glue/inotify-glue.c

   1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*- */
   2
   3 /*
   4  * inotify-glue.c
   5  *
   6  * Copyright (C) 2004 Novell, Inc.
   7  *
   8  */
   9
  10 /*
  11  * Permission is hereby granted, free of charge, to any person obtaining a
  12  * copy of this software and associated documentation files (the "Software"),
  13  * to deal in the Software without restriction, including without limitation
  14  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  15  * and/or sell copies of the Software, and to permit persons to whom the
  16  * Software is furnished to do so, subject to the following conditions:
  17  *
  18  * The above copyright notice and this permission notice shall be included in
  19  * all copies or substantial portions of the Software.
  20  *
  21  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  22  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  23  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  24  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  25  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  26  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  27  * DEALINGS IN THE SOFTWARE.
  28  */
  29
  30 #include <stdio.h>
  31 #include <stdlib.h>
  32 #include <fcntl.h>
  33 #include <time.h>
  34 #include <unistd.h>
  35 #include <errno.h>
  36 #include <sys/ioctl.h>
  37 #include <sys/poll.h>
  38 #include <sys/types.h>
  39
  40 #include "inotify.h"
  41 #include "inotify-syscalls.h"
  42
  43 #define PROCFS_PREFIX           "/proc/sys/fs/inotify"
  44
  45 #define PROCFS_MAX_USER_DEVICES  PROCFS_PREFIX "/max_user_instances"
  46 #define PROCFS_MAX_USER_WATCHES  PROCFS_PREFIX "/max_user_watches"
  47 #define PROCFS_MAX_QUEUED_EVENTS PROCFS_PREFIX "/max_queued_events"
  48
  49 /* Inotify sysfs knobs, initialized to their pre-sysfs defaults */
  50 static int max_user_instances = 8;
  51 static int max_user_watches = 8192;
  52 static int max_queued_events = 256;
  53
  54 static int snarf_cancellation_pipe [2];
  55
  56 /* Paranoid code to read an integer from a sysfs (well, any) file. */
  57 static void
  58 read_int (const char *filename, int *var)
  59 {
  60         int fd, n;
  61         char buffer[32];
  62         char *buffer_endptr = NULL;
  63
  64         fd = open (filename, O_RDONLY);
  65         if (fd == -1)
  66                 return;
  67         if (read (fd, buffer, 31) > 0) {
  68                 n = (int) strtol (buffer, &buffer_endptr, 10);
  69                 if (*buffer != '\0' && *buffer_endptr == '\0')
  70                         *var = n;
  71         }
  72         close (fd);
  73 }
  74
  75
  76 int
  77 inotify_glue_init (void)
  78 {
  79         static int fd = 0;
  80
  81         if (fd)
  82                 return fd;
  83
  84         fd = inotify_init ();
  85         if (fd < 0) {
  86                 int err = errno;
  87                 perror ("inotify_init");
  88                 if (err == ENOSYS)
  89                         fprintf(stderr, "Inotify not supported!  You need a "
  90                                 "2.6.13 kernel or later with CONFIG_INOTIFY "
  91                                 "enabled.");
  92         }
  93
  94         if (pipe (snarf_cancellation_pipe) == -1)
  95                 perror ("Can't create snarf_cancellation_pipe");
  96
  97         read_int (PROCFS_MAX_USER_DEVICES, &max_user_instances);
  98         read_int (PROCFS_MAX_USER_WATCHES, &max_user_watches);
  99         read_int (PROCFS_MAX_QUEUED_EVENTS, &max_queued_events);
 100
 101         return fd;
 102 }
 103
 104
 105 int
 106 inotify_glue_watch (int fd, const char *filename, __u32 mask)
 107 {
 108         int wd;
 109
 110         wd = inotify_add_watch (fd, filename, mask);
 111         if (wd < 0) {
 112                 int err = errno;
 113                 perror ("inotify_add_watch");
 114                 if (err == ENOSPC)
 115                         fprintf(stderr, "Maximum watch limit hit. "
 116                                 "Try adjusting " PROCFS_MAX_USER_WATCHES ".\n");
 117         }
 118
 119         return wd;
 120 }
 121
 122
 123 int
 124 inotify_glue_ignore (int fd, __u32 wd)
 125 {
 126         int ret;
 127
 128         ret = inotify_rm_watch (fd, wd);
 129         if (ret < 0)
 130                 perror ("inotify_rm_watch");
 131
 132         return ret;
 133 }
 134
 135 void
 136 inotify_snarf_cancel ()
 137 {
 138         write (snarf_cancellation_pipe [1],
 139                &snarf_cancellation_pipe, 1); // write a convenient byte
 140 }
 141
 142
 143 #define MAX_PENDING_COUNT               5
 144 #define PENDING_PAUSE_NANOSECONDS       2000000
 145 #define PENDING_THRESHOLD(qsize)        ((unsigned int) (qsize) >> 1)
 146 #define PENDING_MARGINAL_COST(p)        ((unsigned int) (1 << (p)))
 147
 148 void
 149 inotify_snarf_events (int fd, int *nr, void **buffer_out)
 150 {
 151         struct pollfd pollfd [2]  = { { fd, POLLIN | POLLPRI, 0 }, { snarf_cancellation_pipe [0], POLLIN, 0} };
 152         unsigned int prev_pending = 0, pending_count = 0;
 153         static struct inotify_event *buffer = NULL;
 154         static size_t buffer_size;
 155         int ret;
 156
 157         /* Allocate our buffer the first time we try to read events. */
 158         if (buffer == NULL) {
 159                 /* guess the avg len */
 160                 buffer_size = sizeof (struct inotify_event) + 16;
 161                 buffer_size *= max_queued_events;
 162                 buffer = malloc (buffer_size);
 163                 if (!buffer) {
 164                         perror ("malloc");
 165                         *buffer_out = NULL;
 166                         return;
 167                 }
 168         }
 169
 170         /* Set nr to 0, so it will be sure to contain something
 171            valid if the poll times out. */
 172         *nr = 0;
 173
 174         /* Wait for the file descriptor to be ready to read. */
 175         ret = poll (pollfd, 2, -1);
 176         if (ret == -1) {
 177                 if (errno != EINTR)
 178                         perror ("poll");
 179                 return;
 180         } else if (ret == 0)
 181                 return;
 182
 183         /* Return immediately if something happened on the
 184            snarf cancellation pipe. */
 185         if (pollfd [1].revents != 0)
 186                 return;
 187
 188         /* Reading events in groups significantly helps performance.
 189          * If there are some events (but not too many!) ready, wait a
 190          * bit more to see if more events come in. */
 191
 192         while (pending_count < MAX_PENDING_COUNT) {
 193                 struct timespec ts = {0, PENDING_PAUSE_NANOSECONDS};
 194                 unsigned int pending;
 195
 196                 if (ioctl (fd, FIONREAD, &pending) == -1)
 197                         break;
 198
 199                 /* Don't wait if the number of pending events is too close
 200                  * to the maximum queue size. */
 201                 pending /= sizeof (struct inotify_event) + 16;
 202                 if (pending > PENDING_THRESHOLD (max_queued_events))
 203                         break;
 204
 205                 /* With each successive iteration, the minimum rate for
 206                  * further sleep doubles. */
 207                 if (pending-prev_pending < PENDING_MARGINAL_COST(pending_count))
 208                         break;
 209
 210                 prev_pending = pending;
 211                 ++pending_count;
 212
 213                 nanosleep (&ts, NULL);
 214         }
 215
 216         *nr = read (fd, buffer, buffer_size);
 217
 218         *buffer_out = buffer;
 219 }