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Re: [Qemu-devel] [PATCH] qcow2: make cache=unsafe usable
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH] qcow2: make cache=unsafe usable |
Date: |
Wed, 07 Sep 2011 11:56:22 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0 |
Am 07.09.2011 11:24, schrieb Avi Kivity:
> Currently cache=unsafe is unsafe to the point of unusability - the
> caches are never written to disk except on exit so anything except
> an orderly exit -- including live migration -- leaves the disk image
> corrupted.
>
> Fix by interpreting flush requests and doing everything except flushing
> the underlying file. The contents of the metadata cache are transferred
> to the host pagecache, so that qemu aborts keep the disk in a consistent
> state, and live migration (on the same host, or if using a coherent
> filesystem) works.
>
> Signed-off-by: Avi Kivity <address@hidden>
> ---
>
> Untested - is this the right approach?
Hm, could work, even though I don't like it very much. The alternative
approach would be something like this (not only untested, but won't even
compile):
diff --git a/block.c b/block.c
index a8c789a..1aa5967 100644
--- a/block.c
+++ b/block.c
@@ -1723,10 +1723,6 @@ const char *bdrv_get_device_name(BlockDriverState
*bs)
int bdrv_flush(BlockDriverState *bs)
{
- if (bs->open_flags & BDRV_O_NO_FLUSH) {
- return 0;
- }
-
if (bs->drv && bdrv_has_async_flush(bs->drv) && qemu_in_coroutine()) {
return bdrv_co_flush_em(bs);
}
@@ -2624,10 +2620,6 @@ BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState
*bs,
trace_bdrv_aio_flush(bs, opaque);
- 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);
diff --git a/block/raw-posix.c b/block/raw-posix.c
index bcf50b2..bb0c0c5 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -629,6 +629,10 @@ static BlockDriverAIOCB
*raw_aio_flush(BlockDriverState *bs,
{
BDRVRawState *s = bs->opaque;
+ if (bs->open_flags & BDRV_O_NO_FLUSH) {
+ return bdrv_aio_noop_em(bs, cb, opaque);
+ }
+
if (fd_open(bs) < 0)
return NULL;
@@ -839,6 +843,11 @@ static int raw_create(const char *filename,
QEMUOptionParameter *options)
static int raw_flush(BlockDriverState *bs)
{
BDRVRawState *s = bs->opaque;
+
+ if (bs->open_flags & BDRV_O_NO_FLUSH) {
+ return 0;
+ }
+
return qemu_fdatasync(s->fd);
}