Re: [PATCH] src/t_ofd_locks.c: Reset errno to zero

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Aug 15, 2022 at 10:06:59AM +0000, xuyang2018.jy@fujitsu.com wrote:
> 
> 
> on 2022/08/05 23:00, Darrick J. Wong wrote:
> > On Thu, Aug 04, 2022 at 02:18:52PM +0800, Yang Xu wrote:
> >> It seems I met libcap errno bug again when using libcap-2.48-4.el8.x86_64.
> >> But this time, errno is EINVAL if c program link with lcap.
> >> Lastest upstream libcap doesn't have bug and it should be backport bug.
> >>
> >> generic/478 will become not run because of this. To fix this that only
> >> exists on some distributions, reset errno to zero.
> >>
> >> Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
> >> ---
> >>   src/t_ofd_locks.c | 2 ++
> >>   1 file changed, 2 insertions(+)
> >>
> >> diff --git a/src/t_ofd_locks.c b/src/t_ofd_locks.c
> >> index e3b15ddc..e77f2659 100644
> >> --- a/src/t_ofd_locks.c
> >> +++ b/src/t_ofd_locks.c
> >> @@ -187,6 +187,8 @@ int main(int argc, char **argv)
> >>   	struct sembuf sop;
> >>   	int opt, ret, retry;
> >>   
> >> +	//avoid libcap errno bug
> >> +	errno = 0;
> > 
> > What sets errno to EINVAL here?  And what actually causes the program to
> > exit with code 22?
> > 
> > There aren't any library calls prior to this point, right?  Or is this
> > ... libpcap has some initcall that runs quietly in the background before
> > main starts, so we enter main with errno==EINVAL, which then causes ...
> > something else to break?
> Yes,
> 
> #include <stdio.h>
> #include <errno.h>
> int main(int argc, char **argv)
> {
>          printf("errno %d\n", errno);
>          return 0;
> }
> 
> gcc test.c -lcap -o test
> 
> then run test, errno is EINVAL.
> 
> But upstream libcap is ok and it should be a backport bug on libcap 
> distribution version.

Yay for still paying for poor decisions of the 1970s in 2022...

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> 
> Best Regards
> Yang Xu
> > 
> > --D
> > 
> >>   	while((opt = getopt(argc, argv, "sgrwo:l:PRWtFd")) != -1) {
> >>   		switch(opt) {
> >>   		case 's':
> >> -- 
> >> 2.27.0
> >>