[Qemu-devel] [PATCH 2/2] qemu-nbd: Improve error reporting

[Ryota Ozaki]

- use err(3) instead of errx(3) if errno is available
  to report why failed
- let fail prior to daemon(3) if opening a nbd file
  is likely to fail after daemonizing to avoid silent
  failure exit
---
 qemu-nbd.c |   16 +++++++++++-----
 1 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/qemu-nbd.c b/qemu-nbd.c
index b89c361..5f10ff0 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -316,7 +316,7 @@ int main(int argc, char **argv)
     if (disconnect) {
         fd = open(argv[optind], O_RDWR);
         if (fd == -1)
-            errx(errno, "Cannot open %s", argv[optind]);
+            err(errno, "Cannot open %s", argv[optind]);
 
         nbd_disconnect(fd);
 
@@ -333,23 +333,29 @@ int main(int argc, char **argv)
     if (bs == NULL)
         return 1;
 
-    if (bdrv_open(bs, argv[optind], flags) < 0)
-        return 1;
+    if ((ret = bdrv_open(bs, argv[optind], flags)) < 0) {
+        errno = -ret;
+        err(errno, "Failed to bdrv_open '%s'", argv[optind]);
+    }
 
     fd_size = bs->total_sectors * 512;
 
     if (partition != -1 &&
         find_partition(bs, partition, &dev_offset, &fd_size))
-        errx(errno, "Could not find partition %d", partition);
+        err(errno, "Could not find partition %d", partition);
 
     if (device) {
         pid_t pid;
         int sock;
 
+        /* want to fail before daemonizing */
+        if (access(device, R_OK|W_OK) == -1)
+            err(errno, "Could not access '%s'", device);
+
         if (!verbose) {
             /* detach client and server */
             if (daemon(0, 0) == -1) {
-                errx(errno, "Failed to daemonize");
+                err(errno, "Failed to daemonize");
             }
         }
 
-- 
1.6.5.2