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 #include "util.h"
  28
  29 static pid_t pager_pid = 0;
  30
  31 static int stored_stdout = -1;
  32 static int stored_stderr = -1;
  33 static bool stdout_redirected = false;
  34 static bool stderr_redirected = false;
  35
  36 _noreturn_ static void pager_fallback(void) {
  37         int r;
  38
  39         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, (uint64_t) -1, 0);
  40         if (r < 0) {
  41                 log_error_errno(r, "Internal pager failed: %m");
  42                 _exit(EXIT_FAILURE);
  43         }
  44
  45         _exit(EXIT_SUCCESS);
  46 }
  47
  48 static int no_quit_on_interrupt(int exe_name_fd, const char *less_opts) {
  49         _cleanup_fclose_ FILE *file = NULL;
  50         _cleanup_free_ char *line = NULL;
  51         int r;
  52
  53         assert(exe_name_fd >= 0);
  54         assert(less_opts);
  55
  56         /* This takes ownership of exe_name_fd */
  57         file = fdopen(exe_name_fd, "r");
  58         if (!file) {
  59                 safe_close(exe_name_fd);
  60                 return log_error_errno(errno, "Failed to create FILE object: %m");
  61         }
  62
  63         /* Find the last line */
  64         for (;;) {
  65                 _cleanup_free_ char *t = NULL;
  66
  67                 r = read_line(file, LONG_LINE_MAX, &t);
  68                 if (r < 0)
  69                         return log_error_errno(r, "Failed to read from socket: %m");
  70                 if (r == 0)
  71                         break;
  72
  73                 free_and_replace(line, t);
  74         }
  75
  76         /* We only treat "less" specially.
  77          * Return true whenever option K is *not* set. */
  78         r = streq_ptr(line, "less") && !strchr(less_opts, 'K');
  79
  80         log_debug("Pager executable is \"%s\", options \"%s\", quit_on_interrupt: %s",
  81                   strnull(line), less_opts, yes_no(!r));
  82         return r;
  83 }
  84
  85 int pager_open(PagerFlags flags) {
  86         _cleanup_close_pair_ int fd[2] = { -1, -1 }, exe_name_pipe[2] = { -1, -1 };
  87         _cleanup_strv_free_ char **pager_args = NULL;
  88         const char *pager, *less_opts;
  89         int r;
  90
  91         if (flags & PAGER_DISABLE)
  92                 return 0;
  93
  94         if (pager_pid > 0)
  95                 return 1;
  96
  97         if (terminal_is_dumb())
  98                 return 0;
  99
 100         if (!is_main_thread())
 101                 return log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread.");
 102
 103         pager = getenv("SYSTEMD_PAGER");
 104         if (!pager)
 105                 pager = getenv("PAGER");
 106
 107         if (pager) {
 108                 pager_args = strv_split(pager, WHITESPACE);
 109                 if (!pager_args)
 110                         return log_oom();
 111
 112                 /* If the pager is explicitly turned off, honour it */
 113                 if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat")))
 114                         return 0;
 115         }
 116
 117         /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the
 118          * actual tty */
 119         (void) columns();
 120         (void) lines();
 121
 122         if (pipe2(fd, O_CLOEXEC) < 0)
 123                 return log_error_errno(errno, "Failed to create pager pipe: %m");
 124
 125         /* This is a pipe to feed the name of the executed pager binary into the parent */
 126         if (pipe2(exe_name_pipe, O_CLOEXEC) < 0)
 127                 return log_error_errno(errno, "Failed to create exe_name pipe: %m");
 128
 129         /* Initialize a good set of less options */
 130         less_opts = getenv("SYSTEMD_LESS");
 131         if (!less_opts)
 132                 less_opts = "FRSXMK";
 133         if (flags & PAGER_JUMP_TO_END)
 134                 less_opts = strjoina(less_opts, " +G");
 135
 136         r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pager_pid);
 137         if (r < 0)
 138                 return r;
 139         if (r == 0) {
 140                 const char *less_charset, *exe;
 141
 142                 /* In the child start the pager */
 143
 144                 if (dup2(fd[0], STDIN_FILENO) < 0) {
 145                         log_error_errno(errno, "Failed to duplicate file descriptor to STDIN: %m");
 146                         _exit(EXIT_FAILURE);
 147                 }
 148
 149                 safe_close_pair(fd);
 150
 151                 if (setenv("LESS", less_opts, 1) < 0) {
 152                         log_error_errno(errno, "Failed to set environment variable LESS: %m");
 153                         _exit(EXIT_FAILURE);
 154                 }
 155
 156                 /* Initialize a good charset for less. This is
 157                  * particularly important if we output UTF-8
 158                  * characters. */
 159                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 160                 if (!less_charset && is_locale_utf8())
 161                         less_charset = "utf-8";
 162                 if (less_charset &&
 163                     setenv("LESSCHARSET", less_charset, 1) < 0) {
 164                         log_error_errno(errno, "Failed to set environment variable LESSCHARSET: %m");
 165                         _exit(EXIT_FAILURE);
 166                 }
 167
 168                 if (pager_args) {
 169                         r = loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1, false);
 170                         if (r < 0) {
 171                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 172                                 _exit(EXIT_FAILURE);
 173                         }
 174
 175                         execvp(pager_args[0], pager_args);
 176                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 177                                        "Failed to execute '%s', using fallback pagers: %m", pager_args[0]);
 178                 }
 179
 180                 /* Debian's alternatives command for pagers is
 181                  * called 'pager'. Note that we do not call
 182                  * sensible-pagers here, since that is just a
 183                  * shell script that implements a logic that
 184                  * is similar to this one anyway, but is
 185                  * Debian-specific. */
 186                 FOREACH_STRING(exe, "pager", "less", "more") {
 187                         r = loop_write(exe_name_pipe[1], exe, strlen(exe) + 1, false);
 188                         if (r  < 0) {
 189                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 190                                 _exit(EXIT_FAILURE);
 191                         }
 192                         execlp(exe, exe, NULL);
 193                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 194                                        "Failed to execute '%s', using next fallback pager: %m", exe);
 195                 }
 196
 197                 r = loop_write(exe_name_pipe[1], "(built-in)", strlen("(built-in") + 1, false);
 198                 if (r < 0) {
 199                         log_error_errno(r, "Failed to write pager name to socket: %m");
 200                         _exit(EXIT_FAILURE);
 201                 }
 202                 pager_fallback();
 203                 /* not reached */
 204         }
 205
 206         /* Return in the parent */
 207         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 208         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 209                 stored_stdout = safe_close(stored_stdout);
 210                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 211         }
 212         stdout_redirected = true;
 213
 214         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 215         if (dup2(fd[1], STDERR_FILENO) < 0) {
 216                 stored_stderr = safe_close(stored_stderr);
 217                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 218         }
 219         stderr_redirected = true;
 220
 221         exe_name_pipe[1] = safe_close(exe_name_pipe[1]);
 222
 223         r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts);
 224         if (r < 0)
 225                 return r;
 226         if (r > 0)
 227                 (void) ignore_signals(SIGINT, -1);
 228
 229         return 1;
 230 }
 231
 232 void pager_close(void) {
 233
 234         if (pager_pid <= 0)
 235                 return;
 236
 237         /* Inform pager that we are done */
 238         (void) fflush(stdout);
 239         if (stdout_redirected)
 240                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 241                         (void) close(STDOUT_FILENO);
 242         stored_stdout = safe_close(stored_stdout);
 243         (void) fflush(stderr);
 244         if (stderr_redirected)
 245                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 246                         (void) close(STDERR_FILENO);
 247         stored_stderr = safe_close(stored_stderr);
 248         stdout_redirected = stderr_redirected = false;
 249
 250         (void) kill(pager_pid, SIGCONT);
 251         (void) wait_for_terminate(pager_pid, NULL);
 252         pager_pid = 0;
 253 }
 254
 255 bool pager_have(void) {
 256         return pager_pid > 0;
 257 }
 258
 259 int show_man_page(const char *desc, bool null_stdio) {
 260         const char *args[4] = { "man", NULL, NULL, NULL };
 261         char *e = NULL;
 262         pid_t pid;
 263         size_t k;
 264         int r;
 265
 266         k = strlen(desc);
 267
 268         if (desc[k-1] == ')')
 269                 e = strrchr(desc, '(');
 270
 271         if (e) {
 272                 char *page = NULL, *section = NULL;
 273
 274                 page = strndupa(desc, e - desc);
 275                 section = strndupa(e + 1, desc + k - e - 2);
 276
 277                 args[1] = section;
 278                 args[2] = page;
 279         } else
 280                 args[1] = desc;
 281
 282         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG|(null_stdio ? FORK_NULL_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
 283         if (r < 0)
 284                 return r;
 285         if (r == 0) {
 286                 /* Child */
 287                 execvp(args[0], (char**) args);
 288                 log_error_errno(errno, "Failed to execute man: %m");
 289                 _exit(EXIT_FAILURE);
 290         }
 291
 292         return wait_for_terminate_and_check(NULL, pid, 0);
 293 }