[PATCH v4 4/5] block: remember the flags a reopen starts from

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

bdrv_reopen_commit() updates bs->open_flags, so by the time
.bdrv_reopen_commit_post() runs a driver can no longer tell whether
the node has just become writable or was writable all along. Only the
transition is worth reacting to.

Record the flags while the queue is built, next to the other pre-reopen
state BDRVReopenState already keeps, and let a driver ask about them the
way it asks about the node itself. The predicate which
bdrv_is_writable_after_reopen() spells out gets a name for that, and
stays private to block.c.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Hanna Reitz <hreitz@redhat.com>
CC: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Cc: qemu-stable@nongnu.org
---
 block.c                          | 17 ++++++++++++++---
 include/block/block-common.h     |  1 +
 include/block/block_int-common.h |  2 ++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index b29202c8d5..6280a13610 100644
--- a/block.c
+++ b/block.c
@@ -2193,14 +2193,18 @@ static int bdrv_reopen_get_flags(BlockReopenQueue *q, BlockDriverState *bs)
     return bs->open_flags;
 }
 
+/* An inactive node may not be written to, even though it is not read-only */
+static bool bdrv_flags_writable(int flags)
+{
+    return (flags & (BDRV_O_RDWR | BDRV_O_INACTIVE)) == BDRV_O_RDWR;
+}
+
 /* Returns whether the image file can be written to after the reopen queue @q
  * has been successfully applied, or right now if @q is NULL. */
 static bool bdrv_is_writable_after_reopen(BlockDriverState *bs,
                                           BlockReopenQueue *q)
 {
-    int flags = bdrv_reopen_get_flags(q, bs);
-
-    return (flags & (BDRV_O_RDWR | BDRV_O_INACTIVE)) == BDRV_O_RDWR;
+    return bdrv_flags_writable(bdrv_reopen_get_flags(q, bs));
 }
 
 /*
@@ -2214,6 +2218,12 @@ bool bdrv_is_writable(BlockDriverState *bs)
     return bdrv_is_writable_after_reopen(bs, NULL);
 }
 
+bool bdrv_reopen_was_writable(const BDRVReopenState *state)
+{
+    GLOBAL_STATE_CODE();
+    return bdrv_flags_writable(state->old_flags);
+}
+
 static char *bdrv_child_user_desc(BdrvChild *c)
 {
     GLOBAL_STATE_CODE();
@@ -4473,6 +4483,7 @@ bdrv_reopen_queue_child(BlockReopenQueue *bs_queue, BlockDriverState *bs,
     bs_entry->state.options = options;
     bs_entry->state.explicit_options = explicit_options;
     bs_entry->state.flags = flags;
+    bs_entry->state.old_flags = bs->open_flags;
 
     /*
      * If keep_old_opts is false then it means that unspecified
diff --git a/include/block/block-common.h b/include/block/block-common.h
index 895ea17541..eb2dd8aff1 100644
--- a/include/block/block-common.h
+++ b/include/block/block-common.h
@@ -358,6 +358,7 @@ typedef QTAILQ_HEAD(BlockReopenQueue, BlockReopenQueueEntry) BlockReopenQueue;
 typedef struct BDRVReopenState {
     BlockDriverState *bs;
     int flags;
+    int old_flags; /* bs->open_flags is updated on commit */
     BlockdevDetectZeroesOptions detect_zeroes;
     bool backing_missing;
     BlockDriverState *old_backing_bs; /* keep pointer for permissions update */
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 035e54d434..4ea1a78494 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -1346,6 +1346,8 @@ char *create_tmp_file(Error **errp);
 void bdrv_parse_filename_strip_prefix(const char *filename, const char *prefix,
                                       QDict *options);
 
+bool bdrv_reopen_was_writable(const BDRVReopenState *state);
+
 
 int bdrv_check_qiov_request(int64_t offset, int64_t bytes,
                             QEMUIOVector *qiov, size_t qiov_offset,
-- 
2.53.0