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_error_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 log_error_errno(r, "Failed to read from socket: %m");
  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 log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread.");
 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 log_oom();
 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_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                 pager_fallback();
 202                 /* not reached */
 203         }
 204
 205         /* Return in the parent */
 206         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 207         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 208                 stored_stdout = safe_close(stored_stdout);
 209                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 210         }
 211         stdout_redirected = true;
 212
 213         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 214         if (dup2(fd[1], STDERR_FILENO) < 0) {
 215                 stored_stderr = safe_close(stored_stderr);
 216                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 217         }
 218         stderr_redirected = true;
 219
 220         exe_name_pipe[1] = safe_close(exe_name_pipe[1]);
 221
 222         r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts);
 223         if (r < 0)
 224                 return r;
 225         if (r > 0)
 226                 (void) ignore_signals(SIGINT, -1);
 227
 228         return 1;
 229 }
 230
 231 void pager_close(void) {
 232
 233         if (pager_pid <= 0)
 234                 return;
 235
 236         /* Inform pager that we are done */
 237         (void) fflush(stdout);
 238         if (stdout_redirected)
 239                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 240                         (void) close(STDOUT_FILENO);
 241         stored_stdout = safe_close(stored_stdout);
 242         (void) fflush(stderr);
 243         if (stderr_redirected)
 244                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 245                         (void) close(STDERR_FILENO);
 246         stored_stderr = safe_close(stored_stderr);
 247         stdout_redirected = stderr_redirected = false;
 248
 249         (void) kill(pager_pid, SIGCONT);
 250         (void) wait_for_terminate(pager_pid, NULL);
 251         pager_pid = 0;
 252 }
 253
 254 bool pager_have(void) {
 255         return pager_pid > 0;
 256 }
 257
 258 int show_man_page(const char *desc, bool null_stdio) {
 259         const char *args[4] = { "man", NULL, NULL, NULL };
 260         char *e = NULL;
 261         pid_t pid;
 262         size_t k;
 263         int r;
 264
 265         k = strlen(desc);
 266
 267         if (desc[k-1] == ')')
 268                 e = strrchr(desc, '(');
 269
 270         if (e) {
 271                 char *page = NULL, *section = NULL;
 272
 273                 page = strndupa(desc, e - desc);
 274                 section = strndupa(e + 1, desc + k - e - 2);
 275
 276                 args[1] = section;
 277                 args[2] = page;
 278         } else
 279                 args[1] = desc;
 280
 281         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG|(null_stdio ? FORK_NULL_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
 282         if (r < 0)
 283                 return r;
 284         if (r == 0) {
 285                 /* Child */
 286                 execvp(args[0], (char**) args);
 287                 log_error_errno(errno, "Failed to execute man: %m");
 288                 _exit(EXIT_FAILURE);
 289         }
 290
 291         return wait_for_terminate_and_check(NULL, pid, 0);
 292 }