[Virtio-fs] [PATCH] virtiofsd: Fix side-effect in assert()
Stefan Weil
sw at weilnetz.de
Fri Apr 9 15:11:13 UTC 2021
Am 09.04.21 um 12:06 schrieb Greg Kurz:
> 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 at jp.fujitsu.com
> Signed-off-by: Greg Kurz <groug at kaod.org>
> ---
> tools/virtiofsd/passthrough_ll.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> 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,
>
I am afraid that this will raise a compiler warning (or error with
-Werror) when NDEBUG is defined because the variable is unused in that
case ([-Wunused-variable]).
I suggest to use different implementations of the macro depending on NDEBUG.
Stefan
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