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 int pager_open(bool jump_to_end) {
  48         int fd[2];
  49         const char *pager;
  50         pid_t parent_pid;
  51         int r;
  52
  53         if (pager_pid > 0)
  54                 return 1;
  55
  56         if ((pager = getenv("SYSTEMD_PAGER")) || (pager = getenv("PAGER")))
  57                 if (!*pager || streq(pager, "cat"))
  58                         return 0;
  59
  60         if (!on_tty())
  61                 return 0;
  62
  63         /* Determine and cache number of columns before we spawn the
  64          * pager so that we get the value from the actual tty */
  65         columns();
  66
  67         if (pipe(fd) < 0) {
  68                 log_error("Failed to create pager pipe: %m");
  69                 return -errno;
  70         }
  71
  72         parent_pid = getpid();
  73
  74         pager_pid = fork();
  75         if (pager_pid < 0) {
  76                 r = -errno;
  77                 log_error("Failed to fork pager: %m");
  78                 close_pipe(fd);
  79                 return r;
  80         }
  81
  82         /* In the child start the pager */
  83         if (pager_pid == 0) {
  84
  85                 dup2(fd[0], STDIN_FILENO);
  86                 close_pipe(fd);
  87
  88                 if (jump_to_end)
  89                         setenv("LESS", "FRSXMK+G", 1);
  90                 else
  91                         setenv("LESS", "FRSXMK", 1);
  92
  93                 /* Make sure the pager goes away when the parent dies */
  94                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
  95                         _exit(EXIT_FAILURE);
  96
  97                 /* Check whether our parent died before we were able
  98                  * to set the death signal */
  99                 if (getppid() != parent_pid)
 100                         _exit(EXIT_SUCCESS);
 101
 102                 if (pager) {
 103                         execlp(pager, pager, NULL);
 104                         execl("/bin/sh", "sh", "-c", pager, NULL);
 105                 }
 106
 107                 /* Debian's alternatives command for pagers is
 108                  * called 'pager'. Note that we do not call
 109                  * sensible-pagers here, since that is just a
 110                  * shell script that implements a logic that
 111                  * is similar to this one anyway, but is
 112                  * Debian-specific. */
 113                 execlp("pager", "pager", NULL);
 114
 115                 execlp("less", "less", NULL);
 116                 execlp("more", "more", NULL);
 117
 118                 pager_fallback();
 119                 /* not reached */
 120         }
 121
 122         /* Return in the parent */
 123         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 124                 log_error("Failed to duplicate pager pipe: %m");
 125                 return -errno;
 126         }
 127
 128         close_pipe(fd);
 129         return 1;
 130 }
 131
 132 void pager_close(void) {
 133
 134         if (pager_pid <= 0)
 135                 return;
 136
 137         /* Inform pager that we are done */
 138         fclose(stdout);
 139         kill(pager_pid, SIGCONT);
 140         wait_for_terminate(pager_pid, NULL);
 141         pager_pid = 0;
 142 }
 143
 144 bool pager_have(void) {
 145         return pager_pid > 0;
 146 }