diff options
| -rw-r--r-- | block.c | 6 | ||||
| -rw-r--r-- | qemu-config.c | 3 | ||||
| -rw-r--r-- | qemu-img.c | 3 | ||||
| -rw-r--r-- | qemu-options.hx | 8 |
4 files changed, 14 insertions, 6 deletions
@@ -448,6 +448,8 @@ int bdrv_parse_cache_flags(const char *mode, int *flags) if (!strcmp(mode, "off") || !strcmp(mode, "none")) { *flags |= BDRV_O_NOCACHE | BDRV_O_CACHE_WB; + } else if (!strcmp(mode, "directsync")) { + *flags |= BDRV_O_NOCACHE; } else if (!strcmp(mode, "writeback")) { *flags |= BDRV_O_CACHE_WB; } else if (!strcmp(mode, "unsafe")) { @@ -1188,8 +1190,8 @@ int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset, return ret; } - /* No flush needed for cache=writethrough, it uses O_DSYNC */ - if ((bs->open_flags & BDRV_O_CACHE_MASK) != 0) { + /* No flush needed for cache modes that use O_DSYNC */ + if ((bs->open_flags & BDRV_O_CACHE_WB) != 0) { bdrv_flush(bs); } diff --git a/qemu-config.c b/qemu-config.c index 1eb6b9a709..139e07768b 100644 --- a/qemu-config.c +++ b/qemu-config.c @@ -55,7 +55,8 @@ static QemuOptsList qemu_drive_opts = { },{ .name = "cache", .type = QEMU_OPT_STRING, - .help = "host cache usage (none, writeback, writethrough, unsafe)", + .help = "host cache usage (none, writeback, writethrough, " + "directsync, unsafe)", },{ .name = "aio", .type = QEMU_OPT_STRING, diff --git a/qemu-img.c b/qemu-img.c index 5e203c231f..10a3a8bb52 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -66,7 +66,8 @@ static void help(void) " 'filename' is a disk image filename\n" " 'fmt' is the disk image format. It is guessed automatically in most cases\n" " 'cache' is the cache mode used to write the output disk image, the valid\n" - " options are: 'none', 'writeback' (default), 'writethrough' and 'unsafe'\n" + " options are: 'none', 'writeback' (default), 'writethrough', 'directsync'\n" + " and 'unsafe'\n" " 'size' is the disk image size in bytes. Optional suffixes\n" " 'k' or 'K' (kilobyte, 1024), 'M' (megabyte, 1024k), 'G' (gigabyte, 1024M)\n" " and T (terabyte, 1024G) are supported. 'b' is ignored.\n" diff --git a/qemu-options.hx b/qemu-options.hx index d86815dc04..35d95d1d89 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -133,7 +133,7 @@ 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|unsafe][,format=f]\n" + " [,cache=writethrough|writeback|none|directsync|unsafe][,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) @@ -164,7 +164,7 @@ 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", "unsafe", or "writethrough" and controls how the host cache is used to access block data. +@var{cache} is "none", "writeback", "unsafe", "directsync" 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} @@ -199,6 +199,10 @@ The host page cache can be avoided entirely with @option{cache=none}. This will attempt to do disk IO directly to the guests memory. QEMU may still perform an internal copy of the data. +The host page cache can be avoided while only sending write notifications to +the guest when the data has been reported as written by the storage subsystem +using @option{cache=directsync}. + 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. |