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 jump_to_end) {
  56         _cleanup_close_pair_ int fd[2] = { -1, -1 };
  57         const char *pager;
  58         pid_t parent_pid;
  59
  60         if (pager_pid > 0)
  61                 return 1;
  62
  63         if (!on_tty())
  64                 return 0;
  65
  66         pager = getenv("SYSTEMD_PAGER");
  67         if (!pager)
  68                 pager = getenv("PAGER");
  69
  70         /* If the pager is explicitly turned off, honour it */
  71         if (pager && (pager[0] == 0 || streq(pager, "cat")))
  72                 return 0;
  73
  74         /* Determine and cache number of columns before we spawn the
  75          * pager so that we get the value from the actual tty */
  76         (void) columns();
  77
  78         if (pipe(fd) < 0)
  79                 return log_error_errno(errno, "Failed to create pager pipe: %m");
  80
  81         parent_pid = getpid();
  82
  83         pager_pid = fork();
  84         if (pager_pid < 0)
  85                 return log_error_errno(errno, "Failed to fork pager: %m");
  86
  87         /* In the child start the pager */
  88         if (pager_pid == 0) {
  89                 const char* less_opts, *less_charset;
  90
  91                 (void) reset_all_signal_handlers();
  92                 (void) reset_signal_mask();
  93
  94                 (void) dup2(fd[0], STDIN_FILENO);
  95                 safe_close_pair(fd);
  96
  97                 /* Initialize a good set of less options */
  98                 less_opts = getenv("SYSTEMD_LESS");
  99                 if (!less_opts)
 100                         less_opts = "FRSXMK";
 101                 if (jump_to_end)
 102                         less_opts = strjoina(less_opts, " +G");
 103                 setenv("LESS", less_opts, 1);
 104
 105                 /* Initialize a good charset for less. This is
 106                  * particularly important if we output UTF-8
 107                  * characters. */
 108                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 109                 if (!less_charset && is_locale_utf8())
 110                         less_charset = "utf-8";
 111                 if (less_charset)
 112                         setenv("LESSCHARSET", less_charset, 1);
 113
 114                 /* Make sure the pager goes away when the parent dies */
 115                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
 116                         _exit(EXIT_FAILURE);
 117
 118                 /* Check whether our parent died before we were able
 119                  * to set the death signal */
 120                 if (getppid() != parent_pid)
 121                         _exit(EXIT_SUCCESS);
 122
 123                 if (pager) {
 124                         execlp(pager, pager, NULL);
 125                         execl("/bin/sh", "sh", "-c", pager, NULL);
 126                 }
 127
 128                 /* Debian's alternatives command for pagers is
 129                  * called 'pager'. Note that we do not call
 130                  * sensible-pagers here, since that is just a
 131                  * shell script that implements a logic that
 132                  * is similar to this one anyway, but is
 133                  * Debian-specific. */
 134                 execlp("pager", "pager", NULL);
 135
 136                 execlp("less", "less", NULL);
 137                 execlp("more", "more", NULL);
 138
 139                 pager_fallback();
 140                 /* not reached */
 141         }
 142
 143         /* Return in the parent */
 144         if (dup2(fd[1], STDOUT_FILENO) < 0)
 145                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 146         if (dup2(fd[1], STDERR_FILENO) < 0)
 147                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 148
 149         return 1;
 150 }
 151
 152 void pager_close(void) {
 153
 154         if (pager_pid <= 0)
 155                 return;
 156
 157         /* Inform pager that we are done */
 158         stdout = safe_fclose(stdout);
 159         stderr = safe_fclose(stderr);
 160
 161         (void) kill(pager_pid, SIGCONT);
 162         (void) wait_for_terminate(pager_pid, NULL);
 163         pager_pid = 0;
 164 }
 165
 166 bool pager_have(void) {
 167         return pager_pid > 0;
 168 }
 169
 170 int show_man_page(const char *desc, bool null_stdio) {
 171         const char *args[4] = { "man", NULL, NULL, NULL };
 172         char *e = NULL;
 173         pid_t pid;
 174         size_t k;
 175         int r;
 176         siginfo_t status;
 177
 178         k = strlen(desc);
 179
 180         if (desc[k-1] == ')')
 181                 e = strrchr(desc, '(');
 182
 183         if (e) {
 184                 char *page = NULL, *section = NULL;
 185
 186                 page = strndupa(desc, e - desc);
 187                 section = strndupa(e + 1, desc + k - e - 2);
 188
 189                 args[1] = section;
 190                 args[2] = page;
 191         } else
 192                 args[1] = desc;
 193
 194         pid = fork();
 195         if (pid < 0)
 196                 return log_error_errno(errno, "Failed to fork: %m");
 197
 198         if (pid == 0) {
 199                 /* Child */
 200
 201                 (void) reset_all_signal_handlers();
 202                 (void) reset_signal_mask();
 203
 204                 if (null_stdio) {
 205                         r = make_null_stdio();
 206                         if (r < 0) {
 207                                 log_error_errno(r, "Failed to kill stdio: %m");
 208                                 _exit(EXIT_FAILURE);
 209                         }
 210                 }
 211
 212                 execvp(args[0], (char**) args);
 213                 log_error_errno(errno, "Failed to execute man: %m");
 214                 _exit(EXIT_FAILURE);
 215         }
 216
 217         r = wait_for_terminate(pid, &status);
 218         if (r < 0)
 219                 return r;
 220
 221         log_debug("Exit code %i status %i", status.si_code, status.si_status);
 222         return status.si_status;
 223 }