block: do not set BDS read_only if copy_on_read enabled

A few block drivers will set the BDS read_only flag from their
.bdrv_open() function.  This means the bs->read_only flag could
be set after we enable copy_on_read, as the BDRV_O_COPY_ON_READ
flag check occurs prior to the call to bdrv->bdrv_open().

This adds an error return to bdrv_set_read_only(), and an error will be
return if we try to set the BDS to read_only while copy_on_read is
enabled.

This patch also changes the behavior of vvfat.  Before, vvfat could
override the drive 'readonly' flag with its own, internal 'rw' flag.

For instance, this -drive parameter would result in a writable image:

"-drive format=vvfat,dir=/tmp/vvfat,rw,if=virtio,readonly=on"

This is not correct.  Now, attempting to use the above -drive parameter
will result in an error (i.e., 'rw' is incompatible with 'readonly=on').

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 0c5b4c1cc2c651471b131f21376dfd5ea24d2196.1491597120.git.jcody@redhat.com

1 files changed, 9 insertions, 1 deletions

diff --git a/block.c b/block.c
index 6f21145689..67ae35a47a 100644
--- a/block.c
+++ b/block.c
@@ -192,9 +192,17 @@ void path_combine(char *dest, int dest_size,
     }
 }
 
-void bdrv_set_read_only(BlockDriverState *bs, bool read_only)
+int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp)
 {
+    /* Do not set read_only if copy_on_read is enabled */
+    if (bs->copy_on_read && read_only) {
+        error_setg(errp, "Can't set node '%s' to r/o with copy-on-read enabled",
+                   bdrv_get_device_or_node_name(bs));
+        return -EINVAL;
+    }
+
     bs->read_only = read_only;
+    return 0;
 }
 
 void bdrv_get_full_backing_filename_from_filename(const char *backed,