miscutils/inotifyd.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * simple inotify daemon
   4  * reports filesystem changes via userspace agent
   5  *
   6  * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
   7  *
   8  * Licensed under GPLv2, see file LICENSE in this source tree.
   9  */
  10
  11 /*
  12  * Use as follows:
  13  * # inotifyd /user/space/agent dir/or/file/being/watched[:mask] ...
  14  *
  15  * When a filesystem event matching the specified mask is occurred on specified file (or directory)
  16  * a userspace agent is spawned and given the following parameters:
  17  * $1. actual event(s)
  18  * $2. file (or directory) name
  19  * $3. name of subfile (if any), in case of watching a directory
  20  *
  21  * E.g. inotifyd ./dev-watcher /dev:n
  22  *
  23  * ./dev-watcher can be, say:
  24  * #!/bin/sh
  25  * echo "We have new device in here! Hello, $3!"
  26  *
  27  * See below for mask names explanation.
  28  */
  29 //config:config INOTIFYD
  30 //config:       bool "inotifyd (3.6 kb)"
  31 //config:       default n  # doesn't build on Knoppix 5
  32 //config:       help
  33 //config:       Simple inotify daemon. Reports filesystem changes. Requires
  34 //config:       kernel >= 2.6.13
  35
  36 //applet:IF_INOTIFYD(APPLET(inotifyd, BB_DIR_SBIN, BB_SUID_DROP))
  37
  38 //kbuild:lib-$(CONFIG_INOTIFYD) += inotifyd.o
  39
  40 //usage:#define inotifyd_trivial_usage
  41 //usage:        "PROG FILE1[:MASK]..."
  42 //usage:#define inotifyd_full_usage "\n\n"
  43 //usage:       "Run PROG on filesystem changes."
  44 //usage:     "\nWhen a filesystem event matching MASK occurs on FILEn,"
  45 //usage:     "\nPROG ACTUAL_EVENTS FILEn [SUBFILE] is run."
  46 //usage:     "\nIf PROG is -, events are sent to stdout."
  47 //usage:     "\nEvents:"
  48 //usage:     "\n        a       File is accessed"
  49 //usage:     "\n        c       File is modified"
  50 //usage:     "\n        e       Metadata changed"
  51 //usage:     "\n        w       Writable file is closed"
  52 //usage:     "\n        0       Unwritable file is closed"
  53 //usage:     "\n        r       File is opened"
  54 //usage:     "\n        D       File is deleted"
  55 //usage:     "\n        M       File is moved"
  56 //usage:     "\n        u       Backing fs is unmounted"
  57 //usage:     "\n        o       Event queue overflowed"
  58 //usage:     "\n        x       File can't be watched anymore"
  59 //usage:     "\nIf watching a directory:"
  60 //usage:     "\n        y       Subfile is moved into dir"
  61 //usage:     "\n        m       Subfile is moved out of dir"
  62 //usage:     "\n        n       Subfile is created"
  63 //usage:     "\n        d       Subfile is deleted"
  64 //usage:     "\n"
  65 //usage:     "\ninotifyd waits for PROG to exit."
  66 //usage:     "\nWhen x event happens for all FILEs, inotifyd exits."
  67
  68 #include "libbb.h"
  69 #include "common_bufsiz.h"
  70 #include <sys/inotify.h>
  71
  72 static const char mask_names[] ALIGN1 =
  73         "a"     // 0x00000001   File was accessed
  74         "c"     // 0x00000002   File was modified
  75         "e"     // 0x00000004   Metadata changed
  76         "w"     // 0x00000008   Writable file was closed
  77         "0"     // 0x00000010   Unwritable file closed
  78         "r"     // 0x00000020   File was opened
  79         "m"     // 0x00000040   File was moved from X
  80         "y"     // 0x00000080   File was moved to Y
  81         "n"     // 0x00000100   Subfile was created
  82         "d"     // 0x00000200   Subfile was deleted
  83         "D"     // 0x00000400   Self was deleted
  84         "M"     // 0x00000800   Self was moved
  85         "\0"    // 0x00001000   (unused)
  86         // Kernel events, always reported:
  87         "u"     // 0x00002000   Backing fs was unmounted
  88         "o"     // 0x00004000   Event queued overflowed
  89         "x"     // 0x00008000   File is no longer watched (usually deleted)
  90 ;
  91 enum {
  92         MASK_BITS = sizeof(mask_names) - 1
  93 };
  94
  95 int inotifyd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  96 int inotifyd_main(int argc, char **argv)
  97 {
  98         int n;
  99         unsigned mask;
 100         struct pollfd pfd;
 101         char **watches; // names of files being watched
 102         const char *args[5];
 103
 104         // sanity check: agent and at least one watch must be given
 105         if (!argv[1] || !argv[2])
 106                 bb_show_usage();
 107
 108         argv++;
 109         // inotify_add_watch will number watched files
 110         // starting from 1, thus watches[0] is unimportant,
 111         // and 1st file name is watches[1].
 112         watches = argv;
 113         args[0] = *argv;
 114         args[4] = NULL;
 115         argc -= 2; // number of files we watch
 116
 117         // open inotify
 118         pfd.fd = inotify_init();
 119         if (pfd.fd < 0)
 120                 bb_simple_perror_msg_and_die("no kernel support");
 121
 122         // setup watches
 123         while (*++argv) {
 124                 char *path = *argv;
 125                 char *masks = strchr(path, ':');
 126
 127                 mask = 0x0fff; // assuming we want all non-kernel events
 128                 // if mask is specified ->
 129                 if (masks) {
 130                         *masks = '\0'; // split path and mask
 131                         // convert mask names to mask bitset
 132                         mask = 0;
 133                         while (*++masks) {
 134                                 const char *found;
 135                                 found = memchr(mask_names, *masks, MASK_BITS);
 136                                 if (found)
 137                                         mask |= (1 << (found - mask_names));
 138                         }
 139                 }
 140                 // add watch
 141                 n = inotify_add_watch(pfd.fd, path, mask);
 142                 if (n < 0)
 143                         bb_perror_msg_and_die("add watch (%s) failed", path);
 144                 //bb_error_msg("added %d [%s]:%4X", n, path, mask);
 145         }
 146
 147         // setup signals
 148         bb_signals(BB_FATAL_SIGS, record_signo);
 149
 150         // do watch
 151         pfd.events = POLLIN;
 152         while (1) {
 153                 int len;
 154                 void *buf;
 155                 struct inotify_event *ie;
 156  again:
 157                 if (bb_got_signal)
 158                         break;
 159                 n = poll(&pfd, 1, -1);
 160                 // Signal interrupted us?
 161                 if (n < 0 && errno == EINTR)
 162                         goto again;
 163                 // Under Linux, above if() is not necessary.
 164                 // Non-fatal signals, e.g. SIGCHLD, when set to SIG_DFL,
 165                 // are not interrupting poll().
 166                 // Thus we can just break if n <= 0 (see below),
 167                 // because EINTR will happen only on SIGTERM et al.
 168                 // But this might be not true under other Unixes,
 169                 // and is generally way too subtle to depend on.
 170                 if (n <= 0) // strange error?
 171                         break;
 172
 173                 // read out all pending events
 174                 // (NB: len must be int, not ssize_t or long!)
 175 #define eventbuf bb_common_bufsiz1
 176                 setup_common_bufsiz();
 177                 xioctl(pfd.fd, FIONREAD, &len);
 178                 ie = buf = (len <= COMMON_BUFSIZE) ? eventbuf : xmalloc(len);
 179                 len = full_read(pfd.fd, buf, len);
 180                 // process events. N.B. events may vary in length
 181                 while (len > 0) {
 182                         int i;
 183                         // cache relevant events mask
 184                         unsigned m = ie->mask & ((1 << MASK_BITS) - 1);
 185                         if (m) {
 186                                 char events[MASK_BITS + 1];
 187                                 char *s = events;
 188                                 for (i = 0; i < MASK_BITS; ++i, m >>= 1) {
 189                                         if ((m & 1) && (mask_names[i] != '\0'))
 190                                                 *s++ = mask_names[i];
 191                                 }
 192                                 *s = '\0';
 193                                 if (LONE_CHAR(args[0], '-')) {
 194                                         /* "inotifyd - FILE": built-in echo */
 195                                         printf(ie->len ? "%s\t%s\t%s\n" : "%s\t%s\n", events,
 196                                                         watches[ie->wd],
 197                                                         ie->name);
 198                                         fflush(stdout);
 199                                 } else {
 200 //                                      bb_error_msg("exec %s %08X\t%s\t%s\t%s", args[0],
 201 //                                              ie->mask, events, watches[ie->wd], ie->len ? ie->name : "");
 202                                         args[1] = events;
 203                                         args[2] = watches[ie->wd];
 204                                         args[3] = ie->len ? ie->name : NULL;
 205                                         spawn_and_wait((char **)args);
 206                                 }
 207                                 // we are done if all files got final x event
 208                                 if (ie->mask & 0x8000) {
 209                                         if (--argc <= 0)
 210                                                 goto done;
 211                                         inotify_rm_watch(pfd.fd, ie->wd);
 212                                 }
 213                         }
 214                         // next event
 215                         i = sizeof(struct inotify_event) + ie->len;
 216                         len -= i;
 217                         ie = (void*)((char*)ie + i);
 218                 }
 219                 if (eventbuf != buf)
 220                         free(buf);
 221         } // while (1)
 222  done:
 223         return bb_got_signal;
 224 }