[v4,16/23] 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.
Update the testsuite for the improved output.

Further simplify the code by hoisting the error code conversion
into the helper function, rather than repeating it at the callers.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v3: new patch
---
 qemu-img.c                 | 19 +++++--------------
 tests/qemu-iotests/074.out |  2 --
 2 files changed, 5 insertions(+), 16 deletions(-)

On 09/13/2017 12:03 PM, Eric Blake wrote:
> If a read error is encountered during 'qemu-img compare', we
> were printing the "Error while reading offset ..." message twice.
> Update the testsuite for the improved output.
> 
> Further simplify the code by hoisting the error code conversion
> into the helper function, rather than repeating it at the callers.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v3: new patch
> ---
>  qemu-img.c                 | 19 +++++--------------
>  tests/qemu-iotests/074.out |  2 --
>  2 files changed, 5 insertions(+), 16 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index dfccebe6bc..3e1e373e8f 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1196,8 +1196,10 @@ 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
> @@ -1218,7 +1220,7 @@ 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) {
> @@ -1473,11 +1475,6 @@ 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;
>              }
>          }
> @@ -1522,12 +1519,6 @@ 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;
>                  }
>              }
> diff --git a/tests/qemu-iotests/074.out b/tests/qemu-iotests/074.out
> index 8fba5aea9c..ede66c3f81 100644
> --- a/tests/qemu-iotests/074.out
> +++ b/tests/qemu-iotests/074.out
> @@ -4,7 +4,6 @@ Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824
>  wrote 512/512 bytes at offset 512
>  512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>  qemu-img: Error while reading offset 0 of blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
> -qemu-img: Error while reading offset 0: Input/output error
>  4
>  Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824
>  Formatting 'TEST_DIR/t.IMGFMT.2', fmt=IMGFMT size=0
> @@ -12,7 +11,6 @@ Formatting 'TEST_DIR/t.IMGFMT.2', fmt=IMGFMT size=0
>  wrote 512/512 bytes at offset 512
>  512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>  qemu-img: Error while reading offset 0 of blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
> -qemu-img: Error while reading offset 0 of blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
>  Warning: Image size mismatch!
>  4
>  Cleanup
> 

Hm, naively I might assume it's best for the caller to report the error
and to leave the function a nicely self-contained helper, but I won't
insist on it.

Reviewed-by: John Snow <jsnow@redhat.com>