Re: [PATCH] virtiofsd: Fix side-effect in assert()

[Wainer dos Santos Moschetta]

On 4/9/21 7:06 AM, Greg Kurz wrote:
> It is bad practice to put an expression with a side-effect in
> assert() because the side-effect won't happen if the code is
> compiled with -DNDEBUG.
>
> Use an intermediate variable. Consolidate this in an macro to
> have proper line numbers when the assertion is hit.
>
> virtiofsd: ../../tools/virtiofsd/passthrough_ll.c:2797: lo_getxattr:
>   Assertion `fchdir_res == 0' failed.
> Aborted
>
>    2796          /* fchdir should not fail here */
> =>2797          FCHDIR_NOFAIL(lo->proc_self_fd);
>    2798          ret = getxattr(procname, name, value, size);
>    2799          FCHDIR_NOFAIL(lo->root.fd);
>
> Fixes: bdfd66788349 ("virtiofsd: Fix xattr operations")
> Cc: misono.tomohiro@jp.fujitsu.com
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
>   tools/virtiofsd/passthrough_ll.c | 21 +++++++++++++--------
>   1 file changed, 13 insertions(+), 8 deletions(-)


Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>


> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> index 1553d2ef454f..6592f96f685e 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -2723,6 +2723,11 @@ static int xattr_map_server(const struct lo_data *lo, 
> const char *server_name,
>       return -ENODATA;
>   }
>   
> +#define FCHDIR_NOFAIL(fd) do {                         \
> +        int fchdir_res = fchdir(fd);                   \
> +        assert(fchdir_res == 0);                       \
> +    } while (0)
> +
>   static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name,
>                           size_t size)
>   {
> @@ -2789,9 +2794,9 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, 
> const char *in_name,
>           ret = fgetxattr(fd, name, value, size);
>       } else {
>           /* fchdir should not fail here */
> -        assert(fchdir(lo->proc_self_fd) == 0);
> +        FCHDIR_NOFAIL(lo->proc_self_fd);
>           ret = getxattr(procname, name, value, size);
> -        assert(fchdir(lo->root.fd) == 0);
> +        FCHDIR_NOFAIL(lo->root.fd);
>       }
>   
>       if (ret == -1) {
> @@ -2864,9 +2869,9 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, 
> size_t size)
>           ret = flistxattr(fd, value, size);
>       } else {
>           /* fchdir should not fail here */
> -        assert(fchdir(lo->proc_self_fd) == 0);
> +        FCHDIR_NOFAIL(lo->proc_self_fd);
>           ret = listxattr(procname, value, size);
> -        assert(fchdir(lo->root.fd) == 0);
> +        FCHDIR_NOFAIL(lo->root.fd);
>       }
>   
>       if (ret == -1) {
> @@ -3000,9 +3005,9 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, 
> const char *in_name,
>           ret = fsetxattr(fd, name, value, size, flags);
>       } else {
>           /* fchdir should not fail here */
> -        assert(fchdir(lo->proc_self_fd) == 0);
> +        FCHDIR_NOFAIL(lo->proc_self_fd);
>           ret = setxattr(procname, name, value, size, flags);
> -        assert(fchdir(lo->root.fd) == 0);
> +        FCHDIR_NOFAIL(lo->root.fd);
>       }
>   
>       saverr = ret == -1 ? errno : 0;
> @@ -3066,9 +3071,9 @@ static void lo_removexattr(fuse_req_t req, fuse_ino_t 
> ino, const char *in_name)
>           ret = fremovexattr(fd, name);
>       } else {
>           /* fchdir should not fail here */
> -        assert(fchdir(lo->proc_self_fd) == 0);
> +        FCHDIR_NOFAIL(lo->proc_self_fd);
>           ret = removexattr(procname, name);
> -        assert(fchdir(lo->root.fd) == 0);
> +        FCHDIR_NOFAIL(lo->root.fd);
>       }
>   
>       saverr = ret == -1 ? errno : 0;