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glibc  2.9
tcgetsid.c
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00001 /* Copyright (C) 1997, 1999 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003 
00004    The GNU C Library is free software; you can redistribute it and/or
00005    modify it under the terms of the GNU Lesser General Public
00006    License as published by the Free Software Foundation; either
00007    version 2.1 of the License, or (at your option) any later version.
00008 
00009    The GNU C Library is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012    Lesser General Public License for more details.
00013 
00014    You should have received a copy of the GNU Lesser General Public
00015    License along with the GNU C Library; if not, write to the Free
00016    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00017    02111-1307 USA.  */
00018 
00019 #include <errno.h>
00020 #include <termios.h>
00021 #include <sys/ioctl.h>
00022 #include <sys/types.h>
00023 #include <unistd.h>
00024 
00025 /* Return the session ID of FD.  */
00026 pid_t
00027 tcgetsid (fd)
00028      int fd;
00029 {
00030   pid_t pgrp;
00031   pid_t sid;
00032 #ifdef TIOCGSID
00033   static int tiocgsid_does_not_work;
00034 
00035   if (! tiocgsid_does_not_work)
00036     {
00037       int serrno = errno;
00038       int sid;
00039 
00040       if (__ioctl (fd, TIOCGSID, &sid) < 0)
00041        {
00042          if (errno == EINVAL)
00043            {
00044              tiocgsid_does_not_work = 1;
00045              __set_errno (serrno);
00046            }
00047          else
00048            return (pid_t) -1;
00049        }
00050       else
00051        return (pid_t) sid;
00052     }
00053 #endif
00054 
00055   pgrp = tcgetpgrp (fd);
00056   if (pgrp == -1)
00057     return (pid_t) -1;
00058 
00059   sid = getsid (pgrp);
00060   if (sid == -1 && errno == ESRCH)
00061     __set_errno (ENOTTY);
00062 
00063   return sid;
00064 }