qemu-io: Drop write permissions before read-only reopen

qemu-io provides a 'reopen' command that allows switching from writable
to read-only access. We need to make sure that we don't try to keep
write permissions to a BlockBackend that becomes read-only, otherwise
things are going to fail.

This requires a bdrv_drain() call because otherwise in-flight AIO
write requests could issue new internal requests while the permission
has already gone away, which would cause assertion failures. Draining
the queue doesn't break AIO requests in any new way, bdrv_reopen() would
drain it anyway only a few lines later.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>

diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 2811a890994163054b4b5c3488ce0fc7639ea3e9..3727fb43f35d42caf7e3f2dd14da436fcd315626 100644 (file)
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -2010,6 +2010,18 @@ static int reopen_f(BlockBackend *blk, int argc, char **argv)
         return 0;
     }
 
+    if (!(flags & BDRV_O_RDWR)) {
+        uint64_t orig_perm, orig_shared_perm;
+
+        bdrv_drain(bs);
+
+        blk_get_perm(blk, &orig_perm, &orig_shared_perm);
+        blk_set_perm(blk,
+                     orig_perm & ~(BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED),
+                     orig_shared_perm,
+                     &error_abort);
+    }
+
     qopts = qemu_opts_find(&reopen_opts, NULL);
     opts = qopts ? qemu_opts_to_qdict(qopts, NULL) : NULL;
     qemu_opts_reset(&reopen_opts);

diff --git a/tests/qemu-iotests/187.out b/tests/qemu-iotests/187.out
index 68fb944cd5f60460066f387989b01eaa1921019c..30b987f71f8df7ac02bd398bd8707a86eca67eec 100644 (file)
--- a/tests/qemu-iotests/187.out
+++ b/tests/qemu-iotests/187.out
@@ -12,7 +12,7 @@ Start from read-write
 
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-write failed: Operation not permitted
+Block node is read-only
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 *** done