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inotify-glue.c

/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*- */

/*
 * inotify-glue.c
 *
 * Copyright (C) 2004 Novell, Inc.
 *
 */

/*
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/poll.h>
#include <sys/types.h>

#include "inotify.h"
#include "inotify-syscalls.h"

#define PROCFS_PREFIX           "/proc/sys/fs/inotify"

#define PROCFS_MAX_USER_DEVICES  PROCFS_PREFIX "/max_user_instances"
#define PROCFS_MAX_USER_WATCHES  PROCFS_PREFIX "/max_user_watches"
#define PROCFS_MAX_QUEUED_EVENTS PROCFS_PREFIX "/max_queued_events"

/* Inotify sysfs knobs, initialized to their pre-sysfs defaults */
static int max_user_instances = 8;
static int max_user_watches = 8192;
static int max_queued_events = 256;

static int snarf_cancellation_pipe [2];

/* Paranoid code to read an integer from a sysfs (well, any) file. */
static void
read_int (const char *filename, int *var)
{
    int fd, n;
    char buffer[32];
    char *buffer_endptr = NULL;

    fd = open (filename, O_RDONLY);
    if (fd == -1)
        return;
    if (read (fd, buffer, 31) > 0) {
        n = (int) strtol (buffer, &buffer_endptr, 10);
        if (*buffer != '\0' && *buffer_endptr == '\0')
            *var = n;
    }
    close (fd);
}


int
inotify_glue_init (void)
{
    static int fd = 0;

    if (fd)
        return fd;

    fd = inotify_init ();
    if (fd < 0) {
        int err = errno;
        perror ("inotify_init");
        if (err == ENOSYS)
            fprintf(stderr, "Inotify not supported!  You need a "
                "2.6.13 kernel or later with CONFIG_INOTIFY "
                "enabled.");
        return -1;
    }

    if (pipe (snarf_cancellation_pipe) == -1)
        perror ("Can't create snarf_cancellation_pipe");
    
    read_int (PROCFS_MAX_USER_DEVICES, &max_user_instances);
    read_int (PROCFS_MAX_USER_WATCHES, &max_user_watches);
    read_int (PROCFS_MAX_QUEUED_EVENTS, &max_queued_events);

    return fd;
}


int
inotify_glue_watch (int fd, const char *filename, __u32 mask)
{
    int wd;

    wd = inotify_add_watch (fd, filename, mask);
    if (wd < 0) {
        int err = errno;
        perror ("inotify_add_watch");
        if (err == ENOSPC)
            fprintf(stderr, "Maximum watch limit hit. "
                "Try adjusting " PROCFS_MAX_USER_WATCHES ".\n");
    }

    return wd;
}


int
inotify_glue_ignore (int fd, __u32 wd)
{
    int ret;

    ret = inotify_rm_watch (fd, wd);
    if (ret < 0)
        perror ("inotify_rm_watch");

    return ret;
}

void
inotify_snarf_cancel ()
{
    write (snarf_cancellation_pipe [1],
           &snarf_cancellation_pipe, 1); // write a convenient byte
}


#define MAX_PENDING_COUNT        5
#define PENDING_PAUSE_NANOSECONDS    2000000
#define PENDING_THRESHOLD(qsize)    ((unsigned int) (qsize) >> 1)
#define PENDING_MARGINAL_COST(p)    ((unsigned int) (1 << (p)))

void
inotify_snarf_events (int fd, int *nr, void **buffer_out)
{
    struct pollfd pollfd [2]  = { { fd, POLLIN | POLLPRI, 0 }, { snarf_cancellation_pipe [0], POLLIN, 0} };
    unsigned int prev_pending = 0, pending_count = 0;
    static struct inotify_event *buffer = NULL;
    static size_t buffer_size;
    int ret;

    /* Allocate our buffer the first time we try to read events. */
    if (buffer == NULL) {
        /* guess the avg len */
        buffer_size = sizeof (struct inotify_event) + 16;
        buffer_size *= max_queued_events;
        buffer = malloc (buffer_size);
        if (!buffer) {
            perror ("malloc");
            *buffer_out = NULL;
            return;
        }
    }

    /* Set nr to 0, so it will be sure to contain something
       valid if the poll times out. */
    *nr = 0;

    /* Wait for the file descriptor to be ready to read. */
    ret = poll (pollfd, 2, -1);
    if (ret == -1) {
        if (errno != EINTR)
            perror ("poll");
        return;
    } else if (ret == 0)
        return;

    /* Return immediately if something happened on the
       snarf cancellation pipe. */
    if (pollfd [1].revents != 0)
        return;

    /* Reading events in groups significantly helps performance.
     * If there are some events (but not too many!) ready, wait a
     * bit more to see if more events come in. */

    while (pending_count < MAX_PENDING_COUNT) {
        struct timespec ts = {0, PENDING_PAUSE_NANOSECONDS};
        unsigned int pending;

        if (ioctl (fd, FIONREAD, &pending) == -1)
            break;

        /* Don't wait if the number of pending events is too close
         * to the maximum queue size. */
        pending /= sizeof (struct inotify_event) + 16;        
        if (pending > PENDING_THRESHOLD (max_queued_events))
            break;

        /* With each successive iteration, the minimum rate for
         * further sleep doubles. */
        if (pending-prev_pending < PENDING_MARGINAL_COST(pending_count))
            break;

        prev_pending = pending;
        ++pending_count;

        nanosleep (&ts, NULL);
    }

    *nr = read (fd, buffer, buffer_size);

    *buffer_out = buffer;
}

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