Fix: poll and epoll fd set reallocation

[lttng-tools.git] / src / common / compat / compat-epoll.c

diff --git a/src/common/compat/compat-epoll.c b/src/common/compat/compat-epoll.c
index e1672c4c3178afbbce32acddebf2b30cea66fe09..40451b3d21286106430c1322209b21d9fef9579f 100644 (file)
--- a/src/common/compat/compat-epoll.c
+++ b/src/common/compat/compat-epoll.c
@@ -16,6 +16,7 @@
  */
 
 #define _GNU_SOURCE
+#include <assert.h>
 #include <fcntl.h>
 #include <limits.h>
 #include <stdlib.h>
@@ -31,6 +32,32 @@
 
 unsigned int poll_max_size;
 
+/*
+ * Resize the epoll events structure of the new size.
+ *
+ * Return 0 on success or else -1 with the current events pointer untouched.
+ */
+static int resize_poll_event(struct lttng_poll_event *events,
+               uint32_t new_size)
+{
+       struct epoll_event *ptr;
+
+       assert(events);
+
+       ptr = realloc(events->events, new_size * sizeof(*ptr));
+       if (ptr == NULL) {
+               PERROR("realloc epoll add");
+               goto error;
+       }
+       events->events = ptr;
+       events->alloc_size = new_size;
+
+       return 0;
+
+error:
+       return -1;
+}
+
 /*
  * Create epoll set and allocate returned events structure.
  */
@@ -63,7 +90,7 @@ int compat_epoll_create(struct lttng_poll_event *events, int size, int flags)
                goto error_close;
        }
 
-       events->events_size = size;
+       events->alloc_size = events->init_size = size;
        events->nb_fd = 0;
 
        return 0;
@@ -82,8 +109,8 @@ error:
  */
 int compat_epoll_add(struct lttng_poll_event *events, int fd, uint32_t req_events)
 {
-       int ret, new_size;
-       struct epoll_event ev, *ptr;
+       int ret;
+       struct epoll_event ev;
 
        if (events == NULL || events->events == NULL || fd < 0) {
                ERR("Bad compat epoll add arguments");
@@ -112,17 +139,6 @@ int compat_epoll_add(struct lttng_poll_event *events, int fd, uint32_t req_event
 
        events->nb_fd++;
 
-       if (events->nb_fd >= events->events_size) {
-               new_size = 2 * events->events_size;
-               ptr = realloc(events->events, new_size * sizeof(struct epoll_event));
-               if (ptr == NULL) {
-                       PERROR("realloc epoll add");
-                       goto error;
-               }
-               events->events = ptr;
-               events->events_size = new_size;
-       }
-
 end:
        return 0;
 
@@ -172,13 +188,39 @@ error:
 int compat_epoll_wait(struct lttng_poll_event *events, int timeout)
 {
        int ret;
+       uint32_t new_size;
 
-       if (events == NULL || events->events == NULL ||
-                       events->events_size < events->nb_fd) {
+       if (events == NULL || events->events == NULL) {
                ERR("Wrong arguments in compat_epoll_wait");
                goto error;
        }
 
+       /*
+        * Resize if needed before waiting. We could either expand the array or
+        * shrink it down. It's important to note that after this step, we are
+        * ensured that the events argument of the epoll_wait call will be large
+        * enough to hold every possible returned events.
+        */
+       if (events->nb_fd > events->alloc_size) {
+               /* Expand if the nb_fd is higher than the actual size. */
+               new_size = events->alloc_size << 1UL;
+       } else if ((events->nb_fd << 1UL) <= events->alloc_size &&
+                       events->nb_fd >= events->init_size) {
+               /* Shrink if nb_fd multiplied by two is <= than the actual size. */
+               new_size = events->alloc_size >> 1UL;
+       } else {
+               /* Indicate that we don't want to resize. */
+               new_size = 0;
+       }
+
+       if (new_size) {
+               ret = resize_poll_event(events, new_size);
+               if (ret < 0) {
+                       /* ENOMEM problem at this point. */
+                       goto error;
+               }
+       }
+
        do {
                ret = epoll_wait(events->epfd, events->events, events->nb_fd, timeout);
        } while (ret == -1 && errno == EINTR);
@@ -220,7 +262,7 @@ void compat_epoll_set_max_size(void)
        }
 
        poll_max_size = atoi(buf);
-       if (poll_max_size <= 0) {
+       if (poll_max_size == 0) {
                /* Extra precaution */
                poll_max_size = DEFAULT_POLL_SIZE;
        }