Re: [Qemu-devel] [PATCH] hw/9pfs: Fix errno value for xattr functions

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

"Daniel P. Berrange" <berrange@redhat.com> writes:

> From: "Daniel P. Berrange" <berrange@redhat.com>
>
> If there is no operation driver for the xattr type the
> functions return '-1' and set errno to '-EOPNOTSUPP'.
> When the calling code sets 'ret = -errno' this turns
> into a large positive number.
>
> In Linux 3.11, the kernel has switched to using 9p
> version 9p2000.L, instead of 9p2000.u, which enables
> support for xattr operations. This on its own is harmless,
> but for another change which makes it request the xattr
> with a name 'security.capability'.
>
> The result is that the guest sees a succesful return
> of 95 bytes of data, instead of a failure with errno
> set to 95. Since the kernel expects a maximum of 20
> bytes for an xattr return this gets translated to the
> unexpected errno ERANGE.
>
> This all means that when running a binary off a 9p fs
> in 3.11 kernels you get a fun result of:
>
>   # ./date
>   sh: ./date: Numerical result out of range
>
> The only workaround is to pass 'version=9p2000.u' when
> mounting the 9p fs in the guest, to disable all use of
> xattrs.
>
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>


Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> ---
>  hw/9pfs/virtio-9p-xattr.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/hw/9pfs/virtio-9p-xattr.c b/hw/9pfs/virtio-9p-xattr.c
> index 90ae565..3fae557 100644
> --- a/hw/9pfs/virtio-9p-xattr.c
> +++ b/hw/9pfs/virtio-9p-xattr.c
> @@ -36,7 +36,7 @@ ssize_t v9fs_get_xattr(FsContext *ctx, const char *path,
>      if (xops) {
>          return xops->getxattr(ctx, path, name, value, size);
>      }
> -    errno = -EOPNOTSUPP;
> +    errno = EOPNOTSUPP;
>      return -1;
>  }
>
> @@ -123,7 +123,7 @@ int v9fs_set_xattr(FsContext *ctx, const char *path, const char *name,
>      if (xops) {
>          return xops->setxattr(ctx, path, name, value, size, flags);
>      }
> -    errno = -EOPNOTSUPP;
> +    errno = EOPNOTSUPP;
>      return -1;
>
>  }
> @@ -135,7 +135,7 @@ int v9fs_remove_xattr(FsContext *ctx,
>      if (xops) {
>          return xops->removexattr(ctx, path, name);
>      }
> -    errno = -EOPNOTSUPP;
> +    errno = EOPNOTSUPP;
>      return -1;
>
>  }
> -- 
> 1.8.3.1