glue/inotify-glue.c

   1 /*
   2  * inotify-glue.c
   3  *
   4  * Copyright (C) 2004 Novell, Inc.
   5  *
   6  */
   7
   8 /*
   9  * Permission is hereby granted, free of charge, to any person obtaining a
  10  * copy of this software and associated documentation files (the "Software"),
  11  * to deal in the Software without restriction, including without limitation
  12  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  13  * and/or sell copies of the Software, and to permit persons to whom the
  14  * Software is furnished to do so, subject to the following conditions:
  15  *
  16  * The above copyright notice and this permission notice shall be included in
  17  * all copies or substantial portions of the Software.
  18  *
  19  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  22  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  23  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  24  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  25  * DEALINGS IN THE SOFTWARE.
  26  */
  27
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31 #include <fcntl.h>
  32 #include <unistd.h>
  33 #include <errno.h>
  34 #include <sys/ioctl.h>
  35 #include <sys/select.h>
  36 #include <sys/types.h>
  37
  38 #include "inotify.h"
  39 #include "inotify-syscalls.h"
  40
  41 #define PROCFS_PREFIX           "/proc/sys/fs/inotify"
  42
  43 #define PROCFS_MAX_USER_DEVICES  PROCFS_PREFIX "/max_user_instances"
  44 #define PROCFS_MAX_USER_WATCHES  PROCFS_PREFIX "/max_user_watches"
  45 #define PROCFS_MAX_QUEUED_EVENTS PROCFS_PREFIX "/max_queued_events"
  46
  47 /* Inotify sysfs knobs, initialized to their pre-sysfs defaults */
  48 static int max_user_instances = 8;
  49 static int max_user_watches = 8192;
  50 static unsigned int max_queued_events = 256;
  51
  52 /* Paranoid code to read an integer from a sysfs (well, any) file. */
  53 static void
  54 read_int (const char *filename, int *var)
  55 {
  56         int fd, n;
  57         char buffer[32];
  58         char *buffer_endptr = NULL;
  59
  60         fd = open (filename, O_RDONLY);
  61         if (fd == -1)
  62                 return;
  63         if (read (fd, buffer, 31) > 0) {
  64                 n = (int) strtol (buffer, &buffer_endptr, 10);
  65                 if (*buffer != '\0' && *buffer_endptr == '\0')
  66                         *var = n;
  67         }
  68         close (fd);
  69 }
  70
  71
  72 int
  73 inotify_glue_init (void)
  74 {
  75         static int fd = 0;
  76         if (fd)
  77                 return fd;
  78         fd = inotify_init ();
  79         if (fd < 0) {
  80                 int _errno = errno;
  81                 perror ("inotify_init");
  82                 switch (_errno) {
  83                 case ENOSYS:
  84                         fprintf(stderr, "Inotify not supported!  You need a "
  85                                 "2.6.13 kernel or later with CONFIG_INOTIFY "
  86                                 "enabled.");
  87                         break;
  88                 }
  89         }
  90
  91         read_int (PROCFS_MAX_USER_DEVICES, &max_user_instances);
  92         read_int (PROCFS_MAX_USER_WATCHES, &max_user_watches);
  93         read_int (PROCFS_MAX_QUEUED_EVENTS, &max_queued_events);
  94
  95         return fd;
  96 }
  97
  98
  99 int
 100 inotify_glue_watch (int fd, const char *filename, __u32 mask)
 101 {
 102         int wd;
 103
 104         wd = inotify_add_watch (fd, filename, mask);
 105         if (wd < 0) {
 106                 int _errno = errno;
 107                 perror ("inotify_add_watch");
 108                 switch (_errno) {
 109                 case ENOSPC:
 110                         fprintf(stderr, "Maximum watch limit hit. "
 111                                 "Try adjusting " PROCFS_MAX_USER_WATCHES ".\n");
 112                         break;
 113                 }
 114         }
 115
 116         return wd;
 117 }
 118
 119
 120 int
 121 inotify_glue_ignore (int fd, __s32 wd)
 122 {
 123         int ret;
 124
 125         ret = inotify_rm_watch (fd, wd);
 126         if (ret < 0)
 127                 perror ("inotify_rm_watch");
 128
 129         return ret;
 130 }
 131
 132
 133 #define MAX_PENDING_COUNT           5
 134 #define PENDING_PAUSE_MICROSECONDS  2000
 135 #define PENDING_THRESHOLD(qsize)    ((unsigned int) (qsize) >> 1)
 136 #define PENDING_MARGINAL_COST(p)    ((unsigned int) (1 << (p)))
 137
 138 void
 139 inotify_snarf_events (int fd, int timeout_secs, int *nr, void **buffer_out)
 140 {
 141         struct timeval timeout;
 142         fd_set read_fds;
 143         int select_retval;
 144         unsigned int prev_pending = 0, pending_count = 0;
 145         static struct inotify_event *buffer = NULL;
 146         static size_t buffer_size;
 147
 148         /* Allocate our buffer the first time we try to read events. */
 149         if (buffer == NULL) {
 150                 /* guess the avg len */
 151                 buffer_size = sizeof (struct inotify_event) + 16;
 152                 buffer_size *= max_queued_events;
 153                 buffer = malloc (buffer_size);
 154                 if (!buffer) {
 155                         perror ("malloc");
 156                         *buffer_out = NULL;
 157                         return;
 158                 }
 159         }
 160
 161         /* Set nr to 0, so it will be sure to contain something
 162            valid if the select times out. */
 163         *nr = 0;
 164
 165         /* Wait for the file descriptor to be ready to read. */
 166
 167         timeout.tv_sec = timeout_secs;
 168         timeout.tv_usec = 0;
 169
 170         FD_ZERO (&read_fds);
 171         FD_SET (fd, &read_fds);
 172
 173         select_retval = select (fd + 1, &read_fds, NULL, NULL, &timeout);
 174
 175         /* If we time out or get an error, just return */
 176         if (select_retval <= 0)
 177                 return;
 178
 179         /* Reading events in groups significantly helps performance.
 180          * If there are some events (but not too many!) ready, wait a
 181          * bit more to see if more events come in. */
 182
 183         while (pending_count < MAX_PENDING_COUNT) {
 184                 unsigned int pending;
 185
 186                 if (ioctl (fd, FIONREAD, &pending) == -1)
 187                         break;
 188                 pending /= sizeof (struct inotify_event) + 16;  /* guess len */
 189
 190                 /* Don't wait if the number of pending events is too close
 191                  * to the maximum queue size. */
 192                 if (pending > PENDING_THRESHOLD (max_queued_events))
 193                         break;
 194
 195                 /* With each successive iteration, the minimum rate for
 196                  * further sleep doubles. */
 197                 if (pending-prev_pending < PENDING_MARGINAL_COST(pending_count))
 198                         break;
 199
 200                 prev_pending = pending;
 201                 ++pending_count;
 202
 203                 timeout.tv_sec = 0;
 204                 timeout.tv_usec = PENDING_PAUSE_MICROSECONDS;
 205                 select (0, NULL, NULL, NULL, &timeout);
 206         }
 207
 208         *nr = read (fd, buffer, buffer_size);
 209
 210         *buffer_out = buffer;
 211 }