Re: [Qemu-block] [PATCH v2 1/1] block: improve error handling in raw_open

[Max Reitz]

On 26.07.2016 13:34, Halil Pasic wrote:
> Make raw_open for POSIX more consistent in handling errors by setting
> the error object also when qemu_open fails. The error object was set
> generally set in case of errors, but I guess this case was overlooked.
> Do the same for win32.
> 
> Signed-off-by: Halil Pasic <address@hidden>
> Reviewed-by: Sascha Silbe <address@hidden>
> Tested-by: Marc Hartmayer <address@hidden> (POSIX only)
> 
> ---
> 
> Stumbled upon this (POSIX) while testing VMs with too many SCSI disks in
> respect to my nofile limit. When open hits the nofile limit while trying
> to hotplug yet another SCSI disk via libvirt we end up with no adequate
> error message (one stating too many files). Sadly this patch in not
> sufficient to fix this problem because drive_new (/qemu/blockdev.c)
> handles errors using error_report_err which is documented as not to be
> used in QMP context. Do not have a patch for that, because I'm unsure
> whats the best way to deal with it. My guess right now is to make sure
> we propagate errors at least until reaching code which is called  only
> QMP in context and handle communicating the error to the requester of
> the operation there. Any suggestions or ideas?
> 
> The win32 part was not tested, and the sole reason I touched it is
> to not introduce unnecessary divergence.
> 
> v1 -> v2:
> * fixed win32 by the correct error_setg_*
> * use the original errno consequently
> 
> ---
>  block/raw-posix.c | 1 +
>  block/raw-win32.c | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index c979ac3..786f068 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -485,6 +485,7 @@ static int raw_open_common(BlockDriverState *bs, QDict 
> *options,
>      s->fd = -1;
>      fd = qemu_open(filename, s->open_flags, 0644);
>      if (fd < 0) {
> +        error_setg_errno(errp, errno, "Could not open file");

We don't guarantee that error_setg_errno() does not modify errno. (In
practice it should not, but we don't guarantee that.)

Therefore, the common pattern is to save the errno value before calling
this function, i.e. to put the function call...

>          ret = -errno;

...here.

With that fixed, the patch should be good.

Max

>          if (ret == -EROFS) {
>              ret = -EACCES;
> diff --git a/block/raw-win32.c b/block/raw-win32.c
> index 62edb1a..6f074f4 100644
> --- a/block/raw-win32.c
> +++ b/block/raw-win32.c
> @@ -337,6 +337,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, 
> int flags,
>      if (s->hfile == INVALID_HANDLE_VALUE) {
>          int err = GetLastError();
>  
> +        error_setg_win32(errp, err, "Could not open file");
>          if (err == ERROR_ACCESS_DENIED) {
>              ret = -EACCES;
>          } else {
>

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