libutil/login.c

   1 #include <errno.h>
   2 #include <limits.h>
   3 #include <string.h>
   4 #include <unistd.h>
   5 #include <stdlib.h>
   6 #include "internal/utmp.h"
   7
   8 /* Write the given entry into utmp and wtmp.
   9  * Note: the match in utmp is done against ut_id field,
  10  * which is NOT set by this function - caller must set it.
  11  */
  12 void login(const struct utmp *entry)
  13 {
  14         struct UT copy;
  15         char tty_name[sizeof(copy.ut_line) + 6];
  16         int fd;
  17
  18 // Manpage:
  19 // login() takes the argument ut struct, fills the field ut->ut_type
  20 // (if there is such a field) with the value USER_PROCESS,
  21 // and fills the field ut->ut_pid (if there is such a field)
  22 // with the process ID of the calling process.
  23         copy = *((const struct UT *)(entry));
  24 #if _HAVE_UT_TYPE - 0
  25         copy.ut_type = USER_PROCESS;
  26 #endif
  27 #if _HAVE_UT_PID - 0
  28         copy.ut_pid = getpid();
  29 #endif
  30
  31 // Then it tries to fill the field ut->ut_line. It takes the first of stdin,
  32 // stdout, stderr that is a tty, and stores the corresponding pathname minus
  33 // a possible leading /dev/ into this field, and then writes the struct
  34 // to the utmp file. On the other hand, if no tty name was found,
  35 // this field is filled with "???" and the struct is not written
  36 // to the utmp file.
  37         fd = 0;
  38         while (fd != 3 && ttyname_r(fd, tty_name, sizeof(tty_name)) != 0)
  39                 fd++;
  40         if (fd != 3) {
  41                 if (strncmp(tty_name, "/dev/", 5) == 0)
  42                         strncpy(copy.ut_line, tty_name + 5, sizeof(copy.ut_line)-1);
  43                 else
  44                         strncpy(copy.ut_line, tty_name, sizeof(copy.ut_line)-1);
  45                 copy.ut_line[sizeof(copy.ut_line)-1] = '\0';
  46
  47                 /* utmpname(_PATH_UTMP); - why?
  48                  * this makes it impossible for caller to use other file!
  49                  * Does any standard or historical precedent says this must be done? */
  50                 setutent();
  51                 /* Replaces record with matching ut_id, or appends new one: */
  52                 pututline(&copy);
  53                 endutent();
  54         } else {
  55                 strncpy(copy.ut_line, "???", sizeof(copy.ut_line));
  56         }
  57
  58 // After this, the struct is written to the wtmp file.
  59         updwtmp(_PATH_WTMP, &copy);
  60 }