[Qemu-devel] [PATCH 1/2] qemu-img: Report bdrv_block_status failures

[Eric Blake]

If bdrv_block_status_above() fails, we are aborting the convert
process but failing to print an error message.  Broken in commit
690c7301 (v2.4) when rewriting convert's logic.

Discovered when teaching nbdkit to support NBD_CMD_BLOCK_STATUS, and
accidentally violating the protocol by returning more than one extent
in spite of qemu asking for NBD_CMD_FLAG_REQ_ONE.  The qemu NBD code
should probably handle the server's non-compliance more gracefully
than failing with EINVAL, but qemu-img shouldn't be silently
squelching any block status failures. It doesn't help that qemu 3.1
masks the qemu-img bug with extra noise that the nbd code is dumping
to stderr (that noise was cleaned up in d8b4bad8).

Reported-by: Richard W.M. Jones <address@hidden>
Signed-off-by: Eric Blake <address@hidden>
---
 qemu-img.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/qemu-img.c b/qemu-img.c
index 5fac8407428..a67c28e9ae5 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1630,6 +1630,8 @@ static int convert_iteration_sectors(ImgConvertState *s, 
int64_t sector_num)
                                           count, &count, NULL, NULL);
         }
         if (ret < 0) {
+            error_report("Could not read sector %" PRId64 " metadata: %s",
+                         sector_num, strerror(-ret));
             return ret;
         }
         n = DIV_ROUND_UP(count, BDRV_SECTOR_SIZE);
-- 
2.20.1