec_concat(qiov, reqs[outidx].qiov, qiov->size,
+                                  reqs[outidx].qiov->size - qiov->size);
+            }
+
+            reqs[outidx].nb_sectors = qiov->size >> 9;
+            reqs[outidx].qiov = qiov;
+
+            mcb->callbacks[i].free_qiov = reqs[outidx].qiov;
+        } else {
+            outidx++;
+            reqs[outidx].sector     = reqs[i].sector;
+            reqs[outidx].nb_sectors = reqs[i].nb_sectors;
+            reqs[outidx].qiov       = reqs[i].qiov;
+        }
+    }
+
+    block_acct_merge_done(&bs->stats, BLOCK_ACCT_WRITE, num_reqs - outidx - 1);
+
+    return outidx + 1;
+}
+
+/*
+ * Submit multiple AIO write requests at once.
+ *
+ * On success, the function returns 0 and all requests in the reqs array have
+ * been submitted. In error case this function returns -1, and any of the
+ * requests may or may not be submitted yet. In particular, this means that the
+ * callback will be called for some of the requests, for others it won't. The
+ * caller must check the error field of the BlockRequest to wait for the right
+ * callbacks (if error != 0, no callback will be called).
+ *
+ * The implementation may modify the contents of the reqs array, e.g. to merge
+ * requests. However, the fields opaque and error are left unmodified as they
+ * are used to signal failure for a single request to the caller.
+ */
+int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs)
+{
+    MultiwriteCB *mcb;
+    int i;
+
+    /* don't submit writes if we don't have a medium */
+    if (bs->drv == NULL) {
+        for (i = 0; i < num_reqs; i++) {
+            reqs[i].error = -ENOMEDIUM;
+        }
+        return -1;
+    }
+
+    if (num_reqs == 0) {
+        return 0;
+    }
+
+    // Create MultiwriteCB structure
+    mcb = g_malloc0(sizeof(*mcb) + num_reqs * sizeof(*mcb->callbacks));
+    mcb->num_requests = 0;
+    mcb->num_callbacks = num_reqs;
+
+    for (i = 0; i < num_reqs; i++) {
+        mcb->callbacks[i].cb = reqs[i].cb;
+        mcb->callbacks[i].opaque = reqs[i].opaque;
+    }
+
+    // Check for mergable requests
+    num_reqs = multiwrite_merge(bs, reqs, num_reqs, mcb);
+
+    trace_bdrv_aio_multiwrite(mcb, mcb->num_callbacks, num_reqs);
+
+    /* Run the aio requests. */
+    mcb->num_requests = num_reqs;
+    for (i = 0; i < num_reqs; i++) {
+        bdrv_co_aio_rw_vector(bs, reqs[i].sector, reqs[i].qiov,
+                              reqs[i].nb_sectors, reqs[i].flags,
+                              multiwrite_cb, mcb,
+                              true);
+    }
+
+    return 0;
+}
+
+void bdrv_aio_cancel(BlockAIOCB *acb)
+{
+    qemu_aio_ref(acb);
+    bdrv_aio_cancel_async(acb);
+    while (acb->refcnt > 1) {
+        if (acb->aiocb_info->get_aio_context) {
+            aio_poll(acb->aiocb_info->get_aio_context(acb), true);
+        } else if (acb->bs) {
+            aio_poll(bdrv_get_aio_context(acb->bs), true);
+        } else {
+            abort();
+        }
+    }
+    qemu_aio_unref(acb);
+}
+
+/* Async version of aio cancel. The caller is not blocked if the acb implements
+ * cancel_async, otherwise we do nothing and let the request normally complete.
+ * In either case the completion callback must be called. */
+void bdrv_aio_cancel_async(BlockAIOCB *acb)
+{
+    if (acb->aiocb_info->cancel_async) {
+        acb->aiocb_info->cancel_async(acb);
+    }
+}
+
+/**************************************************************/
+/* async block device emulation */
+
+typedef struct BlockAIOCBSync {
+    BlockAIOCB common;
+    QEMUBH *bh;
+    int ret;
+    /* vector translation state */
+    QEMUIOVector *qiov;
+    uint8_t *bounce;
+    int is_write;
+} BlockAIOCBSync;
+
+static const AIOCBInfo bdrv_em_aiocb_info = {
+    .aiocb_size         = sizeof(BlockAIOCBSync),
+};
+
+static void bdrv_aio_bh_cb(void *opaque)
+{
+    BlockAIOCBSync *acb = opaque;
+
+    if (!acb->is_write && acb->ret >= 0) {
+        qemu_iovec_from_buf(acb->qiov, 0, acb->bounce, acb->qiov->size);
+    }
+    qemu_vfree(acb->bounce);
+    acb->common.cb(acb->common.opaque, acb->ret);
+    qemu_bh_delete(acb->bh);
+    acb->bh = NULL;
+    qemu_aio_unref(acb);
+}
+
+static BlockAIOCB *bdrv_aio_rw_vector(BlockDriverState *bs,
+                                      int64_t sector_num,
+                                      QEMUIOVector *qiov,
+                                      int nb_sectors,
+                                      BlockCompletionFunc *cb,
+                                      void *opaque,
+                                      int is_write)
+
+{
+    BlockAIOCBSync *acb;
+
+    acb = qemu_aio_get(&bdrv_em_aiocb_info, bs, cb, opaque);
+    acb->is_write = is_write;
+    acb->qiov = qiov;
+    acb->bounce = qemu_try_blockalign(bs, qiov->size);
+    acb->bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_aio_bh_cb, acb);
+
+    if (acb->bounce == NULL) {
+        acb->ret = -ENOMEM;
+    } else if (is_write) {
+        qemu_iovec_to_buf(acb->qiov, 0, acb->bounce, qiov->size);
+        acb->ret = bs->drv->bdrv_write(bs, sector_num, acb->bounce, nb_sectors);
+    } else {
+        acb->ret = bs->drv->bdrv_read(bs, sector_num, acb->bounce, nb_sectors);
+    }
+
+    qemu_bh_schedule(acb->bh);
+
+    return &acb->common;
+}
+
+static BlockAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,
+        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
+        BlockCompletionFunc *cb, void *opaque)
+{
+    return bdrv_aio_rw_vector(bs, sector_num, qiov, nb_sectors, cb, opaque, 0);
+}
+
+static BlockAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,
+        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
+        BlockCompletionFunc *cb, void *opaque)
+{
+    return bdrv_aio_rw_vector(bs, sector_num, qiov, nb_sectors, cb, opaque, 1);
+}
+
+
+typedef struct BlockAIOCBCoroutine {
+    BlockAIOCB common;
+    BlockRequest req;
+    bool is_write;
+    bool need_bh;
+    bool *done;
+    QEMUBH* bh;
+} BlockAIOCBCoroutine;
+
+static const AIOCBInfo bdrv_em_co_aiocb_info = {
+    .aiocb_size         = sizeof(BlockAIOCBCoroutine),
+};
+
+static void bdrv_co_complete(BlockAIOCBCoroutine *acb)
+{
+    if (!acb->need_bh) {
+        acb->common.cb(acb->common.opaque, acb->req.error);
+        qemu_aio_unref(acb);
+    }
+}
+
+static void bdrv_co_em_bh(void *opaque)
+{
+    BlockAIOCBCoroutine *acb = opaque;
+
+    assert(!acb->need_bh);
+    qemu_bh_delete(acb->bh);
+    bdrv_co_complete(acb);
+}
+
+static void bdrv_co_maybe_schedule_bh(BlockAIOCBCoroutine *acb)
+{
+    acb->need_bh = false;
+    if (acb->req.error != -EINPROGRESS) {
+        BlockDriverState *bs = acb->common.bs;
+
+        acb->bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_co_em_bh, acb);
+        qemu_bh_schedule(acb->bh);
+    }
+}
+
+/* Invoke bdrv_co_do_readv/bdrv_co_do_writev */
+static void coroutine_fn bdrv_co_do_rw(void *opaque)
+{
+    BlockAIOCBCoroutine *acb = opaque;
+    BlockDriverState *bs = acb->common.bs;
+
+    if (!acb->is_write) {
+        acb->req.error = bdrv_co_do_readv(bs, acb->req.sector,
+            acb->req.nb_sectors, acb->req.qiov, acb->req.flags);
+    } else {
+        acb->req.error = bdrv_co_do_writev(bs, acb->req.sector,
+            acb->req.nb_sectors, acb->req.qiov, acb->req.flags);
+    }
+
+    bdrv_co_complete(acb);
+}
+
+static BlockAIOCB *bdrv_co_aio_rw_vector(BlockDriverState *bs,
+                                         int64_t sector_num,
+                                         QEMUIOVector *qiov,
+                                         int nb_sectors,
+                                         BdrvRequestFlags flags,
+                                         BlockCompletionFunc *cb,
+                                         void *opaque,
+                                         bool is_write)
+{
+    Coroutine *co;
+    BlockAIOCBCoroutine *acb;
+
+    acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
+    acb->need_bh = true;
+    acb->req.error = -EINPROGRESS;
+    acb->req.sector = sector_num;
+    acb->req.nb_sectors = nb_sectors;
+    acb->req.qiov = qiov;
+    acb->req.flags = flags;
+    acb->is_write = is_write;
+
+    co = qemu_coroutine_create(bdrv_co_do_rw);
+    qemu_coroutine_enter(co, acb);
+
+    bdrv_co_maybe_schedule_bh(acb);
+    return &acb->common;
+}
+
+static void coroutine_fn bdrv_aio_flush_co_entry(void *opaque)
+{
+    BlockAIOCBCoroutine *acb = opaque;
+    BlockDriverState *bs = acb->common.bs;
+
+    acb->req.error = bdrv_co_flush(bs);
+    bdrv_co_complete(acb);
+}
+
+BlockAIOCB *bdrv_aio_flush(BlockDriverState *bs,
+        BlockCompletionFunc *cb, void *opaque)
+{
+    trace_bdrv_aio_flush(bs, opaque);
+
+    Coroutine *co;
+    BlockAIOCBCoroutine *acb;
+
+    acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
+    acb->need_bh = true;
+    acb->req.error = -EINPROGRESS;
+
+    co = qemu_coroutine_create(bdrv_aio_flush_co_entry);
+    qemu_coroutine_enter(co, acb);
+
+    bdrv_co_maybe_schedule_bh(acb);
+    return &acb->common;
+}
+
+static void coroutine_fn bdrv_aio_discard_co_entry(void *opaque)
+{
+    BlockAIOCBCoroutine *acb = opaque;
+    BlockDriverState *bs = acb->common.bs;
+
+    acb->req.error = bdrv_co_discard(bs, acb->req.sector, acb->req.nb_sectors);
+    bdrv_co_complete(acb);
+}
+
+BlockAIOCB *bdrv_aio_discard(BlockDriverState *bs,
+        int64_t sector_num, int nb_sectors,
+        BlockCompletionFunc *cb, void *opaque)
+{
+    Coroutine *co;
+    BlockAIOCBCoroutine *acb;
+
+    trace_bdrv_aio_discard(bs, sector_num, nb_sectors, opaque);
+
+    acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
+    acb->need_bh = true;
+    acb->req.error = -EINPROGRESS;
+    acb->req.sector = sector_num;
+    acb->req.nb_sectors = nb_sectors;
+    co = qemu_coroutine_create(bdrv_aio_discard_co_entry);
+    qemu_coroutine_enter(co, acb);
+
+    bdrv_co_maybe_schedule_bh(acb);
+    return &acb->common;
+}
+
+void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs,
+                   BlockCompletionFunc *cb, void *opaque)
+{
+    BlockAIOCB *acb;
+
+    acb = g_slice_alloc(aiocb_info->aiocb_size);
+    acb->aiocb_info = aiocb_info;
+    acb->bs = bs;
+    acb->cb = cb;
+    acb->opaque = opaque;
+    acb->refcnt = 1;
+    return acb;
+}
+
+void qemu_aio_ref(void *p)
+{
+    BlockAIOCB *acb = p;
+    acb->refcnt++;
+}
+
+void qemu_aio_unref(void *p)
+{
+    BlockAIOCB *acb = p;
+    assert(acb->refcnt > 0);
+    if (--acb->refcnt == 0) {
+        g_slice_free1(acb->aiocb_info->aiocb_size, acb);
+    }
+}
+
+/**************************************************************/
+/* Coroutine block device emulation */
+
+typedef struct CoroutineIOCompletion {
+    Coroutine *coroutine;
+    int ret;
+} CoroutineIOCompletion;
+
+static void bdrv_co_io_em_complete(void *opaque, int ret)
+{
+    CoroutineIOCompletion *co = opaque;
+
+    co->ret = ret;
+    qemu_coroutine_enter(co->coroutine, NULL);
+}
+
+static int coroutine_fn bdrv_co_io_em(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *iov,
+                                      bool is_write)
+{
+    CoroutineIOCompletion co = {
+        .coroutine = qemu_coroutine_self(),
+    };
+    BlockAIOCB *acb;
+
+    if (is_write) {
+        acb = bs->drv->bdrv_aio_writev(bs, sector_num, iov, nb_sectors,
+                                       bdrv_co_io_em_complete, &co);
+    } else {
+        acb = bs->drv->bdrv_aio_readv(bs, sector_num, iov, nb_sectors,
+                                      bdrv_co_io_em_complete, &co);
+    }
+
+    trace_bdrv_co_io_em(bs, sector_num, nb_sectors, is_write, acb);
+    if (!acb) {
+        return -EIO;
+    }
+    qemu_coroutine_yield();
+
+    return co.ret;
+}
+
+static int coroutine_fn bdrv_co_readv_em(BlockDriverState *bs,
+                                         int64_t sector_num, int nb_sectors,
+                                         QEMUIOVector *iov)
+{
+    return bdrv_co_io_em(bs, sector_num, nb_sectors, iov, false);
+}
+
+static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
+                                         int64_t sector_num, int nb_sectors,
+                                         QEMUIOVector *iov)
+{
+    return bdrv_co_io_em(bs, sector_num, nb_sectors, iov, true);
+}
+
+static void coroutine_fn bdrv_flush_co_entry(void *opaque)
+{
+    RwCo *rwco = opaque;
+
+    rwco->ret = bdrv_co_flush(rwco->bs);
+}
+
+int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
+{
+    int ret;
+
+    if (!bs || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
+        return 0;
+    }
+
+    /* Write back cached data to the OS even with cache=unsafe */
+    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_OS);
+    if (bs->drv->bdrv_co_flush_to_os) {
+        ret = bs->drv->bdrv_co_flush_to_os(bs);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    /* But don't actually force it to the disk with cache=unsafe */
+    if (bs->open_flags & BDRV_O_NO_FLUSH) {
+        goto flush_parent;
+    }
+
+    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_DISK);
+    if (bs->drv->bdrv_co_flush_to_disk) {
+        ret = bs->drv->bdrv_co_flush_to_disk(bs);
+    } else if (bs->drv->bdrv_aio_flush) {
+        BlockAIOCB *acb;
+        CoroutineIOCompletion co = {
+            .coroutine = qemu_coroutine_self(),
+        };
+
+        acb = bs->drv->bdrv_aio_flush(bs, bdrv_co_io_em_complete, &co);
+        if (acb == NULL) {
+            ret = -EIO;
+        } else {
+            qemu_coroutine_yield();
+            ret = co.ret;
+        }
+    } else {
+        /*
+         * Some block drivers always operate in either writethrough or unsafe
+         * mode and don't support bdrv_flush therefore. Usually qemu doesn't
+         * know how the server works (because the behaviour is hardcoded or
+         * depends on server-side configuration), so we can't ensure that
+         * everything is safe on disk. Returning an error doesn't work because
+         * that would break guests even if the server operates in writethrough
+         * mode.
+         *
+         * Let's hope the user knows what he's doing.
+         */
+        ret = 0;
+    }
+    if (ret < 0) {
+        return ret;
+    }
+
+    /* Now flush the underlying protocol.  It will also have BDRV_O_NO_FLUSH
+     * in the case of cache=unsafe, so there are no useless flushes.
+     */
+flush_parent:
+    return bdrv_co_flush(bs->file);
+}
+
+int bdrv_flush(BlockDriverState *bs)
+{
+    Coroutine *co;
+    RwCo rwco = {
+        .bs = bs,
+        .ret = NOT_DONE,
+    };
+
+    if (qemu_in_coroutine()) {
+        /* Fast-path if already in coroutine context */
+        bdrv_flush_co_entry(&rwco);
+    } else {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        co = qemu_coroutine_create(bdrv_flush_co_entry);
+        qemu_coroutine_enter(co, &rwco);
+        while (rwco.ret == NOT_DONE) {
+            aio_poll(aio_context, true);
+        }
+    }
+
+    return rwco.ret;
+}
+
+typedef struct DiscardCo {
+    BlockDriverState *bs;
+    int64_t sector_num;
+    int nb_sectors;
+    int ret;
+} DiscardCo;
+static void coroutine_fn bdrv_discard_co_entry(void *opaque)
+{
+    DiscardCo *rwco = opaque;
+
+    rwco->ret = bdrv_co_discard(rwco->bs, rwco->sector_num, rwco->nb_sectors);
+}
+
+int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
+                                 int nb_sectors)
+{
+    int max_discard, ret;
+
+    if (!bs->drv) {
+        return -ENOMEDIUM;
+    }
+
+    ret = bdrv_check_request(bs, sector_num, nb_sectors);
+    if (ret < 0) {
+        return ret;
+    } else if (bs->read_only) {
+        return -EROFS;
+    }
+
+    bdrv_reset_dirty(bs, sector_num, nb_sectors);
+
+    /* Do nothing if disabled.  */
+    if (!(bs->open_flags & BDRV_O_UNMAP)) {
+        return 0;
+    }
+
+    if (!bs->drv->bdrv_co_discard && !bs->drv->bdrv_aio_discard) {
+        return 0;
+    }
+
+    max_discard = MIN_NON_ZERO(bs->bl.max_discard, BDRV_REQUEST_MAX_SECTORS);
+    while (nb_sectors > 0) {
+        int ret;
+        int num = nb_sectors;
+
+        /* align request */
+        if (bs->bl.discard_alignment &&
+            num >= bs->bl.discard_alignment &&
+            sector_num % bs->bl.discard_alignment) {
+            if (num > bs->bl.discard_alignment) {
+                num = bs->bl.discard_alignment;
+            }
+            num -= sector_num % bs->bl.discard_alignment;
+        }
+
+        /* limit request size */
+        if (num > max_discard) {
+            num = max_discard;
+        }
+
+        if (bs->drv->bdrv_co_discard) {
+            ret = bs->drv->bdrv_co_discard(bs, sector_num, num);
+        } else {
+            BlockAIOCB *acb;
+            CoroutineIOCompletion co = {
+                .coroutine = qemu_coroutine_self(),
+            };
+
+            acb = bs->drv->bdrv_aio_discard(bs, sector_num, nb_sectors,
+                                            bdrv_co_io_em_complete, &co);
+            if (acb == NULL) {
+                return -EIO;
+            } else {
+                qemu_coroutine_yield();
+                ret = co.ret;
+            }
+        }
+        if (ret && ret != -ENOTSUP) {
+            return ret;
+        }
+
+        sector_num += num;
+        nb_sectors -= num;
+    }
+    return 0;
+}
+
+int bdrv_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors)
+{
+    Coroutine *co;
+    DiscardCo rwco = {
+        .bs = bs,
+        .sector_num = sector_num,
+        .nb_sectors = nb_sectors,
+        .ret = NOT_DONE,
+    };
+
+    if (qemu_in_coroutine()) {
+        /* Fast-path if already in coroutine context */
+        bdrv_discard_co_entry(&rwco);
+    } else {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        co = qemu_coroutine_create(bdrv_discard_co_entry);
+        qemu_coroutine_enter(co, &rwco);
+        while (rwco.ret == NOT_DONE) {
+            aio_poll(aio_context, true);
+        }
+    }
+
+    return rwco.ret;
+}
+
+/* needed for generic scsi interface */
+
+int bdrv_ioctl(BlockDriverState *bs, unsigned long int req, void *buf)
+{
+    BlockDriver *drv = bs->drv;
+
+    if (drv && drv->bdrv_ioctl)
+        return drv->bdrv_ioctl(bs, req, buf);
+    return -ENOTSUP;
+}
+
+BlockAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,
+        unsigned long int req, void *buf,
+        BlockCompletionFunc *cb, void *opaque)
+{
+    BlockDriver *drv = bs->drv;
+
+    if (drv && drv->bdrv_aio_ioctl)
+        return drv->bdrv_aio_ioctl(bs, req, buf, cb, opaque);
+    return NULL;
+}
+
+void *qemu_blockalign(BlockDriverState *bs, size_t size)
+{
+    return qemu_memalign(bdrv_opt_mem_align(bs), size);
+}
+
+void *qemu_blockalign0(BlockDriverState *bs, size_t size)
+{
+    return memset(qemu_blockalign(bs, size), 0, size);
+}
+
+void *qemu_try_blockalign(BlockDriverState *bs, size_t size)
+{
+    size_t align = bdrv_opt_mem_align(bs);
+
+    /* Ensure that NULL is never returned on success */
+    assert(align > 0);
+    if (size == 0) {
+        size = align;
+    }
+
+    return qemu_try_memalign(align, size);
+}
+
+void *qemu_try_blockalign0(BlockDriverState *bs, size_t size)
+{
+    void *mem = qemu_try_blockalign(bs, size);
+
+    if (mem) {
+        memset(mem, 0, size);
+    }
+
+    return mem;
+}
+
+/*
+ * Check if all memory in this vector is sector aligned.
+ */
+bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov)
+{
+    int i;
+    size_t alignment = bdrv_opt_mem_align(bs);
+
+    for (i = 0; i < qiov->niov; i++) {
+        if ((uintptr_t) qiov->iov[i].iov_base % alignment) {
+            return false;
+        }
+        if (qiov->iov[i].iov_len % alignment) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+void bdrv_add_before_write_notifier(BlockDriverState *bs,
+                                    NotifierWithReturn *notifier)
+{
+    notifier_with_return_list_add(&bs->before_write_notifiers, notifier);
+}
+
+void bdrv_io_plug(BlockDriverState *bs)
+{
+    BlockDriver *drv = bs->drv;
+    if (drv && drv->bdrv_io_plug) {
+        drv->bdrv_io_plug(bs);
+    } else if (bs->file) {
+        bdrv_io_plug(bs->file);
+    }
+}
+
+void bdrv_io_unplug(BlockDriverState *bs)
+{
+    BlockDriver *drv = bs->drv;
+    if (drv && drv->bdrv_io_unplug) {
+        drv->bdrv_io_unplug(bs);
+    } else if (bs->file) {
+        bdrv_io_unplug(bs->file);
+    }
+}
+
+void bdrv_flush_io_queue(BlockDriverState *bs)
+{
+    BlockDriver *drv = bs->drv;
+    if (drv && drv->bdrv_flush_io_queue) {
+        drv->bdrv_flush_io_queue(bs);
+    } else if (bs->file) {
+        bdrv_flush_io_queue(bs->file);
+    }
+}