[Qemu-devel] [PATCH 02/12] block: clarify the meaning of BDRV_O_NOCACHE

[Kevin Wolf <kwolf@redhat.com>]

From: Christoph Hellwig <hch@lst.de>

Change BDRV_O_NOCACHE to only imply bypassing the host OS file cache,
but no writeback semantics.  All existing callers are changed to also
specify BDRV_O_CACHE_WB to give them writeback semantics.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c           |    8 +-------
 block/qcow2.c     |    2 +-
 block/raw-posix.c |    2 +-
 block/raw-win32.c |   12 ++++++------
 blockdev.c        |    2 +-
 qemu-io.c         |    4 ++--
 qemu-nbd.c        |    2 +-
 7 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/block.c b/block.c
index effa86f..3036a2d 100644
--- a/block.c
+++ b/block.c
@@ -439,13 +439,7 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
     bs->drv = drv;
     bs->opaque = qemu_mallocz(drv->instance_size);
 
-    /*
-     * Yes, BDRV_O_NOCACHE aka O_DIRECT means we have to present a
-     * write cache to the guest.  We do need the fdatasync to flush
-     * out transactions for block allocations, and we maybe have a
-     * volatile write cache in our backing device to deal with.
-     */
-    if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))
+    if (flags & BDRV_O_CACHE_WB)
         bs->enable_write_cache = 1;
 
     /*
diff --git a/block/qcow2.c b/block/qcow2.c
index 75b8bec..db1931b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -229,7 +229,7 @@ static int qcow2_open(BlockDriverState *bs, int flags)
     }
 
     /* alloc L2 table/refcount block cache */
-    writethrough = ((flags & BDRV_O_CACHE_MASK) == 0);
+    writethrough = ((flags & BDRV_O_CACHE_WB) == 0);
     s->l2_table_cache = qcow2_cache_create(bs, L2_CACHE_SIZE, writethrough);
     s->refcount_block_cache = qcow2_cache_create(bs, REFCOUNT_CACHE_SIZE,
         writethrough);
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 6b72470..50428fd 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -154,7 +154,7 @@ static int raw_open_common(BlockDriverState *bs, const char *filename,
      * and O_DIRECT for no caching. */
     if ((bdrv_flags & BDRV_O_NOCACHE))
         s->open_flags |= O_DIRECT;
-    else if (!(bdrv_flags & BDRV_O_CACHE_WB))
+    if (!(bdrv_flags & BDRV_O_CACHE_WB))
         s->open_flags |= O_DSYNC;
 
     s->fd = -1;
diff --git a/block/raw-win32.c b/block/raw-win32.c
index c204a80..56bd719 100644
--- a/block/raw-win32.c
+++ b/block/raw-win32.c
@@ -88,9 +88,9 @@ static int raw_open(BlockDriverState *bs, const char *filename, int flags)
     }
 
     overlapped = FILE_ATTRIBUTE_NORMAL;
-    if ((flags & BDRV_O_NOCACHE))
-        overlapped |= FILE_FLAG_NO_BUFFERING | FILE_FLAG_WRITE_THROUGH;
-    else if (!(flags & BDRV_O_CACHE_WB))
+    if (flags & BDRV_O_NOCACHE)
+        overlapped |= FILE_FLAG_NO_BUFFERING;
+    if (!(flags & BDRV_O_CACHE_WB))
         overlapped |= FILE_FLAG_WRITE_THROUGH;
     s->hfile = CreateFile(filename, access_flags,
                           FILE_SHARE_READ, NULL,
@@ -349,9 +349,9 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
     create_flags = OPEN_EXISTING;
 
     overlapped = FILE_ATTRIBUTE_NORMAL;
-    if ((flags & BDRV_O_NOCACHE))
-        overlapped |= FILE_FLAG_NO_BUFFERING | FILE_FLAG_WRITE_THROUGH;
-    else if (!(flags & BDRV_O_CACHE_WB))
+    if (flags & BDRV_O_NOCACHE)
+        overlapped |= FILE_FLAG_NO_BUFFERING;
+    if (!(flags & BDRV_O_CACHE_WB))
         overlapped |= FILE_FLAG_WRITE_THROUGH;
     s->hfile = CreateFile(filename, access_flags,
                           FILE_SHARE_READ, NULL,
diff --git a/blockdev.c b/blockdev.c
index 6e0eb83..1502575 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -326,7 +326,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
 
     if ((buf = qemu_opt_get(opts, "cache")) != NULL) {
         if (!strcmp(buf, "off") || !strcmp(buf, "none")) {
-            bdrv_flags |= BDRV_O_NOCACHE;
+            bdrv_flags |= BDRV_O_NOCACHE | BDRV_O_CACHE_WB;
         } else if (!strcmp(buf, "writeback")) {
             bdrv_flags |= BDRV_O_CACHE_WB;
         } else if (!strcmp(buf, "unsafe")) {
diff --git a/qemu-io.c b/qemu-io.c
index 4470e49..dd4ebf5 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -1655,7 +1655,7 @@ open_f(int argc, char **argv)
 			flags |= BDRV_O_SNAPSHOT;
 			break;
 		case 'n':
-			flags |= BDRV_O_NOCACHE;
+			flags |= BDRV_O_NOCACHE | BDRV_O_CACHE_WB;
 			break;
 		case 'r':
 			readonly = 1;
@@ -1751,7 +1751,7 @@ int main(int argc, char **argv)
 			flags |= BDRV_O_SNAPSHOT;
 			break;
 		case 'n':
-			flags |= BDRV_O_NOCACHE;
+			flags |= BDRV_O_NOCACHE | BDRV_O_CACHE_WB;
 			break;
 		case 'c':
 			add_user_command(optarg);
diff --git a/qemu-nbd.c b/qemu-nbd.c
index e858033..110d78e 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -238,7 +238,7 @@ int main(int argc, char **argv)
             flags |= BDRV_O_SNAPSHOT;
             break;
         case 'n':
-            flags |= BDRV_O_NOCACHE;
+            flags |= BDRV_O_NOCACHE | BDRV_O_CACHE_WB;
             break;
         case 'b':
             bindto = optarg;
-- 
1.7.5.2