src/shared/pager.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2010 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
  10   the Free Software Foundation; either version 2.1 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   Lesser General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <sys/types.h>
  23 #include <fcntl.h>
  24 #include <stdlib.h>
  25 #include <unistd.h>
  26 #include <string.h>
  27 #include <sys/prctl.h>
  28
  29 #include "pager.h"
  30 #include "util.h"
  31 #include "macro.h"
  32
  33 static pid_t pager_pid = 0;
  34
  35 _noreturn_ static void pager_fallback(void) {
  36         ssize_t n;
  37         do {
  38                 n = splice(STDIN_FILENO, NULL, STDOUT_FILENO, NULL, 64*1024, 0);
  39         } while (n > 0);
  40         if (n < 0) {
  41                 log_error("Internal pager failed: %m");
  42                 _exit(EXIT_FAILURE);
  43         }
  44         _exit(EXIT_SUCCESS);
  45 }
  46
  47 bool pager_open(void) {
  48         int fd[2];
  49         const char *pager;
  50         pid_t parent_pid;
  51
  52         if (pager_pid > 0)
  53                 return false;
  54
  55         if ((pager = getenv("SYSTEMD_PAGER")) || (pager = getenv("PAGER")))
  56                 if (!*pager || streq(pager, "cat"))
  57                         return false;
  58
  59         if (isatty(STDOUT_FILENO) <= 0)
  60                 return false;
  61
  62         /* Determine and cache number of columns before we spawn the
  63          * pager so that we get the value from the actual tty */
  64         columns();
  65
  66         if (pipe(fd) < 0) {
  67                 log_error("Failed to create pager pipe: %m");
  68                 return false;
  69         }
  70
  71         parent_pid = getpid();
  72
  73         pager_pid = fork();
  74         if (pager_pid < 0) {
  75                 log_error("Failed to fork pager: %m");
  76                 close_pipe(fd);
  77                 return false;
  78         }
  79
  80         /* In the child start the pager */
  81         if (pager_pid == 0) {
  82
  83                 dup2(fd[0], STDIN_FILENO);
  84                 close_pipe(fd);
  85
  86                 setenv("LESS", "FRSX", 0);
  87
  88                 /* Make sure the pager goes away when the parent dies */
  89                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
  90                         _exit(EXIT_FAILURE);
  91
  92                 /* Check whether our parent died before we were able
  93                  * to set the death signal */
  94                 if (getppid() != parent_pid)
  95                         _exit(EXIT_SUCCESS);
  96
  97                 if (pager) {
  98                         execlp(pager, pager, NULL);
  99                         execl("/bin/sh", "sh", "-c", pager, NULL);
 100                 }
 101
 102                 /* Debian's alternatives command for pagers is
 103                  * called 'pager'. Note that we do not call
 104                  * sensible-pagers here, since that is just a
 105                  * shell script that implements a logic that
 106                  * is similar to this one anyway, but is
 107                  * Debian-specific. */
 108                 execlp("pager", "pager", NULL);
 109
 110                 execlp("less", "less", NULL);
 111                 execlp("more", "more", NULL);
 112
 113                 pager_fallback();
 114                 /* not reached */
 115         }
 116
 117         /* Return in the parent */
 118         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 119                 log_error("Failed to duplicate pager pipe: %m");
 120                 return false;
 121         }
 122
 123         close_pipe(fd);
 124         return true;
 125 }
 126
 127 void pager_close(void) {
 128
 129         if (pager_pid <= 0)
 130                 return;
 131
 132         /* Inform pager that we are done */
 133         fclose(stdout);
 134         kill(pager_pid, SIGCONT);
 135         wait_for_terminate(pager_pid, NULL);
 136         pager_pid = 0;
 137 }