Re: Bug#81059: fstat misbehaviour: errno set inappropriately

[Ben Collins <bcollins at debian dot org>]

Seems errno wasn't getting reset if a program called fxstat which tried to
call fstat64 and got ENOSYS. I'm not sure if this is the proper fix, but
I have provided a testcase which shows the problem. Note, the testcase
only works when you compile glibc against LFS capable kernel headers,
and then try to run it on a non-LFS capable kernel. I don't know any
other way around this.

2001-01-01  Ben Collins  <bcollins@debian.org>

	* sysdeps/unix/sysv/linux/i386/fxstat.c: Reset the old errno if
	  the syscall for fstat64 fails with ENOSYS.

-- 
 -----------=======-=-======-=========-----------=====------------=-=------
/  Ben Collins  --  ...on that fantastic voyage...  --  Debian GNU/Linux   \
`  bcollins@debian.org  --  bcollins@openldap.org  --  bcollins@linux.com  '
 `---=========------=======-------------=-=-----=-===-======-------=--=---'
Index: sysdeps/unix/sysv/linux/i386/fxstat.c
===================================================================
RCS file: /cvs/glibc/libc/sysdeps/unix/sysv/linux/i386/fxstat.c,v
retrieving revision 1.7
diff -u -u -r1.7 fxstat.c
--- fxstat.c	2000/08/12 05:02:43	1.7
+++ fxstat.c	2001/01/02 15:56:18
@@ -73,6 +73,7 @@
   if (! __have_no_stat64)
     {
       struct stat64 buf64;
+      int olderror = errno;
 
       result = INLINE_SYSCALL (fstat64, 2, fd, __ptrvalue (&buf64));
 
@@ -81,6 +82,8 @@
 
       if (result != -1 || errno != ENOSYS)
 	return result;
+
+      __set_errno(olderror);
 
       __have_no_stat64 = 1;
     }
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

#define TESTFILE "testfile"

int main(int argc, char *argv[])
{
  struct stat S;
  int fd;

  system("touch " TESTFILE);

  fd = open(TESTFILE, O_RDONLY);

  /* This shouldn't happen, and isn't what we are testing.  */
  if (fstat(fd, &S)) {
    perror(TESTFILE);
    exit(1);
  }

  /* This should also succeed.  */
  errno = 0;
  if (fstat(fd, &S)) {
    perror(TESTFILE);
    exit(1);
  }

  /* Now, here's the real test. This should be 0.  */
  if (errno) {
    perror("Failed");
    exit(1);
  }

  exit(0);
}