src/shared/pager.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <stddef.h>
   5 #include <stdint.h>
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <sys/prctl.h>
   9 #include <unistd.h>
  10
  11 #include "copy.h"
  12 #include "fd-util.h"
  13 #include "fileio.h"
  14 #include "io-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 "rlimit-util.h"
  21 #include "signal-util.h"
  22 #include "string-util.h"
  23 #include "strv.h"
  24 #include "terminal-util.h"
  25 #include "util.h"
  26
  27 static pid_t pager_pid = 0;
  28
  29 static int stored_stdout = -1;
  30 static int stored_stderr = -1;
  31 static bool stdout_redirected = false;
  32 static bool stderr_redirected = false;
  33
  34 _noreturn_ static void pager_fallback(void) {
  35         int r;
  36
  37         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, (uint64_t) -1, 0);
  38         if (r < 0) {
  39                 log_error_errno(r, "Internal pager failed: %m");
  40                 _exit(EXIT_FAILURE);
  41         }
  42
  43         _exit(EXIT_SUCCESS);
  44 }
  45
  46 static int no_quit_on_interrupt(int exe_name_fd, const char *less_opts) {
  47         _cleanup_fclose_ FILE *file = NULL;
  48         _cleanup_free_ char *line = NULL;
  49         int r;
  50
  51         assert(exe_name_fd >= 0);
  52         assert(less_opts);
  53
  54         /* This takes ownership of exe_name_fd */
  55         file = fdopen(exe_name_fd, "r");
  56         if (!file) {
  57                 safe_close(exe_name_fd);
  58                 return log_error_errno(errno, "Failed to create FILE object: %m");
  59         }
  60
  61         /* Find the last line */
  62         for (;;) {
  63                 _cleanup_free_ char *t = NULL;
  64
  65                 r = read_line(file, LONG_LINE_MAX, &t);
  66                 if (r < 0)
  67                         return log_error_errno(r, "Failed to read from socket: %m");
  68                 if (r == 0)
  69                         break;
  70
  71                 free_and_replace(line, t);
  72         }
  73
  74         /* We only treat "less" specially.
  75          * Return true whenever option K is *not* set. */
  76         r = streq_ptr(line, "less") && !strchr(less_opts, 'K');
  77
  78         log_debug("Pager executable is \"%s\", options \"%s\", quit_on_interrupt: %s",
  79                   strnull(line), less_opts, yes_no(!r));
  80         return r;
  81 }
  82
  83 int pager_open(PagerFlags flags) {
  84         _cleanup_close_pair_ int fd[2] = { -1, -1 }, exe_name_pipe[2] = { -1, -1 };
  85         _cleanup_strv_free_ char **pager_args = NULL;
  86         const char *pager, *less_opts;
  87         int r;
  88
  89         if (flags & PAGER_DISABLE)
  90                 return 0;
  91
  92         if (pager_pid > 0)
  93                 return 1;
  94
  95         if (terminal_is_dumb())
  96                 return 0;
  97
  98         if (!is_main_thread())
  99                 return log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread.");
 100
 101         pager = getenv("SYSTEMD_PAGER");
 102         if (!pager)
 103                 pager = getenv("PAGER");
 104
 105         if (pager) {
 106                 pager_args = strv_split(pager, WHITESPACE);
 107                 if (!pager_args)
 108                         return log_oom();
 109
 110                 /* If the pager is explicitly turned off, honour it */
 111                 if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat")))
 112                         return 0;
 113         }
 114
 115         /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the
 116          * actual tty */
 117         (void) columns();
 118         (void) lines();
 119
 120         if (pipe2(fd, O_CLOEXEC) < 0)
 121                 return log_error_errno(errno, "Failed to create pager pipe: %m");
 122
 123         /* This is a pipe to feed the name of the executed pager binary into the parent */
 124         if (pipe2(exe_name_pipe, O_CLOEXEC) < 0)
 125                 return log_error_errno(errno, "Failed to create exe_name pipe: %m");
 126
 127         /* Initialize a good set of less options */
 128         less_opts = getenv("SYSTEMD_LESS");
 129         if (!less_opts)
 130                 less_opts = "FRSXMK";
 131         if (flags & PAGER_JUMP_TO_END)
 132                 less_opts = strjoina(less_opts, " +G");
 133
 134         /* We set SIGINT as PR_DEATHSIG signal here, to match the "K" parameter we set in $LESS, which enables SIGINT behaviour. */
 135         r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGINT|FORK_RLIMIT_NOFILE_SAFE|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                 if (dup2(fd[0], STDIN_FILENO) < 0) {
 144                         log_error_errno(errno, "Failed to duplicate file descriptor to STDIN: %m");
 145                         _exit(EXIT_FAILURE);
 146                 }
 147
 148                 safe_close_pair(fd);
 149
 150                 if (setenv("LESS", less_opts, 1) < 0) {
 151                         log_error_errno(errno, "Failed to set environment variable LESS: %m");
 152                         _exit(EXIT_FAILURE);
 153                 }
 154
 155                 /* Initialize a good charset for less. This is
 156                  * particularly important if we output UTF-8
 157                  * characters. */
 158                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 159                 if (!less_charset && is_locale_utf8())
 160                         less_charset = "utf-8";
 161                 if (less_charset &&
 162                     setenv("LESSCHARSET", less_charset, 1) < 0) {
 163                         log_error_errno(errno, "Failed to set environment variable LESSCHARSET: %m");
 164                         _exit(EXIT_FAILURE);
 165                 }
 166
 167                 if (pager_args) {
 168                         r = loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1, false);
 169                         if (r < 0) {
 170                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 171                                 _exit(EXIT_FAILURE);
 172                         }
 173
 174                         execvp(pager_args[0], pager_args);
 175                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 176                                        "Failed to execute '%s', using fallback pagers: %m", pager_args[0]);
 177                 }
 178
 179                 /* Debian's alternatives command for pagers is
 180                  * called 'pager'. Note that we do not call
 181                  * sensible-pagers here, since that is just a
 182                  * shell script that implements a logic that
 183                  * is similar to this one anyway, but is
 184                  * Debian-specific. */
 185                 FOREACH_STRING(exe, "pager", "less", "more") {
 186                         r = loop_write(exe_name_pipe[1], exe, strlen(exe) + 1, false);
 187                         if (r  < 0) {
 188                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 189                                 _exit(EXIT_FAILURE);
 190                         }
 191                         execlp(exe, exe, NULL);
 192                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 193                                        "Failed to execute '%s', using next fallback pager: %m", exe);
 194                 }
 195
 196                 r = loop_write(exe_name_pipe[1], "(built-in)", strlen("(built-in)") + 1, false);
 197                 if (r < 0) {
 198                         log_error_errno(r, "Failed to write pager name to socket: %m");
 199                         _exit(EXIT_FAILURE);
 200                 }
 201                 /* Close pipe to signal the parent to start sending data */
 202                 safe_close_pair(exe_name_pipe);
 203                 pager_fallback();
 204                 /* not reached */
 205         }
 206
 207         /* Return in the parent */
 208         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 209         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 210                 stored_stdout = safe_close(stored_stdout);
 211                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 212         }
 213         stdout_redirected = true;
 214
 215         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 216         if (dup2(fd[1], STDERR_FILENO) < 0) {
 217                 stored_stderr = safe_close(stored_stderr);
 218                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 219         }
 220         stderr_redirected = true;
 221
 222         exe_name_pipe[1] = safe_close(exe_name_pipe[1]);
 223
 224         r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts);
 225         if (r < 0)
 226                 return r;
 227         if (r > 0)
 228                 (void) ignore_signals(SIGINT, -1);
 229
 230         return 1;
 231 }
 232
 233 void pager_close(void) {
 234
 235         if (pager_pid <= 0)
 236                 return;
 237
 238         /* Inform pager that we are done */
 239         (void) fflush(stdout);
 240         if (stdout_redirected)
 241                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 242                         (void) close(STDOUT_FILENO);
 243         stored_stdout = safe_close(stored_stdout);
 244         (void) fflush(stderr);
 245         if (stderr_redirected)
 246                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 247                         (void) close(STDERR_FILENO);
 248         stored_stderr = safe_close(stored_stderr);
 249         stdout_redirected = stderr_redirected = false;
 250
 251         (void) kill(pager_pid, SIGCONT);
 252         (void) wait_for_terminate(pager_pid, NULL);
 253         pager_pid = 0;
 254 }
 255
 256 bool pager_have(void) {
 257         return pager_pid > 0;
 258 }
 259
 260 int show_man_page(const char *desc, bool null_stdio) {
 261         const char *args[4] = { "man", NULL, NULL, NULL };
 262         char *e = NULL;
 263         pid_t pid;
 264         size_t k;
 265         int r;
 266
 267         k = strlen(desc);
 268
 269         if (desc[k-1] == ')')
 270                 e = strrchr(desc, '(');
 271
 272         if (e) {
 273                 char *page = NULL, *section = NULL;
 274
 275                 page = strndupa(desc, e - desc);
 276                 section = strndupa(e + 1, desc + k - e - 2);
 277
 278                 args[1] = section;
 279                 args[2] = page;
 280         } else
 281                 args[1] = desc;
 282
 283         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG|(null_stdio ? FORK_NULL_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
 284         if (r < 0)
 285                 return r;
 286         if (r == 0) {
 287                 /* Child */
 288                 execvp(args[0], (char**) args);
 289                 log_error_errno(errno, "Failed to execute man: %m");
 290                 _exit(EXIT_FAILURE);
 291         }
 292
 293         return wait_for_terminate_and_check(NULL, pid, 0);
 294 }