core: Be more efficient by not passing internal fds to backend

There are a number of fds that the core uses internally. Currently
any events on these fds are masked out so that the backend will
skip over them during handle_events().

This change improves upon this by simply not providing these fds
to the backend.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>

diff --git a/libusb/io.c b/libusb/io.c
index 8377a5e..430f67e 100644 (file)
--- a/libusb/io.c
+++ b/libusb/io.c
@@ -1961,11 +1961,27 @@ static int handle_events(struct libusb_context *ctx, struct timeval *tv)
        int r;
        struct usbi_pollfd *ipollfd;
        POLL_NFDS_TYPE nfds = 0;
+       POLL_NFDS_TYPE internal_nfds;
        struct pollfd *fds = NULL;
        int i = -1;
        int timeout_ms;
        int special_event;
 
+       /* there are certain fds that libusb uses internally, currently:
+        *
+        *   1) control pipe
+        *   2) hotplug pipe
+        *   3) timerfd
+        *
+        * the backend will never need to attempt to handle events on these fds, so
+        * we determine how many fds are in use internally for this context and when
+        * handle_events() is called in the backend, the pollfd list and count will
+        * be adjusted to skip over these internal fds */
+       if (usbi_using_timerfd(ctx))
+               internal_nfds = 3;
+       else
+               internal_nfds = 2;
+
        usbi_mutex_lock(&ctx->pollfds_lock);
        list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
                nfds++;
@@ -2019,14 +2035,8 @@ redo_poll:
                 * simply return */
                usbi_dbg("caught a fish on the control pipe");
 
-               if (r == 1) {
-                       r = 0;
+               if (0 == --r)
                        goto handled;
-               } else {
-                       /* prevent OS backend from trying to handle events on ctrl pipe */
-                       fds[0].revents = 0;
-                       r--;
-               }
        }
 
        /* fd[1] is always the hotplug pipe */
@@ -2052,8 +2062,7 @@ redo_poll:
                if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == message.event)
                        libusb_unref_device(message.device);
 
-               fds[1].revents = 0;
-               if (1 == r--)
+               if (0 == --r)
                        goto handled;
        } /* else there shouldn't be anything on this pipe */
 
@@ -2070,28 +2079,22 @@ redo_poll:
                        /* return error code */
                        r = ret;
                        goto handled;
-               } else if (r == 1) {
-                       /* no more active file descriptors, nothing more to do */
-                       r = 0;
-                       goto handled;
-               } else {
-                       /* more events pending...
-                        * prevent OS backend from trying to handle events on timerfd */
-                       fds[2].revents = 0;
-                       r--;
                }
+
+               if (0 == --r)
+                       goto handled;
        }
 #endif
 
-       r = usbi_backend->handle_events(ctx, fds, nfds, r);
+       r = usbi_backend->handle_events(ctx, fds + internal_nfds, nfds - internal_nfds, r);
        if (r)
                usbi_err(ctx, "backend handle_events failed with error %d", r);
 
 handled:
-        if (r == 0 && special_event) {
-                timeout_ms = 0;
-                goto redo_poll;
-        }
+       if (r == 0 && special_event) {
+               timeout_ms = 0;
+               goto redo_poll;
+       }
 
        free(fds);
        return r;