src/shared/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 "fileio.h"
  16 #include "io-util.h"
  17 #include "locale-util.h"
  18 #include "log.h"
  19 #include "macro.h"
  20 #include "pager.h"
  21 #include "process-util.h"
  22 #include "rlimit-util.h"
  23 #include "signal-util.h"
  24 #include "string-util.h"
  25 #include "strv.h"
  26 #include "terminal-util.h"
  27
  28 static pid_t pager_pid = 0;
  29
  30 static int stored_stdout = -1;
  31 static int stored_stderr = -1;
  32 static bool stdout_redirected = false;
  33 static bool stderr_redirected = false;
  34
  35 _noreturn_ static void pager_fallback(void) {
  36         int r;
  37
  38         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, (uint64_t) -1, 0);
  39         if (r < 0) {
  40                 log_error_errno(r, "Internal pager failed: %m");
  41                 _exit(EXIT_FAILURE);
  42         }
  43
  44         _exit(EXIT_SUCCESS);
  45 }
  46
  47 static int no_quit_on_interrupt(int exe_name_fd, const char *less_opts) {
  48         _cleanup_fclose_ FILE *file = NULL;
  49         _cleanup_free_ char *line = NULL;
  50         int r;
  51
  52         assert(exe_name_fd >= 0);
  53         assert(less_opts);
  54
  55         /* This takes ownership of exe_name_fd */
  56         file = fdopen(exe_name_fd, "r");
  57         if (!file) {
  58                 safe_close(exe_name_fd);
  59                 return log_debug_errno(errno, "Failed to create FILE object: %m");
  60         }
  61
  62         /* Find the last line */
  63         for (;;) {
  64                 _cleanup_free_ char *t = NULL;
  65
  66                 r = read_line(file, LONG_LINE_MAX, &t);
  67                 if (r < 0)
  68                         return r;
  69                 if (r == 0)
  70                         break;
  71
  72                 free_and_replace(line, t);
  73         }
  74
  75         /* We only treat "less" specially.
  76          * Return true whenever option K is *not* set. */
  77         r = streq_ptr(line, "less") && !strchr(less_opts, 'K');
  78
  79         log_debug("Pager executable is \"%s\", options \"%s\", quit_on_interrupt: %s",
  80                   strnull(line), less_opts, yes_no(!r));
  81         return r;
  82 }
  83
  84 int pager_open(PagerFlags flags) {
  85         _cleanup_close_pair_ int fd[2] = { -1, -1 }, exe_name_pipe[2] = { -1, -1 };
  86         _cleanup_strv_free_ char **pager_args = NULL;
  87         const char *pager, *less_opts;
  88         int r;
  89
  90         if (flags & PAGER_DISABLE)
  91                 return 0;
  92
  93         if (pager_pid > 0)
  94                 return 1;
  95
  96         if (terminal_is_dumb())
  97                 return 0;
  98
  99         if (!is_main_thread())
 100                 return -EPERM;
 101
 102         pager = getenv("SYSTEMD_PAGER");
 103         if (!pager)
 104                 pager = getenv("PAGER");
 105
 106         if (pager) {
 107                 pager_args = strv_split(pager, WHITESPACE);
 108                 if (!pager_args)
 109                         return -ENOMEM;
 110
 111                 /* If the pager is explicitly turned off, honour it */
 112                 if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat")))
 113                         return 0;
 114         }
 115
 116         /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the
 117          * actual tty */
 118         (void) columns();
 119         (void) lines();
 120
 121         if (pipe2(fd, O_CLOEXEC) < 0)
 122                 return log_error_errno(errno, "Failed to create pager pipe: %m");
 123
 124         /* This is a pipe to feed the name of the executed pager binary into the parent */
 125         if (pipe2(exe_name_pipe, O_CLOEXEC) < 0)
 126                 return log_error_errno(errno, "Failed to create exe_name pipe: %m");
 127
 128         /* Initialize a good set of less options */
 129         less_opts = getenv("SYSTEMD_LESS");
 130         if (!less_opts)
 131                 less_opts = "FRSXMK";
 132         if (flags & PAGER_JUMP_TO_END)
 133                 less_opts = strjoina(less_opts, " +G");
 134
 135         r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_LOG, &pager_pid);
 136         if (r < 0)
 137                 return r;
 138         if (r == 0) {
 139                 const char *less_charset, *exe;
 140
 141                 /* In the child start the pager */
 142
 143                 (void) dup2(fd[0], STDIN_FILENO);
 144                 safe_close_pair(fd);
 145
 146                 if (setenv("LESS", less_opts, 1) < 0)
 147                         _exit(EXIT_FAILURE);
 148
 149                 /* Initialize a good charset for less. This is
 150                  * particularly important if we output UTF-8
 151                  * characters. */
 152                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 153                 if (!less_charset && is_locale_utf8())
 154                         less_charset = "utf-8";
 155                 if (less_charset &&
 156                     setenv("LESSCHARSET", less_charset, 1) < 0)
 157                         _exit(EXIT_FAILURE);
 158
 159                 if (pager_args) {
 160                         if (loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1, false) < 0)
 161                                 _exit(EXIT_FAILURE);
 162
 163                         execvp(pager_args[0], pager_args);
 164                 }
 165
 166                 /* Debian's alternatives command for pagers is
 167                  * called 'pager'. Note that we do not call
 168                  * sensible-pagers here, since that is just a
 169                  * shell script that implements a logic that
 170                  * is similar to this one anyway, but is
 171                  * Debian-specific. */
 172                 FOREACH_STRING(exe, "pager", "less", "more") {
 173                         if (loop_write(exe_name_pipe[1], exe, strlen(exe) + 1, false) < 0)
 174                                 _exit(EXIT_FAILURE);
 175                         execlp(exe, exe, NULL);
 176                 }
 177
 178                 if (loop_write(exe_name_pipe[1], "(built-in)", strlen("(built-in") + 1, false) < 0)
 179                         _exit(EXIT_FAILURE);
 180                 pager_fallback();
 181                 /* not reached */
 182         }
 183
 184         /* Return in the parent */
 185         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 186         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 187                 stored_stdout = safe_close(stored_stdout);
 188                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 189         }
 190         stdout_redirected = true;
 191
 192         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 193         if (dup2(fd[1], STDERR_FILENO) < 0) {
 194                 stored_stderr = safe_close(stored_stderr);
 195                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 196         }
 197         stderr_redirected = true;
 198
 199         exe_name_pipe[1] = safe_close(exe_name_pipe[1]);
 200
 201         r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts);
 202         if (r < 0)
 203                 return r;
 204         if (r > 0)
 205                 (void) ignore_signals(SIGINT, -1);
 206
 207         return 1;
 208 }
 209
 210 void pager_close(void) {
 211
 212         if (pager_pid <= 0)
 213                 return;
 214
 215         /* Inform pager that we are done */
 216         (void) fflush(stdout);
 217         if (stdout_redirected)
 218                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 219                         (void) close(STDOUT_FILENO);
 220         stored_stdout = safe_close(stored_stdout);
 221         (void) fflush(stderr);
 222         if (stderr_redirected)
 223                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 224                         (void) close(STDERR_FILENO);
 225         stored_stderr = safe_close(stored_stderr);
 226         stdout_redirected = stderr_redirected = false;
 227
 228         (void) kill(pager_pid, SIGCONT);
 229         (void) wait_for_terminate(pager_pid, NULL);
 230         pager_pid = 0;
 231 }
 232
 233 bool pager_have(void) {
 234         return pager_pid > 0;
 235 }
 236
 237 int show_man_page(const char *desc, bool null_stdio) {
 238         const char *args[4] = { "man", NULL, NULL, NULL };
 239         char *e = NULL;
 240         pid_t pid;
 241         size_t k;
 242         int r;
 243
 244         k = strlen(desc);
 245
 246         if (desc[k-1] == ')')
 247                 e = strrchr(desc, '(');
 248
 249         if (e) {
 250                 char *page = NULL, *section = NULL;
 251
 252                 page = strndupa(desc, e - desc);
 253                 section = strndupa(e + 1, desc + k - e - 2);
 254
 255                 args[1] = section;
 256                 args[2] = page;
 257         } else
 258                 args[1] = desc;
 259
 260         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG|(null_stdio ? FORK_NULL_STDIO : 0)|FORK_LOG, &pid);
 261         if (r < 0)
 262                 return r;
 263         if (r == 0) {
 264                 /* Child */
 265                 execvp(args[0], (char**) args);
 266                 log_error_errno(errno, "Failed to execute man: %m");
 267                 _exit(EXIT_FAILURE);
 268         }
 269
 270         return wait_for_terminate_and_check(NULL, pid, 0);
 271 }