Fix bug #8197 - winbind does not properly detect when a DC connection is dead.

Only waiting for writability doesn't get fd errors back with poll.
So always begin by selecting for readability, and if we get it then
see if bytes were available to read or it really is an error condition.

If bytes were available, remove the select on read as we know we
will retrieve the error when we've finished writing and start
reading the reply (or the write will timeout or fail).

Metze and Volker please check.

Autobuild-User: Jeremy Allison <jra@samba.org>
Autobuild-Date: Mon Jun  6 21:53:16 CEST 2011 on sn-devel-104

1 files changed, 32 insertions, 6 deletions

diff --git a/lib/async_req/async_sock.c b/lib/async_req/async_sock.c
index 86053d94e87..dfb1a1cdbd7 100644
--- a/lib/async_req/async_sock.c
+++ b/lib/async_req/async_sock.c
@@ -386,6 +386,7 @@ struct writev_state {
 	int count;
 	size_t total_size;
 	uint16_t flags;
+	bool err_on_readability;
 };
 
 static void writev_trigger(struct tevent_req *req, void *private_data);
@@ -413,10 +414,8 @@ struct tevent_req *writev_send(TALLOC_CTX *mem_ctx, struct tevent_context *ev,
 	if (state->iov == NULL) {
 		goto fail;
 	}
-	state->flags = TEVENT_FD_WRITE;
-	if (err_on_readability) {
-		state->flags |= TEVENT_FD_READ;
-	}
+	state->flags = TEVENT_FD_WRITE|TEVENT_FD_READ;
+	state->err_on_readability = err_on_readability;
 
 	if (queue == NULL) {
 		struct tevent_fd *fde;
@@ -462,8 +461,35 @@ static void writev_handler(struct tevent_context *ev, struct tevent_fd *fde,
 	to_write = 0;
 
 	if ((state->flags & TEVENT_FD_READ) && (flags & TEVENT_FD_READ)) {
-		tevent_req_error(req, EPIPE);
-		return;
+		int ret, value;
+
+		if (state->err_on_readability) {
+			/* Readable and the caller wants an error on read. */
+			tevent_req_error(req, EPIPE);
+			return;
+		}
+
+		/* Might be an error. Check if there are bytes to read */
+		ret = ioctl(state->fd, FIONREAD, &value);
+		/* FIXME - should we also check
+		   for ret == 0 and value == 0 here ? */
+		if (ret == -1) {
+			/* There's an error. */
+			tevent_req_error(req, EPIPE);
+			return;
+		}
+		/* A request for TEVENT_FD_READ will succeed from now and
+		   forevermore until the bytes are read so if there was
+		   an error we'll wait until we do read, then get it in
+		   the read callback function. Until then, remove TEVENT_FD_READ
+		   from the flags we're waiting for. */
+		state->flags &= ~TEVENT_FD_READ;
+		TEVENT_FD_NOT_READABLE(fde);
+
+		/* If not writable, we're done. */
+		if (!(flags & TEVENT_FD_WRITE)) {
+			return;
+		}
 	}
 
 	for (i=0; i<state->count; i++) {