src/common/compat/compat-epoll.c

   1 /*
   2  * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
   3  *
   4  * SPDX-License-Identifier: GPL-2.0-only
   5  *
   6  */
   7
   8 #define _LGPL_SOURCE
   9 #include <assert.h>
  10 #include <fcntl.h>
  11 #include <limits.h>
  12 #include <stdlib.h>
  13 #include <sys/types.h>
  14 #include <sys/stat.h>
  15 #include <unistd.h>
  16 #include <stdbool.h>
  17
  18 #include <common/error.h>
  19 #include <common/defaults.h>
  20 #include <common/macros.h>
  21 #include <common/utils.h>
  22
  23 #include "poll.h"
  24
  25 /*
  26  * Maximum number of fd we can monitor.
  27  *
  28  * For epoll(7), /proc/sys/fs/epoll/max_user_watches (since Linux 2.6.28) will
  29  * be used for the maximum size of the poll set. If this interface is not
  30  * available, according to the manpage, the max_user_watches value is 1/25 (4%)
  31  * of the available low memory divided by the registration cost in bytes which
  32  * is 90 bytes on a 32-bit kernel and 160 bytes on a 64-bit kernel.
  33  *
  34  */
  35 static unsigned int poll_max_size;
  36
  37 /*
  38  * Resize the epoll events structure of the new size.
  39  *
  40  * Return 0 on success or else -1 with the current events pointer untouched.
  41  */
  42 static int resize_poll_event(struct lttng_poll_event *events,
  43                 uint32_t new_size)
  44 {
  45         struct epoll_event *ptr;
  46
  47         assert(events);
  48
  49         ptr = realloc(events->events, new_size * sizeof(*ptr));
  50         if (ptr == NULL) {
  51                 PERROR("realloc epoll add");
  52                 goto error;
  53         }
  54         if (new_size > events->alloc_size) {
  55                 /* Zero newly allocated memory */
  56                 memset(ptr + events->alloc_size, 0,
  57                         (new_size - events->alloc_size) * sizeof(*ptr));
  58         }
  59         events->events = ptr;
  60         events->alloc_size = new_size;
  61
  62         return 0;
  63
  64 error:
  65         return -1;
  66 }
  67
  68 /*
  69  * Create epoll set and allocate returned events structure.
  70  */
  71 LTTNG_HIDDEN
  72 int compat_epoll_create(struct lttng_poll_event *events, int size, int flags)
  73 {
  74         int ret;
  75
  76         if (events == NULL || size <= 0) {
  77                 goto error;
  78         }
  79
  80         if (!poll_max_size) {
  81                 if (lttng_poll_set_max_size()) {
  82                         goto error;
  83                 }
  84         }
  85
  86         /* Don't bust the limit here */
  87         if (size > poll_max_size) {
  88                 size = poll_max_size;
  89         }
  90
  91         ret = compat_glibc_epoll_create(size, flags);
  92         if (ret < 0) {
  93                 /* At this point, every error is fatal */
  94                 PERROR("epoll_create1");
  95                 goto error;
  96         }
  97
  98         events->epfd = ret;
  99
 100         /* This *must* be freed by using lttng_poll_free() */
 101         events->events = zmalloc(size * sizeof(struct epoll_event));
 102         if (events->events == NULL) {
 103                 PERROR("zmalloc epoll set");
 104                 goto error_close;
 105         }
 106
 107         events->alloc_size = events->init_size = size;
 108         events->nb_fd = 0;
 109
 110         return 0;
 111
 112 error_close:
 113         ret = close(events->epfd);
 114         if (ret) {
 115                 PERROR("close");
 116         }
 117 error:
 118         return -1;
 119 }
 120
 121 /*
 122  * Add a fd to the epoll set with requesting events.
 123  */
 124 LTTNG_HIDDEN
 125 int compat_epoll_add(struct lttng_poll_event *events, int fd, uint32_t req_events)
 126 {
 127         int ret;
 128         struct epoll_event ev;
 129
 130         if (events == NULL || events->events == NULL || fd < 0) {
 131                 ERR("Bad compat epoll add arguments");
 132                 goto error;
 133         }
 134
 135         /*
 136          * Zero struct epoll_event to ensure all representations of its
 137          * union are zeroed.
 138          */
 139         memset(&ev, 0, sizeof(ev));
 140         ev.events = req_events;
 141         ev.data.fd = fd;
 142
 143         ret = epoll_ctl(events->epfd, EPOLL_CTL_ADD, fd, &ev);
 144         if (ret < 0) {
 145                 switch (errno) {
 146                 case EEXIST:
 147                         /* If exist, it's OK. */
 148                         goto end;
 149                 case ENOSPC:
 150                 case EPERM:
 151                         /* Print PERROR and goto end not failing. Show must go on. */
 152                         PERROR("epoll_ctl ADD");
 153                         goto end;
 154                 default:
 155                         PERROR("epoll_ctl ADD fatal");
 156                         goto error;
 157                 }
 158         }
 159
 160         events->nb_fd++;
 161
 162 end:
 163         return 0;
 164
 165 error:
 166         return -1;
 167 }
 168
 169 /*
 170  * Remove a fd from the epoll set.
 171  */
 172 LTTNG_HIDDEN
 173 int compat_epoll_del(struct lttng_poll_event *events, int fd)
 174 {
 175         int ret;
 176
 177         if (events == NULL || fd < 0 || events->nb_fd == 0) {
 178                 goto error;
 179         }
 180
 181         ret = epoll_ctl(events->epfd, EPOLL_CTL_DEL, fd, NULL);
 182         if (ret < 0) {
 183                 switch (errno) {
 184                 case ENOENT:
 185                 case EPERM:
 186                         /* Print PERROR and goto end not failing. Show must go on. */
 187                         PERROR("epoll_ctl DEL");
 188                         goto end;
 189                 default:
 190                         PERROR("epoll_ctl DEL fatal");
 191                         goto error;
 192                 }
 193         }
 194
 195         events->nb_fd--;
 196
 197 end:
 198         return 0;
 199
 200 error:
 201         return -1;
 202 }
 203
 204 /*
 205  * Set an fd's events.
 206  */
 207 LTTNG_HIDDEN
 208 int compat_epoll_mod(struct lttng_poll_event *events, int fd, uint32_t req_events)
 209 {
 210         int ret;
 211         struct epoll_event ev;
 212
 213         if (events == NULL || fd < 0 || events->nb_fd == 0) {
 214                 goto error;
 215         }
 216
 217         /*
 218          * Zero struct epoll_event to ensure all representations of its
 219          * union are zeroed.
 220          */
 221         memset(&ev, 0, sizeof(ev));
 222         ev.events = req_events;
 223         ev.data.fd = fd;
 224
 225         ret = epoll_ctl(events->epfd, EPOLL_CTL_MOD, fd, &ev);
 226         if (ret < 0) {
 227                 switch (errno) {
 228                 case ENOENT:
 229                 case EPERM:
 230                         /* Print PERROR and goto end not failing. Show must go on. */
 231                         PERROR("epoll_ctl MOD");
 232                         goto end;
 233                 default:
 234                         PERROR("epoll_ctl MOD fatal");
 235                         goto error;
 236                 }
 237         }
 238
 239 end:
 240         return 0;
 241
 242 error:
 243         return -1;
 244 }
 245
 246 /*
 247  * Wait on epoll set. This is a blocking call of timeout value.
 248  */
 249 LTTNG_HIDDEN
 250 int compat_epoll_wait(struct lttng_poll_event *events, int timeout,
 251                 bool interruptible)
 252 {
 253         int ret;
 254         uint32_t new_size;
 255
 256         if (events == NULL || events->events == NULL) {
 257                 ERR("Wrong arguments in compat_epoll_wait");
 258                 goto error;
 259         }
 260
 261         if (events->nb_fd == 0) {
 262                 errno = EINVAL;
 263                 return -1;
 264         }
 265
 266         /*
 267          * Resize if needed before waiting. We could either expand the array or
 268          * shrink it down. It's important to note that after this step, we are
 269          * ensured that the events argument of the epoll_wait call will be large
 270          * enough to hold every possible returned events.
 271          */
 272         new_size = 1U << utils_get_count_order_u32(events->nb_fd);
 273         if (new_size != events->alloc_size && new_size >= events->init_size) {
 274                 ret = resize_poll_event(events, new_size);
 275                 if (ret < 0) {
 276                         /* ENOMEM problem at this point. */
 277                         goto error;
 278                 }
 279         }
 280
 281         do {
 282                 ret = epoll_wait(events->epfd, events->events, events->nb_fd, timeout);
 283         } while (!interruptible && ret == -1 && errno == EINTR);
 284         if (ret < 0) {
 285                 if (errno != EINTR) {
 286                         PERROR("epoll_wait");
 287                 }
 288                 goto error;
 289         }
 290
 291         /*
 292          * Since the returned events are set sequentially in the "events" structure
 293          * we only need to return the epoll_wait value and iterate over it.
 294          */
 295         return ret;
 296
 297 error:
 298         return -1;
 299 }
 300
 301 /*
 302  * Setup poll set maximum size.
 303  */
 304 LTTNG_HIDDEN
 305 int compat_epoll_set_max_size(void)
 306 {
 307         int ret, fd, retval = 0;
 308         ssize_t size_ret;
 309         char buf[64];
 310
 311         fd = open(COMPAT_EPOLL_PROC_PATH, O_RDONLY);
 312         if (fd < 0) {
 313                 /*
 314                  * Failing on opening [1] is not an error per see. [1] was
 315                  * introduced in Linux 2.6.28 but epoll is available since
 316                  * 2.5.44. Hence, goto end and set a default value without
 317                  * setting an error return value.
 318                  *
 319                  * [1] /proc/sys/fs/epoll/max_user_watches
 320                  */
 321                 retval = 0;
 322                 goto end;
 323         }
 324
 325         size_ret = lttng_read(fd, buf, sizeof(buf));
 326         /*
 327          * Allow reading a file smaller than buf, but keep space for
 328          * final \0.
 329          */
 330         if (size_ret < 0 || size_ret >= sizeof(buf)) {
 331                 PERROR("read set max size");
 332                 retval = -1;
 333                 goto end_read;
 334         }
 335         buf[size_ret] = '\0';
 336         poll_max_size = atoi(buf);
 337 end_read:
 338         ret = close(fd);
 339         if (ret) {
 340                 PERROR("close");
 341         }
 342 end:
 343         if (!poll_max_size) {
 344                 poll_max_size = DEFAULT_POLL_SIZE;
 345         }
 346         DBG("epoll set max size is %d", poll_max_size);
 347         return retval;
 348 }