Add interfaces to get FDs from clients over the socket

This adds two interfaces:

    void SetReqFds(ClientPtr client, int req_fds)

	Marks the number of file descriptors expected for this
	request. Call this before any request processing so that
	any un-retrieved file descriptors will be closed
	automatically.

    int ReadFdFromClient(ClientPtr client)

	Reads the next queued file descriptor from the connection. If
	this request is not expecting any more file descriptors, or
	if there are no more file descriptors available from the
	connection, then this will return -1.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

include/dixstruct.h

@@ -110,8 +110,16 @@ typedef struct _Client {
 
     DeviceIntPtr clientPtr;
     ClientIdPtr clientIds;
+    int req_fds;
 } ClientRec;
 
+static inline void
+SetReqFds(ClientPtr client, int req_fds) {
+    if (client->req_fds != 0 && req_fds != client->req_fds)
+        LogMessage(X_ERROR, "Mismatching number of request fds %d != %d\n", req_fds, client->req_fds);
+    client->req_fds = req_fds;
+}
+
 /*
  * Scheduling interface
  */

include/os.h

@@ -98,6 +98,8 @@ extern _X_EXPORT int WaitForSomething(int *     /*pClientsReady */
 
 extern _X_EXPORT int ReadRequestFromClient(ClientPtr /*client */ );
 
+extern _X_EXPORT int ReadFdFromClient(ClientPtr client);
+
 extern _X_EXPORT Bool InsertFakeRequest(ClientPtr /*client */ ,
                                         char * /*data */ ,
                                         int /*count */ );

os/io.c

@@ -259,6 +259,12 @@ ReadRequestFromClient(ClientPtr client)
         oc->input = oci;
     }
 
+    /* Discard any unused file descriptors */
+    while (client->req_fds > 0) {
+        int req_fd = ReadFdFromClient(client);
+        if (req_fd >= 0)
+            close(req_fd);
+    }
     /* advance to start of next request */
 
     oci->bufptr += oci->lenLastReq;
@@ -485,6 +491,21 @@ ReadRequestFromClient(ClientPtr client)
     return needed;
 }
 
+int
+ReadFdFromClient(ClientPtr client)
+{
+    int fd = -1;
+
+    if (client->req_fds > 0) {
+        OsCommPtr oc = (OsCommPtr) client->osPrivate;
+
+        --client->req_fds;
+        fd = _XSERVTransRecvFd(oc->trans_conn);
+    } else
+        LogMessage(X_ERROR, "Request asks for FD without setting req_fds\n");
+    return fd;
+}
+
 /*****************************************************************
  * InsertFakeRequest
  *    Splice a consed up (possibly partial) request in as the next request.