/* vi: set sw=4 ts=4: */
/*
 * simple inotify daemon
 * reports filesystem changes via userspace agent
 *
 * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
 *
 * Licensed under GPLv2, see file LICENSE in this tarball for details.
 */

/*
 * Use as follows:
 * # inotifyd /user/space/agent dir/or/file/being/watched[:mask] ...
 *
 * When a filesystem event matching the specified mask is occured on specified file (or directory)
 * a userspace agent is spawned and given the following parameters:
 * $1. actual event(s)
 * $2. file (or directory) name
 * $3. name of subfile (if any), in case of watching a directory
 *
 * E.g. inotifyd ./dev-watcher /dev:n
 *
 * ./dev-watcher can be, say:
 * #!/bin/sh
 * echo "We have new device in here! Hello, $3!"
 *
 * See below for mask names explanation.
 */

#include "libbb.h"
#include <sys/inotify.h>

static const char mask_names[] ALIGN1 =
        "a"     // 0x00000001   File was accessed
        "c"     // 0x00000002   File was modified
        "e"     // 0x00000004   Metadata changed
        "w"     // 0x00000008   Writtable file was closed
        "0"     // 0x00000010   Unwrittable file closed
        "r"     // 0x00000020   File was opened
        "m"     // 0x00000040   File was moved from X
        "y"     // 0x00000080   File was moved to Y
        "n"     // 0x00000100   Subfile was created
        "d"     // 0x00000200   Subfile was deleted
        "D"     // 0x00000400   Self was deleted
        "M"     // 0x00000800   Self was moved
        "\0"    // 0x00001000   (unused)
        // Kernel events, always reported:
        "u"     // 0x00002000   Backing fs was unmounted
        "o"     // 0x00004000   Event queued overflowed
        "x"     // 0x00008000   File is no longer watched (usually deleted)
;
enum {
        MASK_BITS = sizeof(mask_names) - 1
};

int inotifyd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int inotifyd_main(int argc, char **argv)
{
        int n;
        unsigned mask;
        struct pollfd pfd;
        char **watches; // names of files being watched
        const char *args[5];

        // sanity check: agent and at least one watch must be given
        if (!argv[1] || !argv[2])
                bb_show_usage();

        argv++;
        // inotify_add_watch will number watched files
        // starting from 1, thus watches[0] is unimportant,
        // and 1st file name is watches[1].
        watches = argv;
        args[0] = *argv;
        args[4] = NULL;
        argc -= 2; // number of files we watch

        // open inotify
        pfd.fd = inotify_init();
        if (pfd.fd < 0)
                bb_perror_msg_and_die("no kernel support");

        // setup watches
        while (*++argv) {
                char *path = *argv;
                char *masks = strchr(path, ':');

                mask = 0x0fff; // assuming we want all non-kernel events
                // if mask is specified ->
                if (masks) {
                        *masks = '\0'; // split path and mask
                        // convert mask names to mask bitset
                        mask = 0;
                        while (*++masks) {
                                const char *found;
                                found = memchr(mask_names, *masks, MASK_BITS);
                                if (found)
                                        mask |= (1 << (found - mask_names));
                        }
                }
                // add watch
                n = inotify_add_watch(pfd.fd, path, mask);
                if (n < 0)
                        bb_perror_msg_and_die("add watch (%s) failed", path);
                //bb_error_msg("added %d [%s]:%4X", n, path, mask);
        }

        // setup signals
        bb_signals(BB_FATAL_SIGS, record_signo);

        // do watch
        pfd.events = POLLIN;
        while (1) {
                int len;
                void *buf;
                struct inotify_event *ie;
 again:
                if (bb_got_signal)
                        break;
                n = poll(&pfd, 1, -1);
                // Signal interrupted us?
                if (n < 0 && errno == EINTR)
                        goto again;
                // Under Linux, above if() is not necessary.
                // Non-fatal signals, e.g. SIGCHLD, when set to SIG_DFL,
                // are not interrupting poll().
                // Thus we can just break if n <= 0 (see below),
                // because EINTR will happen only on SIGTERM et al.
                // But this might be not true under other Unixes,
                // and is generally way too subtle to depend on.
                if (n <= 0) // strange error?
                        break;

                // read out all pending events
                // (NB: len must be int, not ssize_t or long!)
                xioctl(pfd.fd, FIONREAD, &len);
#define eventbuf bb_common_bufsiz1
                ie = buf = (len <= sizeof(eventbuf)) ? eventbuf : xmalloc(len);
                len = full_read(pfd.fd, buf, len);
                // process events. N.B. events may vary in length
                while (len > 0) {
                        int i;
                        // cache relevant events mask
                        unsigned m = ie->mask & ((1 << MASK_BITS) - 1);
                        if (m) {
                                char events[MASK_BITS + 1];
                                char *s = events;
                                for (i = 0; i < MASK_BITS; ++i, m >>= 1) {
                                        if ((m & 1) && (mask_names[i] != '\0'))
                                                *s++ = mask_names[i];
                                }
                                *s = '\0';
//                              bb_error_msg("exec %s %08X\t%s\t%s\t%s", args[0],
//                                      ie->mask, events, watches[ie->wd], ie->len ? ie->name : "");
                                args[1] = events;
                                args[2] = watches[ie->wd];
                                args[3] = ie->len ? ie->name : NULL;
                                wait4pid(xspawn((char **)args));
                                // we are done if all files got final x event
                                if (ie->mask & 0x8000) {
                                        if (--argc <= 0)
                                                goto done;
                                        inotify_rm_watch(pfd.fd, ie->wd);
                                }
                        }
                        // next event
                        i = sizeof(struct inotify_event) + ie->len;
                        len -= i;
                        ie = (void*)((char*)ie + i);
                }
                if (eventbuf != buf)
                        free(buf);
        } // while (1)
 done:
        return bb_got_signal;
}