getgrgid and errno

getgrgid and errno

[Julien Ramseier]

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Hello,

I’m encountering a strange problem with getgrgid.

Calling this function with a non-existent group sets errno to ENOENT instead of 0.
This small test program below prints getgrgid: No such file or directory.

#include <sys/types.h>
#include <grp.h>
#include <stddef.h>
#include <errno.h>

int main(void) {
	errno = 0;
	struct group *g = getgrgid(1234);
	perror("getgrgid");
}

However, when stepping through __getgr_a with gdb, errno seems to be correctly set to 0:

167		if (rv) errno = rv;
(gdb)
168		return rv;
(gdb) p rv
$6 = 0

So I really don’t know what’s going on…Am I missing something?

-
Julien

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Re: getgrgid and errno

[Alex]

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The code which you show says "if (rv) errno = rv". The debugger shows that
rv is 0. So the condition is false and errno is not set.

It must have been set to ENOENT somewhere above that -- as you single-step
through the code, keep printing errno on each line to find out where.

On Tue, Jun 9, 2015 at 2:59 PM, Julien Ramseier <j.ramseier@gmail.com>
wrote:

> Hello,
>
> I’m encountering a strange problem with getgrgid.
>
> Calling this function with a non-existent group sets errno to ENOENT
> instead of 0.
> This small test program below prints getgrgid: No such file or directory.
>
> #include <sys/types.h>
> #include <grp.h>
> #include <stddef.h>
> #include <errno.h>
>
> int main(void) {
> errno = 0;
> struct group *g = getgrgid(1234);
> perror("getgrgid");
> }
>
> However, when stepping through __getgr_a with gdb, errno seems to be
> correctly set to 0:
>
> 167 if (rv) errno = rv;
> (gdb)
> 168 return rv;
> (gdb) p rv
> $6 = 0
>
> So I really don’t know what’s going on…Am I missing something?
>
> -
> Julien
>

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Re: getgrgid and errno

[Julien Ramseier]

> Le 9 juin 2015 à 21:17, Alex <alexinbeijing@gmail.com> a écrit :
> 
> The code which you show says "if (rv) errno = rv". The debugger shows that rv is 0. So the condition is false and errno is not set.
> 
> It must have been set to ENOENT somewhere above that -- as you single-step through the code, keep printing errno on each line to find out where.

Thanks. I don’t know how I missed that.

errno is set to ENOENT by __nscd_query, since no nscd daemon is running and /var/run/nscd/socket does not exist.
So getgrgid always sets errno when the group doesn’t exist and no nscd daemon is available.
Is that expected?

Julien

Re: getgrgid and errno

[Rich Felker]

On Tue, Jun 09, 2015 at 09:46:50PM +0200, Julien Ramseier wrote:
> 
> > Le 9 juin 2015 à 21:17, Alex <alexinbeijing@gmail.com> a écrit :
> > 
> > The code which you show says "if (rv) errno = rv". The debugger shows that rv is 0. So the condition is false and errno is not set.
> > 
> > It must have been set to ENOENT somewhere above that -- as you single-step through the code, keep printing errno on each line to find out where.
> 
> Thanks. I don’t know how I missed that.
> 
> errno is set to ENOENT by __nscd_query, since no nscd daemon is running and /var/run/nscd/socket does not exist.
> So getgrgid always sets errno when the group doesn’t exist and no nscd daemon is available.
> Is that expected?

No, it's a bug/oversight. There should be a fix in git master soon
(and it should safely apply to recent releases if you prefer).

Rich

Re: getgrgid and errno

[Rich Felker]

On Tue, Jun 09, 2015 at 03:52:52PM -0400, Rich Felker wrote:
> On Tue, Jun 09, 2015 at 09:46:50PM +0200, Julien Ramseier wrote:
> > 
> > > Le 9 juin 2015 à 21:17, Alex <alexinbeijing@gmail.com> a écrit :
> > > 
> > > The code which you show says "if (rv) errno = rv". The debugger shows that rv is 0. So the condition is false and errno is not set.
> > > 
> > > It must have been set to ENOENT somewhere above that -- as you single-step through the code, keep printing errno on each line to find out where.
> > 
> > Thanks. I don’t know how I missed that.
> > 
> > errno is set to ENOENT by __nscd_query, since no nscd daemon is running and /var/run/nscd/socket does not exist.
> > So getgrgid always sets errno when the group doesn’t exist and no nscd daemon is available.
> > Is that expected?
> 
> No, it's a bug/oversight. There should be a fix in git master soon
> (and it should safely apply to recent releases if you prefer).

Fixed in commit bd1eaceaa3975bd2a2a34e211cff896affaecadf.

Rich