Add support for no_interrupt (#956)

The function fuse_session_process_buf_int() would do much things
for FUSE_INTERRUPT requests, even there are no FUSE_INTERRUPT requests:

1. check every non-FUSE_INTERRUPT request and add these requests to the
linked list(se->list) under a big lock(se->lock).
2. the function fuse_free_req() frees every request and remove them from
the linked list(se->list) under a bing lock(se->lock).

These operations are not meaningful when there are no FUSE_INTERRUPT requests,
and have a great impact on the performance of fuse filesystem because the big
lock for each request.

In some cases, FUSE_INTERRUPT requests are infrequent, even none at all.
Besides, the user-defined filesystem may do nothing for FUSE_INTERRUPT requests.

And the kernel side has the option "no_interrupt" in struct fuse_conn. This kernel option
can be enabled by return ENOSYS in libfuse for the reply of FUSE_INTERRUPT request.
But I don't find the code to enable the "no_interrupt" kernel option in libfuse.

So add the no_interrupt support, and when this operaion is enabled:
1. remove the useless locking operaions and list operations.
2. return ENOSYS for the reply of FUSE_INTERRUPT request to inform the kernel to disable
FUSE_INTERRUPT request.

1 files changed, 21 insertions, 9 deletions

diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
index dc1b7a6..92f7a99 100644
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -134,14 +134,20 @@ void fuse_free_req(fuse_req_t req)
 	int ctr;
 	struct fuse_session *se = req->se;
 
-	pthread_mutex_lock(&se->lock);
-	req->u.ni.func = NULL;
-	req->u.ni.data = NULL;
-	list_del_req(req);
-	ctr = --req->ctr;
-	fuse_chan_put(req->ch);
-	req->ch = NULL;
-	pthread_mutex_unlock(&se->lock);
+	if (se->conn.no_interrupt) {
+		ctr = --req->ctr;
+		fuse_chan_put(req->ch);
+		req->ch = NULL;
+	} else {
+		pthread_mutex_lock(&se->lock);
+		req->u.ni.func = NULL;
+		req->u.ni.data = NULL;
+		list_del_req(req);
+		ctr = --req->ctr;
+		fuse_chan_put(req->ch);
+		req->ch = NULL;
+		pthread_mutex_unlock(&se->lock);
+	}
 	if (!ctr)
 		destroy_req(req);
 }
@@ -2786,7 +2792,13 @@ void fuse_session_process_buf_int(struct fuse_session *se,
 	err = ENOSYS;
 	if (in->opcode >= FUSE_MAXOP || !fuse_ll_ops[in->opcode].func)
 		goto reply_err;
-	if (in->opcode != FUSE_INTERRUPT) {
+	/* Do not process interrupt request */
+	if (se->conn.no_interrupt && in->opcode == FUSE_INTERRUPT) {
+		if (se->debug)
+			fuse_log(FUSE_LOG_DEBUG, "FUSE_INTERRUPT: reply to kernel to disable interrupt\n");
+		goto reply_err;
+	}
+	if (!se->conn.no_interrupt && in->opcode != FUSE_INTERRUPT) {
 		struct fuse_req *intr;
 		pthread_mutex_lock(&se->lock);
 		intr = check_interrupt(se, req);