Expand cache= option and use write-through caching by default

This patch changes the cache= option to accept none, writeback, or writethough
to control the host page cache behavior.  By default, writethrough caching is
now used which internally is implemented by using O_DSYNC to open the disk
images.  When using -snapshot, writeback is used by default since data integrity
it not at all an issue.

cache=none has the same behavior as cache=off previously.  The later syntax is
still supported by now deprecated.  I also cleaned up the O_DIRECT
implementation to avoid many of the #ifdefs.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5485 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 4 insertions, 1 deletions

diff --git a/block.h b/block.h
index f012913..72c1c24 100644
--- a/block.h
+++ b/block.h
@@ -47,7 +47,10 @@ typedef struct QEMUSnapshotInfo {
                                      use a disk image format on top of
                                      it (default for
                                      bdrv_file_open()) */
-#define BDRV_O_DIRECT      0x0020
+#define BDRV_O_NOCACHE     0x0020 /* do not use the host page cache */
+#define BDRV_O_CACHE_WB    0x0040 /* use write-back caching */
+
+#define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)
 
 void bdrv_info(void);
 void bdrv_info_stats(void);