Re: [Qemu-devel] [PATCH v2] block/cow.c : return real error code in cow.c

[Kevin Wolf <kwolf@redhat.com>]

Am 09.12.2011 08:58, schrieb Li Zhi Hui:
> v2: modify some errors
> 
> Signed-off-by: Li Zhi Hui <zhihuili@linux.vnet.ibm.com>
> ---
>  block/cow.c |   31 ++++++++++++++++++-------------
>  1 files changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/block/cow.c b/block/cow.c
> index 3c52735..51ca681 100644
> --- a/block/cow.c
> +++ b/block/cow.c
> @@ -64,15 +64,17 @@ static int cow_open(BlockDriverState *bs, int flags)
>      struct cow_header_v2 cow_header;
>      int bitmap_size;
>      int64_t size;
> +    int ret;
>  
>      /* see if it is a cow image */
> -    if (bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header)) !=
> -            sizeof(cow_header)) {
> +    ret = bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header));
> +    if (ret < 0) {
>          goto fail;
>      }
>  
>      if (be32_to_cpu(cow_header.magic) != COW_MAGIC ||
>          be32_to_cpu(cow_header.version) != COW_VERSION) {
> +        ret = -1;

ret is interpreted as -errno by the caller, so usually on Linux systems
you'll get a -EPERM (Operation not permitted) error message, which
doesn't describe the error very well.

I think a better return value for a wrong magic would be -EINVAL. For a
wrong version have a look at the qcow2 code (qerror_report and -ENOTSUP).

Kevin