On 05/26/2010 10:51 AM, Alexander Graf wrote:
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 Grafag...@suse.de
I'm happy merging this for now, but I think it might make more sense to
do this as per-device flush control qdev options since those bits are
actually guest visible. Christoph, does that seem reasonable?
Regards,
Anthony Liguori
---
v2 - v3:
- Add description of cache=volatile
- Squash aio noop noop patch into this one
v3 - v4:
- Rename cache=volatile to cache=unsafe
---
block.c | 28
block.h |1 +
qemu-config.c |2 +-
qemu-options.hx | 13 ++---
vl.c|3 +++
5 files changed, 43 insertions(+), 4 deletions(-)
diff --git a/block.c b/block.c
index 0b0966c..3c0249b 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 +2224,24 @@ static BlockDriverAIOCB
*bdrv_aio_flush_em(BlockDriverState *bs,
returnacb-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 hadler */
+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);
+returnacb-common;
+}
+
/**/
/* sync block device emulation */
diff --git a/block.h b/block.h
index 278259c..24efeb6 100644
--- a/block.h
+++ b/block.h
@@ -33,6 +33,7 @@ typedef struct QEMUSnapshotInfo {
#define BDRV_O_CACHE_WB0x0040 /* use write-back caching */
#define BDRV_O_NATIVE_AIO 0x0080 /* use native AIO instead of the thread
pool */
#define BDRV_O_NO_BACKING 0x0100 /* don't open the backing file */
+#define BDRV_O_NO_FLUSH0x0200 /* disable flushing on this disk */
#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)
diff --git a/qemu-config.c b/qemu-config.c
index aa376d4..5a4e61b 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -54,7 +54,7 @@ QemuOptsList qemu_drive_opts = {
},{
.name = cache,
.type = QEMU_OPT_STRING,
-.help = host cache usage (none, writeback, writethrough),
+.help = host cache usage (none, writeback, writethrough, unsafe),
},{
.name = aio,
.type = QEMU_OPT_STRING,
diff --git a/qemu-options.hx b/qemu-options.hx
index 03e95fd..cea9b72 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -118,8 +118,9 @@ ETEXI
DEF(drive, HAS_ARG, QEMU_OPTION_drive,
-drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n
[,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n
- [,cache=writethrough|writeback|none][,format=f][,serial=s]\n
- [,addr=A][,id=name][,aio=threads|native][,readonly=on|off]\n
+ [,cache=writethrough|writeback|unsafe|none][,format=f]\n
+ [,serial=s][,addr=A][,id=name][,aio=threads|native]\n
+ [,readonly=on|off]\n
use 'file' as a drive image\n, QEMU_ARCH_ALL)
STEXI
@item -drive @var{option}[,@var{option}[,@var{option}[,...]]]
@@ -148,7 +149,7 @@ These options have the same definition as they have in
@option{-hdachs}.
@item snapsh...@var{snapshot}
