Short description: Fedora-specific workaround for kernel pty bug.

Author(s): Fedora glibc team <glibc@lists.fedoraproject.org>

Origin: PATCH

Upstream status: not-submitted

This is a Fedora-specific workaround for a kernel bug where calling

ioctl on a pty will silently ignore the invalid c_cflag. The

workaround is to use TCGETS to verify the setting matches. This is

not upstream and needs to either be removed or submitted upstream

after analysis.

Index: b/sysdeps/unix/sysv/linux/tcsetattr.c

===================================================================

--- a/sysdeps/unix/sysv/linux/tcsetattr.c

+++ b/sysdeps/unix/sysv/linux/tcsetattr.c

@@ -45,6 +45,7 @@ __tcsetattr (int fd, int optional_action

 {

   struct __kernel_termios k_termios;

   unsigned long int cmd;

+  int retval;

   switch (optional_actions)

     {

@@ -75,7 +76,36 @@ __tcsetattr (int fd, int optional_action

   memcpy (&k_termios.c_cc[0], &termios_p->c_cc[0],

 	  __KERNEL_NCCS * sizeof (cc_t));

-  return INLINE_SYSCALL (ioctl, 3, fd, cmd, &k_termios);

+  retval = INLINE_SYSCALL (ioctl, 3, fd, cmd, &k_termios);

+

+  if (retval == 0 && cmd == TCSETS)

+    {

+      /* The Linux kernel has a bug which silently ignore the invalid

+        c_cflag on pty. We have to check it here. */

+      int save = errno;

+      retval = INLINE_SYSCALL (ioctl, 3, fd, TCGETS, &k_termios);

+      if (retval)

+       {

+         /* We cannot verify if the setting is ok. We don't return

+            an error (?). */

+         __set_errno (save);

+         retval = 0;

+       }

+      else if ((termios_p->c_cflag & (PARENB | CREAD))

+              != (k_termios.c_cflag & (PARENB | CREAD))

+              || ((termios_p->c_cflag & CSIZE)

+                  && ((termios_p->c_cflag & CSIZE)

+                      != (k_termios.c_cflag & CSIZE))))

+       {

+         /* It looks like the Linux kernel silently changed the

+            PARENB/CREAD/CSIZE bits in c_cflag. Report it as an

+            error. */

+         __set_errno (EINVAL);

+         retval = -1;

+       }

+    }

+

+  return retval;

 }

 weak_alias (__tcsetattr, tcsetattr)

 libc_hidden_def (tcsetattr)