block: introduce preallocate filter

It's intended to be inserted between format and protocol nodes to
preallocate additional space (expanding protocol file) on writes
crossing EOF. It improves performance for file-systems with slow
allocation.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201021145859.11201-9-vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
[mreitz: Two comment fixes, and bumped the version from 5.2 to 6.0]
Signed-off-by: Max Reitz <mreitz@redhat.com>

2 files changed, 560 insertions, 0 deletions

diff --git a/block/meson.build b/block/meson.build
index 5dcc1e5cce..7595d86c41 100644
--- a/block/meson.build
+++ b/block/meson.build
@@ -12,6 +12,7 @@ block_ss.add(files(
   'block-copy.c',
   'commit.c',
   'copy-on-read.c',
+  'preallocate.c',
   'create.c',
   'crypto.c',
   'dirty-bitmap.c',
diff --git a/block/preallocate.c b/block/preallocate.c
new file mode 100644
index 0000000000..b619206304
--- /dev/null
+++ b/block/preallocate.c
@@ -0,0 +1,559 @@
+/*
+ * preallocate filter driver
+ *
+ * The driver performs preallocate operation: it is injected above
+ * some node, and before each write over EOF it does additional preallocating
+ * write-zeroes request.
+ *
+ * Copyright (c) 2020 Virtuozzo International GmbH.
+ *
+ * Author:
+ *  Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+
+#include "qapi/error.h"
+#include "qemu/module.h"
+#include "qemu/option.h"
+#include "qemu/units.h"
+#include "block/block_int.h"
+
+
+typedef struct PreallocateOpts {
+    int64_t prealloc_size;
+    int64_t prealloc_align;
+} PreallocateOpts;
+
+typedef struct BDRVPreallocateState {
+    PreallocateOpts opts;
+
+    /*
+     * Track real data end, to crop preallocation on close. If < 0 the status is
+     * unknown.
+     *
+     * @data_end is a maximum of file size on open (or when we get write/resize
+     * permissions) and all write request ends after it. So it's safe to
+     * truncate to data_end if it is valid.
+     */
+    int64_t data_end;
+
+    /*
+     * Start of trailing preallocated area which reads as zero. May be smaller
+     * than data_end, if user does over-EOF write zero operation. If < 0 the
+     * status is unknown.
+     *
+     * If both @zero_start and @file_end are valid, the region
+     * [@zero_start, @file_end) is known to be preallocated zeroes. If @file_end
+     * is not valid, @zero_start doesn't make much sense.
+     */
+    int64_t zero_start;
+
+    /*
+     * Real end of file. Actually the cache for bdrv_getlength(bs->file->bs),
+     * to avoid extra lseek() calls on each write operation. If < 0 the status
+     * is unknown.
+     */
+    int64_t file_end;
+
+    /*
+     * All three states @data_end, @zero_start and @file_end are guaranteed to
+     * be invalid (< 0) when we don't have both exclusive BLK_PERM_RESIZE and
+     * BLK_PERM_WRITE permissions on file child.
+     */
+} BDRVPreallocateState;
+
+#define PREALLOCATE_OPT_PREALLOC_ALIGN "prealloc-align"
+#define PREALLOCATE_OPT_PREALLOC_SIZE "prealloc-size"
+static QemuOptsList runtime_opts = {
+    .name = "preallocate",
+    .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
+    .desc = {
+        {
+            .name = PREALLOCATE_OPT_PREALLOC_ALIGN,
+            .type = QEMU_OPT_SIZE,
+            .help = "on preallocation, align file length to this number, "
+                "default 1M",
+        },
+        {
+            .name = PREALLOCATE_OPT_PREALLOC_SIZE,
+            .type = QEMU_OPT_SIZE,
+            .help = "how much to preallocate, default 128M",
+        },
+        { /* end of list */ }
+    },
+};
+
+static bool preallocate_absorb_opts(PreallocateOpts *dest, QDict *options,
+                                    BlockDriverState *child_bs, Error **errp)
+{
+    QemuOpts *opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
+
+    if (!qemu_opts_absorb_qdict(opts, options, errp)) {
+        return false;
+    }
+
+    dest->prealloc_align =
+        qemu_opt_get_size(opts, PREALLOCATE_OPT_PREALLOC_ALIGN, 1 * MiB);
+    dest->prealloc_size =
+        qemu_opt_get_size(opts, PREALLOCATE_OPT_PREALLOC_SIZE, 128 * MiB);
+
+    qemu_opts_del(opts);
+
+    if (!QEMU_IS_ALIGNED(dest->prealloc_align, BDRV_SECTOR_SIZE)) {
+        error_setg(errp, "prealloc-align parameter of preallocate filter "
+                   "is not aligned to %llu", BDRV_SECTOR_SIZE);
+        return false;
+    }
+
+    if (!QEMU_IS_ALIGNED(dest->prealloc_align,
+                         child_bs->bl.request_alignment)) {
+        error_setg(errp, "prealloc-align parameter of preallocate filter "
+                   "is not aligned to underlying node request alignment "
+                   "(%" PRIi32 ")", child_bs->bl.request_alignment);
+        return false;
+    }
+
+    return true;
+}
+
+static int preallocate_open(BlockDriverState *bs, QDict *options, int flags,
+                            Error **errp)
+{
+    BDRVPreallocateState *s = bs->opaque;
+
+    /*
+     * s->data_end and friends should be initialized on permission update.
+     * For this to work, mark them invalid.
+     */
+    s->file_end = s->zero_start = s->data_end = -EINVAL;
+
+    bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
+                               BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
+                               false, errp);
+    if (!bs->file) {
+        return -EINVAL;
+    }
+
+    if (!preallocate_absorb_opts(&s->opts, options, bs->file->bs, errp)) {
+        return -EINVAL;
+    }
+
+    bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
+        (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
+
+    bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
+        ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
+            bs->file->bs->supported_zero_flags);
+
+    return 0;
+}
+
+static void preallocate_close(BlockDriverState *bs)
+{
+    int ret;
+    BDRVPreallocateState *s = bs->opaque;
+
+    if (s->data_end < 0) {
+        return;
+    }
+
+    if (s->file_end < 0) {
+        s->file_end = bdrv_getlength(bs->file->bs);
+        if (s->file_end < 0) {
+            return;
+        }
+    }
+
+    if (s->data_end < s->file_end) {
+        ret = bdrv_truncate(bs->file, s->data_end, true, PREALLOC_MODE_OFF, 0,
+                            NULL);
+        s->file_end = ret < 0 ? ret : s->data_end;
+    }
+}
+
+
+/*
+ * Handle reopen.
+ *
+ * We must implement reopen handlers, otherwise reopen just don't work. Handle
+ * new options and don't care about preallocation state, as it is handled in
+ * set/check permission handlers.
+ */
+
+static int preallocate_reopen_prepare(BDRVReopenState *reopen_state,
+                                      BlockReopenQueue *queue, Error **errp)
+{
+    PreallocateOpts *opts = g_new0(PreallocateOpts, 1);
+
+    if (!preallocate_absorb_opts(opts, reopen_state->options,
+                                 reopen_state->bs->file->bs, errp)) {
+        g_free(opts);
+        return -EINVAL;
+    }
+
+    reopen_state->opaque = opts;
+
+    return 0;
+}
+
+static void preallocate_reopen_commit(BDRVReopenState *state)
+{
+    BDRVPreallocateState *s = state->bs->opaque;
+
+    s->opts = *(PreallocateOpts *)state->opaque;
+
+    g_free(state->opaque);
+    state->opaque = NULL;
+}
+
+static void preallocate_reopen_abort(BDRVReopenState *state)
+{
+    g_free(state->opaque);
+    state->opaque = NULL;
+}
+
+static coroutine_fn int preallocate_co_preadv_part(
+        BlockDriverState *bs, uint64_t offset, uint64_t bytes,
+        QEMUIOVector *qiov, size_t qiov_offset, int flags)
+{
+    return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
+                               flags);
+}
+
+static int coroutine_fn preallocate_co_pdiscard(BlockDriverState *bs,
+                                               int64_t offset, int bytes)
+{
+    return bdrv_co_pdiscard(bs->file, offset, bytes);
+}
+
+static bool can_write_resize(uint64_t perm)
+{
+    return (perm & BLK_PERM_WRITE) && (perm & BLK_PERM_RESIZE);
+}
+
+static bool has_prealloc_perms(BlockDriverState *bs)
+{
+    BDRVPreallocateState *s = bs->opaque;
+
+    if (can_write_resize(bs->file->perm)) {
+        assert(!(bs->file->shared_perm & BLK_PERM_WRITE));
+        assert(!(bs->file->shared_perm & BLK_PERM_RESIZE));
+        return true;
+    }
+
+    assert(s->data_end < 0);
+    assert(s->zero_start < 0);
+    assert(s->file_end < 0);
+    return false;
+}
+
+/*
+ * Call on each write. Returns true if @want_merge_zero is true and the region
+ * [offset, offset + bytes) is zeroed (as a result of this call or earlier
+ * preallocation).
+ *
+ * want_merge_zero is used to merge write-zero request with preallocation in
+ * one bdrv_co_pwrite_zeroes() call.
+ */
+static bool coroutine_fn handle_write(BlockDriverState *bs, int64_t offset,
+                                      int64_t bytes, bool want_merge_zero)
+{
+    BDRVPreallocateState *s = bs->opaque;
+    int64_t end = offset + bytes;
+    int64_t prealloc_start, prealloc_end;
+    int ret;
+
+    if (!has_prealloc_perms(bs)) {
+        /* We don't have state neither should try to recover it */
+        return false;
+    }
+
+    if (s->data_end < 0) {
+        s->data_end = bdrv_getlength(bs->file->bs);
+        if (s->data_end < 0) {
+            return false;
+        }
+
+        if (s->file_end < 0) {
+            s->file_end = s->data_end;
+        }
+    }
+
+    if (end <= s->data_end) {
+        return false;
+    }
+
+    /* We have valid s->data_end, and request writes beyond it. */
+
+    s->data_end = end;
+    if (s->zero_start < 0 || !want_merge_zero) {
+        s->zero_start = end;
+    }
+
+    if (s->file_end < 0) {
+        s->file_end = bdrv_getlength(bs->file->bs);
+        if (s->file_end < 0) {
+            return false;
+        }
+    }
+
+    /* Now s->data_end, s->zero_start and s->file_end are valid. */
+
+    if (end <= s->file_end) {
+        /* No preallocation needed. */
+        return want_merge_zero && offset >= s->zero_start;
+    }
+
+    /* Now we want new preallocation, as request writes beyond s->file_end. */
+
+    prealloc_start = want_merge_zero ? MIN(offset, s->file_end) : s->file_end;
+    prealloc_end = QEMU_ALIGN_UP(end + s->opts.prealloc_size,
+                                 s->opts.prealloc_align);
+
+    ret = bdrv_co_pwrite_zeroes(
+            bs->file, prealloc_start, prealloc_end - prealloc_start,
+            BDRV_REQ_NO_FALLBACK | BDRV_REQ_SERIALISING | BDRV_REQ_NO_WAIT);
+    if (ret < 0) {
+        s->file_end = ret;
+        return false;
+    }
+
+    s->file_end = prealloc_end;
+    return want_merge_zero;
+}
+
+static int coroutine_fn preallocate_co_pwrite_zeroes(BlockDriverState *bs,
+        int64_t offset, int bytes, BdrvRequestFlags flags)
+{
+    bool want_merge_zero =
+        !(flags & ~(BDRV_REQ_ZERO_WRITE | BDRV_REQ_NO_FALLBACK));
+    if (handle_write(bs, offset, bytes, want_merge_zero)) {
+        return 0;
+    }
+
+    return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
+}
+
+static coroutine_fn int preallocate_co_pwritev_part(BlockDriverState *bs,
+                                                    uint64_t offset,
+                                                    uint64_t bytes,
+                                                    QEMUIOVector *qiov,
+                                                    size_t qiov_offset,
+                                                    int flags)
+{
+    handle_write(bs, offset, bytes, false);
+
+    return bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset,
+                                flags);
+}
+
+static int coroutine_fn
+preallocate_co_truncate(BlockDriverState *bs, int64_t offset,
+                        bool exact, PreallocMode prealloc,
+                        BdrvRequestFlags flags, Error **errp)
+{
+    ERRP_GUARD();
+    BDRVPreallocateState *s = bs->opaque;
+    int ret;
+
+    if (s->data_end >= 0 && offset > s->data_end) {
+        if (s->file_end < 0) {
+            s->file_end = bdrv_getlength(bs->file->bs);
+            if (s->file_end < 0) {
+                error_setg(errp, "failed to get file length");
+                return s->file_end;
+            }
+        }
+
+        if (prealloc == PREALLOC_MODE_FALLOC) {
+            /*
+             * If offset <= s->file_end, the task is already done, just
+             * update s->data_end, to move part of "filter preallocation"
+             * to "preallocation requested by user".
+             * Otherwise just proceed to preallocate missing part.
+             */
+            if (offset <= s->file_end) {
+                s->data_end = offset;
+                return 0;
+            }
+        } else {
+            /*
+             * We have to drop our preallocation, to
+             * - avoid "Cannot use preallocation for shrinking files" in
+             *   case of offset < file_end
+             * - give PREALLOC_MODE_OFF a chance to keep small disk
+             *   usage
+             * - give PREALLOC_MODE_FULL a chance to actually write the
+             *   whole region as user expects
+             */
+            if (s->file_end > s->data_end) {
+                ret = bdrv_co_truncate(bs->file, s->data_end, true,
+                                       PREALLOC_MODE_OFF, 0, errp);
+                if (ret < 0) {
+                    s->file_end = ret;
+                    error_prepend(errp, "preallocate-filter: failed to drop "
+                                  "write-zero preallocation: ");
+                    return ret;
+                }
+                s->file_end = s->data_end;
+            }
+        }
+
+        s->data_end = offset;
+    }
+
+    ret = bdrv_co_truncate(bs->file, offset, exact, prealloc, flags, errp);
+    if (ret < 0) {
+        s->file_end = s->zero_start = s->data_end = ret;
+        return ret;
+    }
+
+    if (has_prealloc_perms(bs)) {
+        s->file_end = s->zero_start = s->data_end = offset;
+    }
+    return 0;
+}
+
+static int coroutine_fn preallocate_co_flush(BlockDriverState *bs)
+{
+    return bdrv_co_flush(bs->file->bs);
+}
+
+static int64_t preallocate_getlength(BlockDriverState *bs)
+{
+    int64_t ret;
+    BDRVPreallocateState *s = bs->opaque;
+
+    if (s->data_end >= 0) {
+        return s->data_end;
+    }
+
+    ret = bdrv_getlength(bs->file->bs);
+
+    if (has_prealloc_perms(bs)) {
+        s->file_end = s->zero_start = s->data_end = ret;
+    }
+
+    return ret;
+}
+
+static int preallocate_check_perm(BlockDriverState *bs,
+                                  uint64_t perm, uint64_t shared, Error **errp)
+{
+    BDRVPreallocateState *s = bs->opaque;
+
+    if (s->data_end >= 0 && !can_write_resize(perm)) {
+        /*
+         * Lose permissions.
+         * We should truncate in check_perm, as in set_perm bs->file->perm will
+         * be already changed, and we should not violate it.
+         */
+        if (s->file_end < 0) {
+            s->file_end = bdrv_getlength(bs->file->bs);
+            if (s->file_end < 0) {
+                error_setg(errp, "Failed to get file length");
+                return s->file_end;
+            }
+        }
+
+        if (s->data_end < s->file_end) {
+            int ret = bdrv_truncate(bs->file, s->data_end, true,
+                                    PREALLOC_MODE_OFF, 0, NULL);
+            if (ret < 0) {
+                error_setg(errp, "Failed to drop preallocation");
+                s->file_end = ret;
+                return ret;
+            }
+            s->file_end = s->data_end;
+        }
+    }
+
+    return 0;
+}
+
+static void preallocate_set_perm(BlockDriverState *bs,
+                                 uint64_t perm, uint64_t shared)
+{
+    BDRVPreallocateState *s = bs->opaque;
+
+    if (can_write_resize(perm)) {
+        if (s->data_end < 0) {
+            s->data_end = s->file_end = s->zero_start =
+                bdrv_getlength(bs->file->bs);
+        }
+    } else {
+        /*
+         * We drop our permissions, as well as allow shared
+         * permissions (see preallocate_child_perm), anyone will be able to
+         * change the child, so mark all states invalid. We'll regain control if
+         * get good permissions back.
+         */
+        s->data_end = s->file_end = s->zero_start = -EINVAL;
+    }
+}
+
+static void preallocate_child_perm(BlockDriverState *bs, BdrvChild *c,
+    BdrvChildRole role, BlockReopenQueue *reopen_queue,
+    uint64_t perm, uint64_t shared, uint64_t *nperm, uint64_t *nshared)
+{
+    bdrv_default_perms(bs, c, role, reopen_queue, perm, shared, nperm, nshared);
+
+    if (can_write_resize(perm)) {
+        /* This should come by default, but let's enforce: */
+        *nperm |= BLK_PERM_WRITE | BLK_PERM_RESIZE;
+
+        /*
+         * Don't share, to keep our states s->file_end, s->data_end and
+         * s->zero_start valid.
+         */
+        *nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
+    }
+}
+
+BlockDriver bdrv_preallocate_filter = {
+    .format_name = "preallocate",
+    .instance_size = sizeof(BDRVPreallocateState),
+
+    .bdrv_getlength = preallocate_getlength,
+    .bdrv_open = preallocate_open,
+    .bdrv_close = preallocate_close,
+
+    .bdrv_reopen_prepare  = preallocate_reopen_prepare,
+    .bdrv_reopen_commit   = preallocate_reopen_commit,
+    .bdrv_reopen_abort    = preallocate_reopen_abort,
+
+    .bdrv_co_preadv_part = preallocate_co_preadv_part,
+    .bdrv_co_pwritev_part = preallocate_co_pwritev_part,
+    .bdrv_co_pwrite_zeroes = preallocate_co_pwrite_zeroes,
+    .bdrv_co_pdiscard = preallocate_co_pdiscard,
+    .bdrv_co_flush = preallocate_co_flush,
+    .bdrv_co_truncate = preallocate_co_truncate,
+
+    .bdrv_check_perm = preallocate_check_perm,
+    .bdrv_set_perm = preallocate_set_perm,
+    .bdrv_child_perm = preallocate_child_perm,
+
+    .has_variable_length = true,
+    .is_filter = true,
+};
+
+static void bdrv_preallocate_init(void)
+{
+    bdrv_register(&bdrv_preallocate_filter);
+}
+
+block_init(bdrv_preallocate_init);