[PATCH] miext: Move SyncShm FDs out of the way of clients

[Keith Packard]

Applications may end up allocating a bunch of shmfence objects, each
of which uses a file descriptor, which must be kept open lest some
other client ask for a copy of it later on.

Lacking an API that can turn a memory mapping back into a file
descriptor, about the best we can do is push the file descriptors out
of the way of other X clients so that we don't run out of the ability
to accept new connections.

This uses fcntl F_GETFD to push the FD up above MAXCLIENTS.

Signed-off-by: Keith Packard <keithp at keithp.com>
---

This patch has been added to my keithp-fixes branch

 miext/sync/misyncshm.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/miext/sync/misyncshm.c b/miext/sync/misyncshm.c
index 3f9350a..59f99fb 100644
--- a/miext/sync/misyncshm.c
+++ b/miext/sync/misyncshm.c
@@ -32,6 +32,7 @@
 #include "pixmapstr.h"
 #include <sys/mman.h>
 #include <unistd.h>
+#include <fcntl.h>
 #include <X11/xshmfence.h>
 
 static DevPrivateKeyRec syncShmFencePrivateKey;
@@ -120,12 +121,26 @@ miSyncShmScreenDestroyFence(ScreenPtr pScreen, SyncFence * pFence)
 }
 
 static int
+miSyncShmMoveFd(int fd)
+{
+    int newfd;
+
+    newfd = fcntl(fd, F_DUPFD, MAXCLIENTS);
+    if (newfd < 0)
+        return fd;
+
+    close(fd);
+    return newfd;
+}
+
+static int
 miSyncShmCreateFenceFromFd(ScreenPtr pScreen, SyncFence *pFence, int fd, Bool initially_triggered)
 {
     SyncShmFencePrivatePtr      pPriv = SYNC_FENCE_PRIV(pFence);
 
     miSyncInitFence(pScreen, pFence, initially_triggered);
 
+    fd = miSyncShmMoveFd(fd);
     pPriv->fence = xshmfence_map_shm(fd);
     if (pPriv->fence) {
         pPriv->fd = fd;
@@ -145,6 +160,7 @@ miSyncShmGetFenceFd(ScreenPtr pScreen, SyncFence *pFence)
         pPriv->fd = xshmfence_alloc_shm();
         if (pPriv->fd < 0)
             return -1;
+        pPriv->fd = miSyncShmMoveFd(pPriv->fd);
         pPriv->fence = xshmfence_map_shm(pPriv->fd);
         if (!pPriv->fence) {
             close (pPriv->fd);
-- 
1.8.4.2