libxl: support multiple libxl__ev_fds for the same fd

We need a slightly more sophisticated data structure to allow this,
where we record the slot not just for each fd but also for each
(fd,eventbit) where eventbit is POLLIN, POLLPRI, POLLOUT.

Document the new relaxed restriction.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

Changes since v6:
 * Fix typo
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

1 files changed, 35 insertions, 27 deletions

diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index 5046938fd8..93c1d1f969 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -639,10 +639,11 @@ static int beforepoll_internal(libxl__gc *gc, libxl__poller *poller,
 
 
     /*
-     * In order to be able to efficiently find the libxl__ev_fd
-     * for a struct poll during _afterpoll, we maintain a shadow
-     * data structure in CTX->fd_beforepolled: each slot in
-     * the fds array corresponds to a slot in fd_beforepolled.
+     * In order to be able to efficiently find the libxl__ev_fd for a
+     * struct poll during _afterpoll, we maintain a shadow data
+     * structure in CTX->fd_rindices: each fd corresponds to a slot in
+     * fd_rindices, and each element in the rindices is three indices
+     * into the fd array (for POLLIN, POLLPRI and POLLOUT).
      */
 
     if (*nfds_io) {
@@ -663,14 +664,16 @@ static int beforepoll_internal(libxl__gc *gc, libxl__poller *poller,
         });
 
         /* make sure our array is as big as *nfds_io */
-        if (poller->fd_rindex_allocd < maxfd) {
-            assert(maxfd < INT_MAX / sizeof(int) / 2);
-            int *newarray = realloc(poller->fd_rindex, sizeof(int) * maxfd);
-            if (!newarray) { rc = ERROR_NOMEM; goto out; }
-            memset(newarray + poller->fd_rindex_allocd, 0,
-                   sizeof(int) * (maxfd - poller->fd_rindex_allocd));
-            poller->fd_rindex = newarray;
-            poller->fd_rindex_allocd = maxfd;
+        if (poller->fd_rindices_allocd < maxfd) {
+            assert(ARRAY_SIZE_OK(poller->fd_rindices, maxfd));
+            poller->fd_rindices =
+                libxl__realloc(0, poller->fd_rindices,
+                               maxfd * sizeof(*poller->fd_rindices));
+            memset(poller->fd_rindices + poller->fd_rindices_allocd,
+                   0,
+                   (maxfd - poller->fd_rindices_allocd)
+                     * sizeof(*poller->fd_rindices));
+            poller->fd_rindices_allocd = maxfd;
         }
     }
 
@@ -681,8 +684,10 @@ static int beforepoll_internal(libxl__gc *gc, libxl__poller *poller,
             fds[used].fd = req_fd;
             fds[used].events = req_events;
             fds[used].revents = 0;
-            assert(req_fd < poller->fd_rindex_allocd);
-            poller->fd_rindex[req_fd] = used;
+            assert(req_fd < poller->fd_rindices_allocd);
+            if (req_events & POLLIN)  poller->fd_rindices[req_fd][0] = used;
+            if (req_events & POLLPRI) poller->fd_rindices[req_fd][1] = used;
+            if (req_events & POLLOUT) poller->fd_rindices[req_fd][2] = used;
         }
         used++;
     });
@@ -710,7 +715,6 @@ static int beforepoll_internal(libxl__gc *gc, libxl__poller *poller,
             *timeout_upd = our_timeout;
     }
 
- out:
     return rc;
 }
 
@@ -732,24 +736,28 @@ static int afterpoll_check_fd(libxl__poller *poller,
                               int fd, int events)
     /* returns mask of events which were requested and occurred */
 {
-    if (fd >= poller->fd_rindex_allocd)
+    if (fd >= poller->fd_rindices_allocd)
         /* added after we went into poll, have to try again */
         return 0;
 
-    int slot = poller->fd_rindex[fd];
+    int i, revents = 0;
+    for (i=0; i<3; i++) {
+        int slot = poller->fd_rindices[fd][i];
 
-    if (slot >= nfds)
-        /* stale slot entry; again, added afterwards */
-        return 0;
+        if (slot >= nfds)
+            /* stale slot entry; again, added afterwards */
+            continue;
 
-    if (fds[slot].fd != fd)
-        /* again, stale slot entry */
-        return 0;
+        if (fds[slot].fd != fd)
+            /* again, stale slot entry */
+            continue;
 
-    assert(!(fds[slot].revents & POLLNVAL));
+        assert(!(fds[slot].revents & POLLNVAL));
+        revents |= fds[slot].revents;
+    }
 
-    int revents = fds[slot].revents & (events | POLLERR | POLLHUP);
     /* we mask in case requested events have changed */
+    revents &= (events | POLLERR | POLLHUP);
 
     return revents;
 }
@@ -1013,7 +1021,7 @@ int libxl__poller_init(libxl_ctx *ctx, libxl__poller *p)
 {
     int r, rc;
     p->fd_polls = 0;
-    p->fd_rindex = 0;
+    p->fd_rindices = 0;
 
     r = pipe(p->wakeup_pipe);
     if (r) {
@@ -1040,7 +1048,7 @@ void libxl__poller_dispose(libxl__poller *p)
     if (p->wakeup_pipe[1] > 0) close(p->wakeup_pipe[1]);
     if (p->wakeup_pipe[0] > 0) close(p->wakeup_pipe[0]);
     free(p->fd_polls);
-    free(p->fd_rindex);
+    free(p->fd_rindices);
 }
 
 libxl__poller *libxl__poller_get(libxl_ctx *ctx)