[Qemu-devel] [PATCH] block: better error message for read only format name

[Fam Zheng <famz@redhat.com>]

When user tries to use read-only whitelist format in the command line
option, failure message was "'foo' invalid format". It might be invalid
only for writable, but valid for read-only, so it is confusing. Give the
user easier to understand information.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockdev.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index bc7016a..d3500c6 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -487,7 +487,11 @@ static DriveInfo *blockdev_init(QemuOpts *all_opts,
 
         drv = bdrv_find_whitelisted_format(buf, ro);
         if (!drv) {
-            error_report("'%s' invalid format", buf);
+            if (!ro && bdrv_find_whitelisted_format(buf, !ro)) {
+                error_report("'%s' can be only used as read-only device.", buf);
+            } else {
+                error_report("'%s' invalid format", buf);
+            }
             return NULL;
         }
     }
-- 
1.8.3.1