diff options
| -rw-r--r-- | block.c | 29 | ||||
| -rw-r--r-- | block.h | 1 | ||||
| -rw-r--r-- | qemu-config.c | 2 | ||||
| -rw-r--r-- | qemu-options.hx | 13 | ||||
| -rw-r--r-- | vl.c | 3 |
5 files changed, 44 insertions, 4 deletions
@@ -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 */ @@ -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) diff --git a/qemu-config.c b/qemu-config.c index aa376d450a..5a4e61b0f6 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 03e95fd2bf..cea9b72b2a 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 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", "unsafe", 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} @@ -180,6 +181,12 @@ Some block drivers perform badly with @option{cache=writethrough}, most notably, qcow2. If performance is more important than correctness, @option{cache=writeback} should be used with qcow2. +In case you don't care about data integrity over host failures, use +cache=unsafe. This option tells qemu that it never needs to write any data +to the disk but can instead keeps things in cache. If anything goes wrong, +like your host losing power, the disk storage getting disconnected accidently, +etc. you're image will most probably be rendered unusable. + Instead of @option{-cdrom} you can use: @example qemu -drive file=file,index=2,media=cdrom @@ -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, "unsafe")) { + bdrv_flags |= BDRV_O_CACHE_WB; + bdrv_flags |= BDRV_O_NO_FLUSH; } else if (!strcmp(buf, "writethrough")) { /* this is the default */ } else { |