block: Remove BDRV_O_CACHE_WB

The previous patches have successively made blk->enable_write_cache the
true source for the information whether a writethrough mode must be
implemented. The corresponding BDRV_O_CACHE_WB is only useless baggage
we're carrying around, so now's the time to remove it.

At the same time, we remove the 'cache.writeback' option parsing on the
BDS level as the only effect was setting the BDRV_O_CACHE_WB flag.

This change requires test cases that explicitly enabled the option to
drop it. Other than that and the change of the error message when
writethrough is enabled on the BDS level (from "Can't set writethrough
mode" to "doesn't support the option"), there should be no change in
behaviour.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

1 files changed, 2 insertions, 19 deletions

diff --git a/blockdev.c b/blockdev.c
index 7a73726..e50e8ea 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -595,7 +595,6 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
         /* bdrv_open() defaults to the values in bdrv_flags (for compatibility
          * with other callers) rather than what we want as the real defaults.
          * Apply the defaults here instead. */
-        qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_WB, writethrough ? "off" : "on");
         qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_DIRECT, "off");
         qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_NO_FLUSH, "off");
         assert((bdrv_flags & BDRV_O_CACHE_MASK) == 0);
@@ -691,7 +690,6 @@ static BlockDriverState *bds_tree_init(QDict *bs_opts, Error **errp)
     /* bdrv_open() defaults to the values in bdrv_flags (for compatibility
      * with other callers) rather than what we want as the real defaults.
      * Apply the defaults here instead. */
-    qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_WB, "on");
     qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_DIRECT, "off");
     qdict_set_default_str(bs_opts, BDRV_OPT_CACHE_NO_FLUSH, "off");
 
@@ -1779,12 +1777,6 @@ static void external_snapshot_prepare(BlkActionState *common,
         flags |= BDRV_O_NO_BACKING;
     }
 
-    /* There is no BB attached during bdrv_open(), so we can't set a
-     * writethrough mode. bdrv_append() will swap the WCE setting so that the
-     * backing file becomes unconditionally writeback (which is what backing
-     * files should always be) and the new overlay gets the original setting. */
-    flags |= BDRV_O_CACHE_WB;
-
     assert(state->new_bs == NULL);
     ret = bdrv_open(&state->new_bs, new_image_file, snapshot_ref, options,
                     flags, errp);
@@ -2529,7 +2521,6 @@ void qmp_blockdev_change_medium(const char *device, const char *filename,
     BlockBackend *blk;
     BlockDriverState *medium_bs = NULL;
     int bdrv_flags, ret;
-    bool writethrough;
     QDict *options = NULL;
     Error *err = NULL;
 
@@ -2548,12 +2539,6 @@ void qmp_blockdev_change_medium(const char *device, const char *filename,
     bdrv_flags &= ~(BDRV_O_TEMPORARY | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING |
         BDRV_O_PROTOCOL);
 
-    /* Must open the image in writeback mode as long as no BlockBackend is
-     * attached. The right mode can be set as the final step after changing the
-     * medium. */
-    writethrough = !(bdrv_flags & BDRV_O_CACHE_WB);
-    bdrv_flags |= BDRV_O_CACHE_WB;
-
     if (!has_read_only) {
         read_only = BLOCKDEV_CHANGE_READ_ONLY_MODE_RETAIN;
     }
@@ -2611,8 +2596,6 @@ void qmp_blockdev_change_medium(const char *device, const char *filename,
         goto fail;
     }
 
-    bdrv_set_enable_write_cache(medium_bs, !writethrough);
-
     qmp_blockdev_close_tray(device, errp);
 
 fail:
@@ -3238,7 +3221,7 @@ static void do_drive_backup(const char *device, const char *target,
         goto out;
     }
 
-    flags = bs->open_flags | BDRV_O_CACHE_WB | BDRV_O_RDWR;
+    flags = bs->open_flags | BDRV_O_RDWR;
 
     /* See if we have a backing HD we can use to create our new image
      * on top of. */
@@ -3533,7 +3516,7 @@ void qmp_drive_mirror(const char *device, const char *target,
         format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
     }
 
-    flags = bs->open_flags | BDRV_O_CACHE_WB | BDRV_O_RDWR;
+    flags = bs->open_flags | BDRV_O_RDWR;
     source = backing_bs(bs);
     if (!source && sync == MIRROR_SYNC_MODE_TOP) {
         sync = MIRROR_SYNC_MODE_FULL;