Re: [Virtio-fs] [PATCH v2 1/2] virtiofsd: Save error code early at the failure callsite

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Vivek Goyal (vgoyal@redhat.com) wrote:
> Change error code handling slightly in lo_setattr(). Right now we seem
> to jump to out_err and assume that "errno" is valid and use that to
> send reply.
> 
> But if caller has to do some other operations before jumping to out_err,
> then it does the dance of first saving errno to saverr and the restore
> errno before jumping to out_err. This makes it more confusing.
> 
> I am about to make more changes where caller will have to do some
> work after error before jumping to out_err. I found it easier to
> change the convention a bit. That is caller saves error in "saverr"
> before jumping to out_err. And out_err uses "saverr" to send error
> back and does not rely on "errno" having actual error.
> 
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Yes, that looks OK, so

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

but please can you send a rebased version, Stefan's recent
security fix changes it around the openat.

Dave


> ---
>  tools/virtiofsd/passthrough_ll.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> index ec1008bceb..6407b1a2e1 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -686,6 +686,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
>              res = fchmodat(lo->proc_self_fd, procname, attr->st_mode, 0);
>          }
>          if (res == -1) {
> +            saverr = errno;
>              goto out_err;
>          }
>      }
> @@ -695,6 +696,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
>  
>          res = fchownat(ifd, "", uid, gid, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
>          if (res == -1) {
> +            saverr = errno;
>              goto out_err;
>          }
>      }
> @@ -707,15 +709,15 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
>              sprintf(procname, "%i", ifd);
>              truncfd = openat(lo->proc_self_fd, procname, O_RDWR);
>              if (truncfd < 0) {
> +                saverr = errno;
>                  goto out_err;
>              }
>          }
>  
>          res = ftruncate(truncfd, attr->st_size);
> +        saverr = res == -1 ? errno : 0;
>          if (!fi) {
> -            saverr = errno;
>              close(truncfd);
> -            errno = saverr;
>          }
>          if (res == -1) {
>              goto out_err;
> @@ -748,6 +750,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
>              res = utimensat(lo->proc_self_fd, procname, tv, 0);
>          }
>          if (res == -1) {
> +            saverr = errno;
>              goto out_err;
>          }
>      }
> @@ -756,7 +759,6 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
>      return lo_getattr(req, ino, fi);
>  
>  out_err:
> -    saverr = errno;
>      lo_inode_put(lo, &inode);
>      fuse_reply_err(req, saverr);
>  }
> -- 
> 2.25.4
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK