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

[Liu Yuan <namei.unix@gmail.com>]

On Thu, Aug 07, 2014 at 04:28:40PM +0900, Hitoshi Mitake wrote:
> 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@gmail.com>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Liu Yuan <namei.unix@gmail.com>
> Cc: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
> Signed-off-by: Hitoshi Mitake <mitake.hitoshi@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 ?

I'm puzzled by this check.

we use SD_RES_VDI_LOCKED to indicate vid is already locked, no?

> +                   "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;
>          }

It is better to use switch case to handle the result.

Thanks
Yuan