[Bug libc/11538] New: invalid use of errno after calling ttyname_r

["bruno at clisp dot org" <sourceware-bugzilla at sourceware dot org>]

ttyname_r is specified in POSIX
<http://www.opengroup.org/onlinepubs/9699919799/functions/ttyname.html>.
The return value is specified like this:
"If successful, the ttyname_r() function shall return zero.
 Otherwise, an error number shall be returned to indicate the error."

This means, ttyname_r should return the error number. Whether it
additionally stores it in errno, is not specified. And indeed,
the two implementations in glibc/sysdeps/posix/ttyname_r.c and
glibc/sysdeps/unix/sysv/linux/ttyname_r.c can fail, returning
ENOTTY, without setting errno to ENOTTY. (Look at the end of the
function getttyname_r: If it cannot find the tty, it sets errno to
its previous value ('save') and returns ENOTTY. When all calls to
getttyname_r end like this, __ttyname_r returns ENOTTY without
assigning errno.)

Therefore, callers of ttyname_r should not use the value of errno
after the call failed, but instead use the return value from ttyname_r.

Find attached a fix.

-- 
           Summary: invalid use of errno after calling ttyname_r
           Product: glibc
           Version: 2.11
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: bruno at clisp dot org
                CC: glibc-bugs at sources dot redhat dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://sourceware.org/bugzilla/show_bug.cgi?id=11538

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