Add cache=unsafe parameter to -drive

Usually the guest can tell the host to flush data to disk. In some cases we
don't want to flush though, but try to keep everything in cache.

So let's add a new cache value to -drive that allows us to set the cache
policy to most aggressive, disabling flushes. We call this mode "unsafe",
as guest data is not guaranteed to survive host crashes anymore.

This patch also adds a noop function for aio, so we can do nothing in AIO
fashion.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 29 insertions, 0 deletions

diff --git a/block.c b/block.c
index 0b0966c571..cd70730a3e 100644
--- a/block.c
+++ b/block.c
@@ -50,6 +50,8 @@ static BlockDriverAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,
         BlockDriverCompletionFunc *cb, void *opaque);
 static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
         BlockDriverCompletionFunc *cb, void *opaque);
+static BlockDriverAIOCB *bdrv_aio_noop_em(BlockDriverState *bs,
+        BlockDriverCompletionFunc *cb, void *opaque);
 static int bdrv_read_em(BlockDriverState *bs, int64_t sector_num,
                         uint8_t *buf, int nb_sectors);
 static int bdrv_write_em(BlockDriverState *bs, int64_t sector_num,
@@ -1312,6 +1314,10 @@ const char *bdrv_get_device_name(BlockDriverState *bs)
 
 void bdrv_flush(BlockDriverState *bs)
 {
+    if (bs->open_flags & BDRV_O_NO_FLUSH) {
+        return;
+    }
+
     if (bs->drv && bs->drv->bdrv_flush)
         bs->drv->bdrv_flush(bs);
 }
@@ -2099,6 +2105,10 @@ BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState *bs,
 {
     BlockDriver *drv = bs->drv;
 
+    if (bs->open_flags & BDRV_O_NO_FLUSH) {
+        return bdrv_aio_noop_em(bs, cb, opaque);
+    }
+
     if (!drv)
         return NULL;
     return drv->bdrv_aio_flush(bs, cb, opaque);
@@ -2214,6 +2224,25 @@ static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
     return &acb->common;
 }
 
+static BlockDriverAIOCB *bdrv_aio_noop_em(BlockDriverState *bs,
+        BlockDriverCompletionFunc *cb, void *opaque)
+{
+    BlockDriverAIOCBSync *acb;
+
+    acb = qemu_aio_get(&bdrv_em_aio_pool, bs, cb, opaque);
+    acb->is_write = 1; /* don't bounce in the completion handler */
+    acb->qiov = NULL;
+    acb->bounce = NULL;
+    acb->ret = 0;
+
+    if (!acb->bh) {
+        acb->bh = qemu_bh_new(bdrv_aio_bh_cb, acb);
+    }
+
+    qemu_bh_schedule(acb->bh);
+    return &acb->common;
+}
+
 /**************************************************************/
 /* sync block device emulation */