block: Support BDRV_REQ_WRITE_UNCHANGED in filters

Update the rest of the filter drivers to support
BDRV_REQ_WRITE_UNCHANGED.  They already forward write request flags to
their children, so we just have to announce support for it.

This patch does not cover the replication driver because that currently
does not support flags at all, and because it just grabs the WRITE
permission for its children when it can, so we should be fine just
submitting the incoming WRITE_UNCHANGED requests as normal writes.

It also does not cover format drivers for similar reasons.  They all use
bdrv_format_default_perms() as their .bdrv_child_perm() implementation
so they just always grab the WRITE permission for their file children
whenever possible.  In addition, it often would be difficult to
ascertain whether incoming unchanging writes end up as unchanging writes
in their files.  So we just leave them as normal potentially changing
writes.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-7-mreitz@redhat.com
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

7 files changed, 28 insertions, 14 deletions

diff --git a/block/blkdebug.c b/block/blkdebug.c
index 053372c..526af2a 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -398,10 +398,11 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
         goto out;
     }
 
-    bs->supported_write_flags = BDRV_REQ_FUA &
-        bs->file->bs->supported_write_flags;
-    bs->supported_zero_flags = (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
-        bs->file->bs->supported_zero_flags;
+    bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
+        (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
+    bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
+        ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+            bs->file->bs->supported_zero_flags);
     ret = -EINVAL;
 
     /* Set alignment overrides */
diff --git a/block/blkreplay.c b/block/blkreplay.c
index fe5a9b4..b016dbe 100755
--- a/block/blkreplay.c
+++ b/block/blkreplay.c
@@ -35,6 +35,9 @@ static int blkreplay_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED;
+    bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED;
+
     ret = 0;
 fail:
     return ret;
diff --git a/block/blkverify.c b/block/blkverify.c
index 754cc9e..da97ee5 100644
--- a/block/blkverify.c
+++ b/block/blkverify.c
@@ -141,6 +141,9 @@ static int blkverify_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED;
+    bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED;
+
     ret = 0;
 fail:
     qemu_opts_del(opts);
diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index 823ec75..6a97208 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -33,11 +33,13 @@ static int cor_open(BlockDriverState *bs, QDict *options, int flags,
         return -EINVAL;
     }
 
-    bs->supported_write_flags = BDRV_REQ_FUA &
-                                    bs->file->bs->supported_write_flags;
+    bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
+                                (BDRV_REQ_FUA &
+                                    bs->file->bs->supported_write_flags);
 
-    bs->supported_zero_flags = (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
-                                    bs->file->bs->supported_zero_flags;
+    bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
+                               ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+                                    bs->file->bs->supported_zero_flags);
 
     return 0;
 }
diff --git a/block/mirror.c b/block/mirror.c
index 6aa38db..a4197bb 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1134,6 +1134,8 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
         mirror_top_bs->implicit = true;
     }
     mirror_top_bs->total_sectors = bs->total_sectors;
+    mirror_top_bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED;
+    mirror_top_bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED;
     bdrv_set_aio_context(mirror_top_bs, bdrv_get_aio_context(bs));
 
     /* bdrv_append takes ownership of the mirror_top_bs reference, need to keep
diff --git a/block/raw-format.c b/block/raw-format.c
index a378547..fe33693 100644
--- a/block/raw-format.c
+++ b/block/raw-format.c
@@ -415,10 +415,11 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     bs->sg = bs->file->bs->sg;
-    bs->supported_write_flags = BDRV_REQ_FUA &
-        bs->file->bs->supported_write_flags;
-    bs->supported_zero_flags = (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
-        bs->file->bs->supported_zero_flags;
+    bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
+        (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
+    bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
+        ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+            bs->file->bs->supported_zero_flags);
 
     if (bs->probed && !bdrv_is_read_only(bs)) {
         fprintf(stderr,
diff --git a/block/throttle.c b/block/throttle.c
index 95ed06a..e298827 100644
--- a/block/throttle.c
+++ b/block/throttle.c
@@ -81,8 +81,10 @@ static int throttle_open(BlockDriverState *bs, QDict *options,
     if (!bs->file) {
         return -EINVAL;
     }
-    bs->supported_write_flags = bs->file->bs->supported_write_flags;
-    bs->supported_zero_flags = bs->file->bs->supported_zero_flags;
+    bs->supported_write_flags = bs->file->bs->supported_write_flags |
+                                BDRV_REQ_WRITE_UNCHANGED;
+    bs->supported_zero_flags = bs->file->bs->supported_zero_flags |
+                               BDRV_REQ_WRITE_UNCHANGED;
 
     return throttle_configure_tgm(bs, tgm, options, errp);
 }