[PATCH] miext: Move SyncShm FDs out of the way of clients
Keith Packard
keithp at keithp.com
Fri Nov 22 11:41:06 PST 2013
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>
---
v2: Move to os/utils.c, make sure the new FD has the close-on-exec flag set.
include/os.h | 3 +++
miext/sync/misyncshm.c | 3 +++
os/utils.c | 23 +++++++++++++++++++++++
3 files changed, 29 insertions(+)
diff --git a/include/os.h b/include/os.h
index 450e1a8..9b67294 100644
--- a/include/os.h
+++ b/include/os.h
@@ -686,4 +686,7 @@ LogPrintMarkers(void);
extern _X_EXPORT void
xorg_backtrace(void);
+extern _X_EXPORT int
+os_move_fd(int fd);
+
#endif /* OS_H */
diff --git a/miext/sync/misyncshm.c b/miext/sync/misyncshm.c
index 3f9350a..20780fd 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;
@@ -126,6 +127,7 @@ miSyncShmCreateFenceFromFd(ScreenPtr pScreen, SyncFence *pFence, int fd, Bool in
miSyncInitFence(pScreen, pFence, initially_triggered);
+ fd = os_move_fd(fd);
pPriv->fence = xshmfence_map_shm(fd);
if (pPriv->fence) {
pPriv->fd = fd;
@@ -145,6 +147,7 @@ miSyncShmGetFenceFd(ScreenPtr pScreen, SyncFence *pFence)
pPriv->fd = xshmfence_alloc_shm();
if (pPriv->fd < 0)
return -1;
+ pPriv->fd = os_move_fd(pPriv->fd);
pPriv->fence = xshmfence_map_shm(pPriv->fd);
if (!pPriv->fence) {
close (pPriv->fd);
diff --git a/os/utils.c b/os/utils.c
index fb20da7..f3b53e8 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -2071,3 +2071,26 @@ FormatUInt64Hex(uint64_t num, char *string)
string[len] = '\0';
}
+
+/* Move a file descriptor out of the way of our select mask; this
+ * is useful for file descriptors which will never appear in the
+ * select mask to avoid reducing the number of clients that can
+ * connect to the server
+ */
+int
+os_move_fd(int fd)
+{
+ int newfd;
+
+#ifdef F_DUPFD_CLOEXEC
+ newfd = fcntl(fd, F_DUPFD_CLOEXEC, MAXCLIENTS);
+#else
+ newfd = fcntl(fd, F_DUPFD, MAXCLIENTS);
+#endif
+ if (newfd < 0)
+ return fd;
+#ifndef F_DUPFD_CLOEXEC
+ fcntl(newfd, F_SETFD, FD_CLOEXEC);
+#endif
+ return newfd;
+}
--
1.8.4.3
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