[Qemu-devel] [PATCH] block: Save errno before error_setg_errno

[Qemu-devel] [PATCH] block: Save errno before error_setg_errno

[Max Reitz]

error_setg_errno() may overwrite errno; therefore, its value should be
read before calling that function and not afterwards.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 58efb5b..0e96a22 100644
--- a/block.c
+++ b/block.c
@@ -1084,8 +1084,8 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
             snprintf(backing_filename, sizeof(backing_filename),
                      "%s", filename);
         } else if (!realpath(filename, backing_filename)) {
-            error_setg_errno(errp, errno, "Could not resolve path '%s'", filename);
             ret = -errno;
+            error_setg_errno(errp, errno, "Could not resolve path '%s'", filename);
             goto fail;
         }
 
-- 
1.8.4.2

Re: [Qemu-devel] [PATCH] block: Save errno before error_setg_errno

[Eric Blake]

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On 11/05/2013 12:03 PM, Max Reitz wrote:
> error_setg_errno() may overwrite errno; therefore, its value should be
> read before calling that function and not afterwards.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

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

Still, wouldn't it be easier to patch error_setg_errno (and friends) to
guarantee that errno is unchanged on exit compared to its value on
entrance, rather than having to audit for other mistakes like this?

> 
> diff --git a/block.c b/block.c
> index 58efb5b..0e96a22 100644
> --- a/block.c
> +++ b/block.c
> @@ -1084,8 +1084,8 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
>              snprintf(backing_filename, sizeof(backing_filename),
>                       "%s", filename);
>          } else if (!realpath(filename, backing_filename)) {
> -            error_setg_errno(errp, errno, "Could not resolve path '%s'", filename);
>              ret = -errno;
> +            error_setg_errno(errp, errno, "Could not resolve path '%s'", filename);
>              goto fail;
>          }
>  
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH] block: Save errno before error_setg_errno

[Benoît Canet]

Le Tuesday 05 Nov 2013 à 20:03:33 (+0100), Max Reitz a écrit :
> error_setg_errno() may overwrite errno; therefore, its value should be
> read before calling that function and not afterwards.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index 58efb5b..0e96a22 100644
> --- a/block.c
> +++ b/block.c
> @@ -1084,8 +1084,8 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
>              snprintf(backing_filename, sizeof(backing_filename),
>                       "%s", filename);
>          } else if (!realpath(filename, backing_filename)) {
> -            error_setg_errno(errp, errno, "Could not resolve path '%s'", filename);
>              ret = -errno;
> +            error_setg_errno(errp, errno, "Could not resolve path '%s'", filename);
>              goto fail;
>          }
>  
> -- 
> 1.8.4.2
> 

Reviewed-by: Benoit Canet <benoit@irqsave.net>
> 

Re: [Qemu-devel] [PATCH] block: Save errno before error_setg_errno

[Stefan Hajnoczi]

On Tue, Nov 05, 2013 at 08:03:33PM +0100, Max Reitz wrote:
> error_setg_errno() may overwrite errno; therefore, its value should be
> read before calling that function and not afterwards.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

Re: [Qemu-devel] [PATCH] block: Save errno before error_setg_errno

[Stefan Hajnoczi]

On Tue, Nov 05, 2013 at 12:26:41PM -0700, Eric Blake wrote:
> On 11/05/2013 12:03 PM, Max Reitz wrote:
> > error_setg_errno() may overwrite errno; therefore, its value should be
> > read before calling that function and not afterwards.
> > 
> > Signed-off-by: Max Reitz <mreitz@redhat.com>
> > ---
> >  block.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> Still, wouldn't it be easier to patch error_setg_errno (and friends) to
> guarantee that errno is unchanged on exit compared to its value on
> entrance, rather than having to audit for other mistakes like this?

Agreed, that can be done as a separate patch.

Stefan