qemu-img: Drop redundant error message in compare

If a read error is encountered during 'qemu-img compare', we
were printing the "Error while reading offset ..." message twice;
this was because our helper function was awkward, printing output
on some but not all paths.  Fix it to consistently report errors
on all paths, so that the callers do not risk a redundant message,
and update the testsuite for the improved output.

Further simplify the code by hoisting the conversion from an error
message to an exit code into the helper function, rather than
repeating that logic at all callers (yes, the helper function is
now less generic, but it's a net win in lines of code).

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 14 deletions

diff --git a/qemu-img.c b/qemu-img.c
index 89f1093d81..53cae6bb66 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1197,8 +1197,10 @@ static int64_t sectors_to_bytes(int64_t sectors)
 /*
  * Check if passed sectors are empty (not allocated or contain only 0 bytes)
  *
- * Returns 0 in case sectors are filled with 0, 1 if sectors contain non-zero
- * data and negative value on error.
+ * Intended for use by 'qemu-img compare': Returns 0 in case sectors are
+ * filled with 0, 1 if sectors contain non-zero data (this is a comparison
+ * failure), and 4 on error (the exit status for read errors), after emitting
+ * an error message.
  *
  * @param blk:  BlockBackend for the image
  * @param sect_num: Number of first sector to check
@@ -1219,7 +1221,7 @@ static int check_empty_sectors(BlockBackend *blk, int64_t sect_num,
     if (ret < 0) {
         error_report("Error while reading offset %" PRId64 " of %s: %s",
                      sectors_to_bytes(sect_num), filename, strerror(-ret));
-        return ret;
+        return 4;
     }
     idx = find_nonzero(buffer, sect_count * BDRV_SECTOR_SIZE);
     if (idx >= 0) {
@@ -1476,11 +1478,6 @@ static int img_compare(int argc, char **argv)
                                           filename2, buf1, quiet);
             }
             if (ret) {
-                if (ret < 0) {
-                    error_report("Error while reading offset %" PRId64 ": %s",
-                                 sectors_to_bytes(sector_num), strerror(-ret));
-                    ret = 4;
-                }
                 goto out;
             }
         }
@@ -1525,12 +1522,6 @@ static int img_compare(int argc, char **argv)
                 ret = check_empty_sectors(blk_over, sector_num, nb_sectors,
                                           filename_over, buf1, quiet);
                 if (ret) {
-                    if (ret < 0) {
-                        error_report("Error while reading offset %" PRId64
-                                     " of %s: %s", sectors_to_bytes(sector_num),
-                                     filename_over, strerror(-ret));
-                        ret = 4;
-                    }
                     goto out;
                 }
             }