Re: [opensuse-kernel] question on tcsetattr

On Thursday, May 26, 2011 09:09:54 PM Ismail Doenmez wrote:

Hi;

Am Thu 26 May 2011 08:53:01 PM CEST schrieb Andreas Jaeger :

...

we have in glibc a patch that reverts this commit: 2003-02-20 Ulrich Drepper

* sysdeps/unix/sysv/linux/tcsetattr.c (tcsetattr): Remove obsolete patch to check for system call errors.

I don't have a comment why the patch is needed. Both Fedora and us have the patch in their current glibc versions.

Can any of you comment on whether we still need this with recent (2.6.32 or newer) kernels or not?

Andreas

Index: sysdeps/unix/sysv/linux/tcsetattr.c =================================================================== --- sysdeps/unix/sysv/linux/tcsetattr.c.orig +++ sysdeps/unix/sysv/linux/tcsetattr.c @@ -49,6 +49,7 @@ tcsetattr (fd, optional_actions, termios

{

struct __kernel_termios k_termios; unsigned long int cmd;

+ int retval;

switch (optional_actions)

{

@@ -80,6 +81,35 @@ tcsetattr (fd, optional_actions, termios

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;

Looks like someone else wondered the same in 2003 [0] , Roland[1] and Ulrich [2] agrees that the patch is unneeded and possibly wrong.

I wonder why it's still enabled in our and Fedora's tree then - without a comment in the changelog ;-( Ok, disabled now and see what breaks ;) thanks, Andreas

Regards, ismail - who is lurking in the -kernel list

[0] http://sources.redhat.com/ml/libc-alpha/2003-02/msg00117.html [1] http://sources.redhat.com/ml/libc-alpha/2003-02/msg00130.html [2] http://sources.redhat.com/ml/libc-alpha/2003-02/msg00161.html

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