src/basic/pager.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <signal.h>
   5 #include <stddef.h>
   6 #include <stdint.h>
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <string.h>
  10 #include <sys/prctl.h>
  11 #include <unistd.h>
  12
  13 #include "copy.h"
  14 #include "fd-util.h"
  15 #include "locale-util.h"
  16 #include "log.h"
  17 #include "macro.h"
  18 #include "pager.h"
  19 #include "process-util.h"
  20 #include "signal-util.h"
  21 #include "string-util.h"
  22 #include "strv.h"
  23 #include "terminal-util.h"
  24
  25 static pid_t pager_pid = 0;
  26
  27 static int stored_stdout = -1;
  28 static int stored_stderr = -1;
  29 static bool stdout_redirected = false;
  30 static bool stderr_redirected = false;
  31
  32 _noreturn_ static void pager_fallback(void) {
  33         int r;
  34
  35         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, (uint64_t) -1, 0);
  36         if (r < 0) {
  37                 log_error_errno(r, "Internal pager failed: %m");
  38                 _exit(EXIT_FAILURE);
  39         }
  40
  41         _exit(EXIT_SUCCESS);
  42 }
  43
  44 int pager_open(bool no_pager, bool jump_to_end) {
  45         _cleanup_close_pair_ int fd[2] = { -1, -1 };
  46         const char *pager;
  47         int r;
  48
  49         if (no_pager)
  50                 return 0;
  51
  52         if (pager_pid > 0)
  53                 return 1;
  54
  55         if (terminal_is_dumb())
  56                 return 0;
  57
  58         if (!is_main_thread())
  59                 return -EPERM;
  60
  61         pager = getenv("SYSTEMD_PAGER");
  62         if (!pager)
  63                 pager = getenv("PAGER");
  64
  65         /* If the pager is explicitly turned off, honour it */
  66         if (pager && STR_IN_SET(pager, "", "cat"))
  67                 return 0;
  68
  69         /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the
  70          * actual tty */
  71         (void) columns();
  72         (void) lines();
  73
  74         if (pipe2(fd, O_CLOEXEC) < 0)
  75                 return log_error_errno(errno, "Failed to create pager pipe: %m");
  76
  77         r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_LOG, &pager_pid);
  78         if (r < 0)
  79                 return r;
  80         if (r == 0) {
  81                 const char* less_opts, *less_charset;
  82
  83                 /* In the child start the pager */
  84
  85                 (void) dup2(fd[0], STDIN_FILENO);
  86                 safe_close_pair(fd);
  87
  88                 /* Initialize a good set of less options */
  89                 less_opts = getenv("SYSTEMD_LESS");
  90                 if (!less_opts)
  91                         less_opts = "FRSXMK";
  92                 if (jump_to_end)
  93                         less_opts = strjoina(less_opts, " +G");
  94                 if (setenv("LESS", less_opts, 1) < 0)
  95                         _exit(EXIT_FAILURE);
  96
  97                 /* Initialize a good charset for less. This is
  98                  * particularly important if we output UTF-8
  99                  * characters. */
 100                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 101                 if (!less_charset && is_locale_utf8())
 102                         less_charset = "utf-8";
 103                 if (less_charset &&
 104                     setenv("LESSCHARSET", less_charset, 1) < 0)
 105                         _exit(EXIT_FAILURE);
 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         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 129         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 130                 stored_stdout = safe_close(stored_stdout);
 131                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 132         }
 133         stdout_redirected = true;
 134
 135         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 136         if (dup2(fd[1], STDERR_FILENO) < 0) {
 137                 stored_stderr = safe_close(stored_stderr);
 138                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 139         }
 140         stderr_redirected = true;
 141
 142         return 1;
 143 }
 144
 145 void pager_close(void) {
 146
 147         if (pager_pid <= 0)
 148                 return;
 149
 150         /* Inform pager that we are done */
 151         (void) fflush(stdout);
 152         if (stdout_redirected)
 153                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 154                         (void) close(STDOUT_FILENO);
 155         stored_stdout = safe_close(stored_stdout);
 156         (void) fflush(stderr);
 157         if (stderr_redirected)
 158                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 159                         (void) close(STDERR_FILENO);
 160         stored_stderr = safe_close(stored_stderr);
 161         stdout_redirected = stderr_redirected = false;
 162
 163         (void) kill(pager_pid, SIGCONT);
 164         (void) wait_for_terminate(pager_pid, NULL);
 165         pager_pid = 0;
 166 }
 167
 168 bool pager_have(void) {
 169         return pager_pid > 0;
 170 }
 171
 172 int show_man_page(const char *desc, bool null_stdio) {
 173         const char *args[4] = { "man", NULL, NULL, NULL };
 174         char *e = NULL;
 175         pid_t pid;
 176         size_t k;
 177         int r;
 178
 179         k = strlen(desc);
 180
 181         if (desc[k-1] == ')')
 182                 e = strrchr(desc, '(');
 183
 184         if (e) {
 185                 char *page = NULL, *section = NULL;
 186
 187                 page = strndupa(desc, e - desc);
 188                 section = strndupa(e + 1, desc + k - e - 2);
 189
 190                 args[1] = section;
 191                 args[2] = page;
 192         } else
 193                 args[1] = desc;
 194
 195         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG|(null_stdio ? FORK_NULL_STDIO : 0)|FORK_LOG, &pid);
 196         if (r < 0)
 197                 return r;
 198         if (r == 0) {
 199                 /* Child */
 200                 execvp(args[0], (char**) args);
 201                 log_error_errno(errno, "Failed to execute man: %m");
 202                 _exit(EXIT_FAILURE);
 203         }
 204
 205         return wait_for_terminate_and_check(NULL, pid, 0);
 206 }