From c9362e8c14bc511d472306c419d2d14b1807b948 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Mon, 15 Nov 2010 17:16:31 -0200 Subject: [RHEL6 qemu-kvm PATCH 02/21] Add cache=unsafe parameter to -drive RH-Author: Kevin Wolf Message-id: <1289841395-30386-3-git-send-email-kwolf@redhat.com> Patchwork-id: 13564 O-Subject: [RHEL-6.1 qemu-kvm PATCH 2/6] Add cache=unsafe parameter to -drive Bugzilla: 653536 RH-Acked-by: Amit Shah RH-Acked-by: Jes Sorensen RH-Acked-by: Christoph Hellwig Bugzilla: 653536 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 Signed-off-by: Aurelien Jarno (cherry picked from commit 016f5cf6ff465411733878a17c8f8febb7668321) Conflicts: qemu-options.hx Signed-off-by: Kevin Wolf --- block.c | 29 +++++++++++++++++++++++++++++ block.h | 1 + qemu-config.c | 2 +- qemu-options.hx | 12 +++++++++--- vl.c | 3 +++ 5 files changed, 43 insertions(+), 4 deletions(-) Signed-off-by: Eduardo Habkost --- block.c | 29 +++++++++++++++++++++++++++++ block.h | 1 + qemu-config.c | 2 +- qemu-options.hx | 12 +++++++++--- vl.c | 3 +++ 5 files changed, 43 insertions(+), 4 deletions(-) diff --git a/block.c b/block.c index a575111..394af13 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, @@ -1352,6 +1354,10 @@ 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); } @@ -2152,6 +2158,10 @@ 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); @@ -2266,6 +2276,25 @@ 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 */ diff --git a/block.h b/block.h index 9b08d07..42ac5ae 100644 --- a/block.h +++ b/block.h @@ -32,6 +32,7 @@ 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 04c7a4d..45882d4 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 f77439b..ee42a31 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -102,8 +102,8 @@ 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]\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") DEF("set", HAS_ARG, QEMU_OPTION_set, @@ -139,7 +139,7 @@ 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} @@ -171,6 +171,12 @@ 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 diff --git a/vl.c b/vl.c index d19a3e9..5014a5a 100644 --- a/vl.c +++ b/vl.c @@ -2322,6 +2322,9 @@ 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 { -- 1.7.3.2