flag parameters: dup2

This patch adds the new dup3 syscall.  It extends the old dup2 syscall by one
parameter which is meant to hold a flag value.  Support for the O_CLOEXEC flag
is added in this patch.

The following test must be adjusted for architectures other than x86 and
x86-64 and in case the syscall numbers changed.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <fcntl.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <sys/syscall.h>

#ifndef __NR_dup3
# ifdef __x86_64__
#  define __NR_dup3 292
# elif defined __i386__
#  define __NR_dup3 330
# else
#  error "need __NR_dup3"
# endif
#endif

int
main (void)
{
  int fd = syscall (__NR_dup3, 1, 4, 0);
  if (fd == -1)
    {
      puts ("dup3(0) failed");
      return 1;
    }
  int coe = fcntl (fd, F_GETFD);
  if (coe == -1)
    {
      puts ("fcntl failed");
      return 1;
    }
  if (coe & FD_CLOEXEC)
    {
      puts ("dup3(0) set close-on-exec flag");
      return 1;
    }
  close (fd);

  fd = syscall (__NR_dup3, 1, 4, O_CLOEXEC);
  if (fd == -1)
    {
      puts ("dup3(O_CLOEXEC) failed");
      return 1;
    }
  coe = fcntl (fd, F_GETFD);
  if (coe == -1)
    {
      puts ("fcntl failed");
      return 1;
    }
  if ((coe & FD_CLOEXEC) == 0)
    {
      puts ("dup3(O_CLOEXEC) set close-on-exec flag");
      return 1;
    }
  close (fd);

  puts ("OK");

  return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 330a7d782591..9679fcbdeaa0 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -125,13 +125,16 @@ static int dupfd(struct file *file, unsigned int start, int cloexec)
         return fd;
 }
 
-asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
+asmlinkage long sys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 {
         int err = -EBADF;
         struct file * file, *tofree;
         struct files_struct * files = current->files;
         struct fdtable *fdt;
 
+        if ((flags & ~O_CLOEXEC) != 0)
+                return -EINVAL;
+
         spin_lock(&files->file_lock);
         if (!(file = fcheck(oldfd)))
                 goto out_unlock;
@@ -163,7 +166,10 @@ asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
 
         rcu_assign_pointer(fdt->fd[newfd], file);
         FD_SET(newfd, fdt->open_fds);
-        FD_CLR(newfd, fdt->close_on_exec);
+        if (flags & O_CLOEXEC)
+                FD_SET(newfd, fdt->close_on_exec);
+        else
+                FD_CLR(newfd, fdt->close_on_exec);
         spin_unlock(&files->file_lock);
 
         if (tofree)
@@ -181,6 +187,11 @@ out_fput:
         goto out;
 }
 
+asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
+{
+        return sys_dup3(oldfd, newfd, 0);
+}
+
 asmlinkage long sys_dup(unsigned int fildes)
 {
         int ret = -EBADF;