[sheepdog] [PATCH 2/2] sheepdog: improve error handling for a case of failed lock

[Hitoshi Mitake]

Recently, sheepdog revived its VDI locking functionality. This patch
updates sheepdog driver of QEMU for this feature:

1. Improve error message when QEMU fails to acquire lock of
VDI. Current sheepdog driver prints an error message "VDI isn't
locked" when it fails to acquire lock. It is a little bit confusing
because the mesage says VDI isn't locked but it is actually locked by
other VM. This patch modifies this confusing message.

2. Change error code for a case of failed locking. -EBUSY is a
suitable one.

Reported-by: Valerio Pachera <sirio81 at gmail.com>
Cc: Kevin Wolf <kwolf at redhat.com>
Cc: Stefan Hajnoczi <stefanha at redhat.com>
Cc: Liu Yuan <namei.unix at gmail.com>
Cc: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
---
 block/sheepdog.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/sheepdog.c b/block/sheepdog.c
index 36f76f0..0b3f86d 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -1112,9 +1112,13 @@ static int find_vdi_name(BDRVSheepdogState *s, const char *filename,
 
     if (rsp->result != SD_RES_SUCCESS) {
         error_setg(errp, "cannot get vdi info, %s, %s %" PRIu32 " %s",
+                   rsp->result == SD_RES_VDI_NOT_LOCKED ?
+                   "VDI is already locked by other VM" :
                    sd_strerror(rsp->result), filename, snapid, tag);
         if (rsp->result == SD_RES_NO_VDI) {
             ret = -ENOENT;
+        } else if (rsp->result == SD_RES_VDI_NOT_LOCKED) {
+            ret = -EBUSY;
         } else {
             ret = -EIO;
         }
-- 
1.8.3.2