PATCH: linux-generic dup2 behaviour

[Linas Vepstas]

Chris, here's another:

man dup2 states that:
   If  oldfd  is a valid file descriptor, and newfd has the same value as
   oldfd, then dup2() does nothing, and returns newfd.

while the linux kernel does this in fs/fcntl.c:
  if (unlikely(oldfd == newfd)) return -EINVAL;

Which I presume is correct for dup3.
Thus, dup2 needs fixing. Note that m4 test suite catches this.


---
 sysdeps/unix/sysv/linux/generic/dup2.c |    2 ++
 1 file changed, 2 insertions(+)

Index: glibc-2.14/sysdeps/unix/sysv/linux/generic/dup2.c
===================================================================
--- glibc-2.14.orig/sysdeps/unix/sysv/linux/generic/dup2.c  2011-09-13
15:39:03.000000000 -0500
+++ glibc-2.14/sysdeps/unix/sysv/linux/generic/dup2.c 2011-09-13
15:40:09.000000000 -0500
@@ -26,6 +26,8 @@
 int
 __dup2 (int fd, int fd2)
 {
+  /* if fd's are equal, preserve documented dup2 response */
+  if (fd == fd2) return fd;
   return INLINE_SYSCALL(dup3, 3, fd, fd2, 0);
 }
 libc_hidden_def (__dup2)