src/shared/pager.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2010 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <signal.h>
  22 #include <stddef.h>
  23 #include <stdint.h>
  24 #include <stdio.h>
  25 #include <stdlib.h>
  26 #include <string.h>
  27 #include <sys/prctl.h>
  28 #include <unistd.h>
  29
  30 #include "copy.h"
  31 #include "fd-util.h"
  32 #include "locale-util.h"
  33 #include "log.h"
  34 #include "macro.h"
  35 #include "pager.h"
  36 #include "process-util.h"
  37 #include "signal-util.h"
  38 #include "string-util.h"
  39 #include "terminal-util.h"
  40
  41 static pid_t pager_pid = 0;
  42
  43 noreturn static void pager_fallback(void) {
  44         int r;
  45
  46         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, (uint64_t) -1, false);
  47         if (r < 0) {
  48                 log_error_errno(r, "Internal pager failed: %m");
  49                 _exit(EXIT_FAILURE);
  50         }
  51
  52         _exit(EXIT_SUCCESS);
  53 }
  54
  55 int pager_open(bool no_pager, bool jump_to_end) {
  56         _cleanup_close_pair_ int fd[2] = { -1, -1 };
  57         const char *pager;
  58         pid_t parent_pid;
  59
  60         if (no_pager)
  61                 return 0;
  62
  63         if (pager_pid > 0)
  64                 return 1;
  65
  66         if (!on_tty())
  67                 return 0;
  68
  69         pager = getenv("SYSTEMD_PAGER");
  70         if (!pager)
  71                 pager = getenv("PAGER");
  72
  73         /* If the pager is explicitly turned off, honour it */
  74         if (pager && (pager[0] == 0 || streq(pager, "cat")))
  75                 return 0;
  76
  77         /* Determine and cache number of columns before we spawn the
  78          * pager so that we get the value from the actual tty */
  79         (void) columns();
  80
  81         if (pipe(fd) < 0)
  82                 return log_error_errno(errno, "Failed to create pager pipe: %m");
  83
  84         parent_pid = getpid();
  85
  86         pager_pid = fork();
  87         if (pager_pid < 0)
  88                 return log_error_errno(errno, "Failed to fork pager: %m");
  89
  90         /* In the child start the pager */
  91         if (pager_pid == 0) {
  92                 const char* less_opts, *less_charset;
  93
  94                 (void) reset_all_signal_handlers();
  95                 (void) reset_signal_mask();
  96
  97                 (void) dup2(fd[0], STDIN_FILENO);
  98                 safe_close_pair(fd);
  99
 100                 /* Initialize a good set of less options */
 101                 less_opts = getenv("SYSTEMD_LESS");
 102                 if (!less_opts)
 103                         less_opts = "FRSXMK";
 104                 if (jump_to_end)
 105                         less_opts = strjoina(less_opts, " +G");
 106                 setenv("LESS", less_opts, 1);
 107
 108                 /* Initialize a good charset for less. This is
 109                  * particularly important if we output UTF-8
 110                  * characters. */
 111                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 112                 if (!less_charset && is_locale_utf8())
 113                         less_charset = "utf-8";
 114                 if (less_charset)
 115                         setenv("LESSCHARSET", less_charset, 1);
 116
 117                 /* Make sure the pager goes away when the parent dies */
 118                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
 119                         _exit(EXIT_FAILURE);
 120
 121                 /* Check whether our parent died before we were able
 122                  * to set the death signal */
 123                 if (getppid() != parent_pid)
 124                         _exit(EXIT_SUCCESS);
 125
 126                 if (pager) {
 127                         execlp(pager, pager, NULL);
 128                         execl("/bin/sh", "sh", "-c", pager, NULL);
 129                 }
 130
 131                 /* Debian's alternatives command for pagers is
 132                  * called 'pager'. Note that we do not call
 133                  * sensible-pagers here, since that is just a
 134                  * shell script that implements a logic that
 135                  * is similar to this one anyway, but is
 136                  * Debian-specific. */
 137                 execlp("pager", "pager", NULL);
 138
 139                 execlp("less", "less", NULL);
 140                 execlp("more", "more", NULL);
 141
 142                 pager_fallback();
 143                 /* not reached */
 144         }
 145
 146         /* Return in the parent */
 147         if (dup2(fd[1], STDOUT_FILENO) < 0)
 148                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 149         if (dup2(fd[1], STDERR_FILENO) < 0)
 150                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 151
 152         return 1;
 153 }
 154
 155 void pager_close(void) {
 156
 157         if (pager_pid <= 0)
 158                 return;
 159
 160         /* Inform pager that we are done */
 161         stdout = safe_fclose(stdout);
 162         stderr = safe_fclose(stderr);
 163
 164         (void) kill(pager_pid, SIGCONT);
 165         (void) wait_for_terminate(pager_pid, NULL);
 166         pager_pid = 0;
 167 }
 168
 169 bool pager_have(void) {
 170         return pager_pid > 0;
 171 }
 172
 173 int show_man_page(const char *desc, bool null_stdio) {
 174         const char *args[4] = { "man", NULL, NULL, NULL };
 175         char *e = NULL;
 176         pid_t pid;
 177         size_t k;
 178         int r;
 179         siginfo_t status;
 180
 181         k = strlen(desc);
 182
 183         if (desc[k-1] == ')')
 184                 e = strrchr(desc, '(');
 185
 186         if (e) {
 187                 char *page = NULL, *section = NULL;
 188
 189                 page = strndupa(desc, e - desc);
 190                 section = strndupa(e + 1, desc + k - e - 2);
 191
 192                 args[1] = section;
 193                 args[2] = page;
 194         } else
 195                 args[1] = desc;
 196
 197         pid = fork();
 198         if (pid < 0)
 199                 return log_error_errno(errno, "Failed to fork: %m");
 200
 201         if (pid == 0) {
 202                 /* Child */
 203
 204                 (void) reset_all_signal_handlers();
 205                 (void) reset_signal_mask();
 206
 207                 if (null_stdio) {
 208                         r = make_null_stdio();
 209                         if (r < 0) {
 210                                 log_error_errno(r, "Failed to kill stdio: %m");
 211                                 _exit(EXIT_FAILURE);
 212                         }
 213                 }
 214
 215                 execvp(args[0], (char**) args);
 216                 log_error_errno(errno, "Failed to execute man: %m");
 217                 _exit(EXIT_FAILURE);
 218         }
 219
 220         r = wait_for_terminate(pid, &status);
 221         if (r < 0)
 222                 return r;
 223
 224         log_debug("Exit code %i status %i", status.si_code, status.si_status);
 225         return status.si_status;
 226 }