@@ -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,
@@ -1306,6 +1308,10 @@ 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);
}
@@ -2082,6 +2088,10 @@ 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);
@@ -33,6 +33,7 @@ typedef struct QEMUSnapshotInfo {
#define BDRV_O_CACHE_WB 0x0040 /* 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_FLUSH 0x0200 /* disable flushing on this disk */
#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)
@@ -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, volatile)",
},{
.name = "aio",
.type = QEMU_OPT_STRING,
@@ -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|volatile|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 snapshot=@var{snapshot}
@var{snapshot} is "on" or "off" and allows to enable snapshot for given drive (see @option{-snapshot}).
@item cache=@var{cache}
-@var{cache} is "none", "writeback", or "writethrough" and controls how the host cache is used to access block data.
+@var{cache} is "none", "writeback", "volatile", or "writethrough" and controls how the host cache is used to access block data.
@item aio=@var{aio}
@var{aio} is "threads", or "native" and selects between pthread based disk I/O and native Linux AIO.
@item format=@var{format}
@@ -913,6 +913,9 @@ DriveInfo *drive_init(QemuOpts *opts, void *opaque,
bdrv_flags |= BDRV_O_NOCACHE;
} else if (!strcmp(buf, "writeback")) {
bdrv_flags |= BDRV_O_CACHE_WB;
+ } else if (!strcmp(buf, "volatile")) {
+ bdrv_flags |= BDRV_O_CACHE_WB;
+ bdrv_flags |= BDRV_O_NO_FLUSH;
} else if (!strcmp(buf, "writethrough")) {
/* this is the default */
} else {
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 "volatile", as guest data is not guaranteed to survive host crashes anymore. Signed-off-by: Alexander Graf <agraf@suse.de> --- block.c | 10 ++++++++++ block.h | 1 + qemu-config.c | 2 +- qemu-options.hx | 7 ++++--- vl.c | 3 +++ 5 files changed, 19 insertions(+), 4 deletions(-)