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 <fcntl.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include <string.h>
  26 #include <sys/prctl.h>
  27
  28 #include "pager.h"
  29 #include "util.h"
  30 #include "process-util.h"
  31 #include "macro.h"
  32 #include "terminal-util.h"
  33
  34 static pid_t pager_pid = 0;
  35
  36 noreturn static void pager_fallback(void) {
  37         ssize_t n;
  38
  39         do {
  40                 n = splice(STDIN_FILENO, NULL, STDOUT_FILENO, NULL, 64*1024, 0);
  41         } while (n > 0);
  42
  43         if (n < 0) {
  44                 log_error_errno(errno, "Internal pager failed: %m");
  45                 _exit(EXIT_FAILURE);
  46         }
  47
  48         _exit(EXIT_SUCCESS);
  49 }
  50
  51 int pager_open(bool jump_to_end) {
  52         int fd[2];
  53         const char *pager;
  54         pid_t parent_pid;
  55         int r;
  56
  57         if (pager_pid > 0)
  58                 return 1;
  59
  60         if ((pager = getenv("SYSTEMD_PAGER")) || (pager = getenv("PAGER")))
  61                 if (!*pager || streq(pager, "cat"))
  62                         return 0;
  63
  64         if (!on_tty())
  65                 return 0;
  66
  67         /* Determine and cache number of columns before we spawn the
  68          * pager so that we get the value from the actual tty */
  69         columns();
  70
  71         if (pipe(fd) < 0)
  72                 return log_error_errno(errno, "Failed to create pager pipe: %m");
  73
  74         parent_pid = getpid();
  75
  76         pager_pid = fork();
  77         if (pager_pid < 0) {
  78                 r = -errno;
  79                 log_error_errno(errno, "Failed to fork pager: %m");
  80                 safe_close_pair(fd);
  81                 return r;
  82         }
  83
  84         /* In the child start the pager */
  85         if (pager_pid == 0) {
  86                 const char* less_opts;
  87
  88                 dup2(fd[0], STDIN_FILENO);
  89                 safe_close_pair(fd);
  90
  91                 less_opts = getenv("SYSTEMD_LESS");
  92                 if (!less_opts)
  93                         less_opts = "FRSXMK";
  94                 if (jump_to_end)
  95                         less_opts = strjoina(less_opts, " +G");
  96                 setenv("LESS", less_opts, 1);
  97
  98                 /* Make sure the pager goes away when the parent dies */
  99                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
 100                         _exit(EXIT_FAILURE);
 101
 102                 /* Check whether our parent died before we were able
 103                  * to set the death signal */
 104                 if (getppid() != parent_pid)
 105                         _exit(EXIT_SUCCESS);
 106
 107                 if (pager) {
 108                         execlp(pager, pager, NULL);
 109                         execl("/bin/sh", "sh", "-c", pager, NULL);
 110                 }
 111
 112                 /* Debian's alternatives command for pagers is
 113                  * called 'pager'. Note that we do not call
 114                  * sensible-pagers here, since that is just a
 115                  * shell script that implements a logic that
 116                  * is similar to this one anyway, but is
 117                  * Debian-specific. */
 118                 execlp("pager", "pager", NULL);
 119
 120                 execlp("less", "less", NULL);
 121                 execlp("more", "more", NULL);
 122
 123                 pager_fallback();
 124                 /* not reached */
 125         }
 126
 127         /* Return in the parent */
 128         if (dup2(fd[1], STDOUT_FILENO) < 0)
 129                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 130
 131         safe_close_pair(fd);
 132         return 1;
 133 }
 134
 135 void pager_close(void) {
 136
 137         if (pager_pid <= 0)
 138                 return;
 139
 140         /* Inform pager that we are done */
 141         fclose(stdout);
 142         kill(pager_pid, SIGCONT);
 143         (void) wait_for_terminate(pager_pid, NULL);
 144         pager_pid = 0;
 145 }
 146
 147 bool pager_have(void) {
 148         return pager_pid > 0;
 149 }
 150
 151 int show_man_page(const char *desc, bool null_stdio) {
 152         const char *args[4] = { "man", NULL, NULL, NULL };
 153         char *e = NULL;
 154         pid_t pid;
 155         size_t k;
 156         int r;
 157         siginfo_t status;
 158
 159         k = strlen(desc);
 160
 161         if (desc[k-1] == ')')
 162                 e = strrchr(desc, '(');
 163
 164         if (e) {
 165                 char *page = NULL, *section = NULL;
 166
 167                 page = strndupa(desc, e - desc);
 168                 section = strndupa(e + 1, desc + k - e - 2);
 169
 170                 args[1] = section;
 171                 args[2] = page;
 172         } else
 173                 args[1] = desc;
 174
 175         pid = fork();
 176         if (pid < 0)
 177                 return log_error_errno(errno, "Failed to fork: %m");
 178
 179         if (pid == 0) {
 180                 /* Child */
 181                 if (null_stdio) {
 182                         r = make_null_stdio();
 183                         if (r < 0) {
 184                                 log_error_errno(r, "Failed to kill stdio: %m");
 185                                 _exit(EXIT_FAILURE);
 186                         }
 187                 }
 188
 189                 execvp(args[0], (char**) args);
 190                 log_error_errno(errno, "Failed to execute man: %m");
 191                 _exit(EXIT_FAILURE);
 192         }
 193
 194         r = wait_for_terminate(pid, &status);
 195         if (r < 0)
 196                 return r;
 197
 198         log_debug("Exit code %i status %i", status.si_code, status.si_status);
 199         return status.si_status;
 200 }