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