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authorStefan Hajnoczi <stefanha@linux.vnet.ibm.com>2011-08-04 12:26:52 +0100
committerKevin Wolf <kwolf@redhat.com>2011-08-23 14:15:17 +0200
commit92196b2f5664d5defa778b1b24df56e2239b5e93 (patch)
tree944fe6b4fb403578fdb43073ce622ef0a34befc6 /block.c
parentc3993cdca39c252d65bbbcc234d8d242dc9bd693 (diff)
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block: add cache=directsync parameter to -drive
This patch adds -drive cache=directsync for O_DIRECT | O_SYNC host file I/O with no disk write cache presented to the guest. This mode is useful when guests may not be sending flushes when appropriate and therefore leave data at risk in case of power failure. When cache=directsync is used, write operations are only completed to the guest when data is safely on disk. This new mode is like cache=writethrough but it bypasses the host page cache. Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'block.c')
-rw-r--r--block.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/block.c b/block.c
index dbef3ae..4186a2f 100644
--- a/block.c
+++ b/block.c
@@ -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);
}