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, 9 insertions, 0 deletions

diff --git a/example/cuse.c b/example/cuse.c
index 0c0e7bc..6b33302 100644
--- a/example/cuse.c
+++ b/example/cuse.c
@@ -87,6 +87,14 @@ static int cusexmp_expand(size_t new_size)
 	return 0;
 }
 
+static void cusexmp_init(void *userdata, struct fuse_conn_info *conn)
+{
+	(void)userdata;
+
+	/* Disable the receiving and processing of FUSE_INTERRUPT requests */
+	conn->no_interrupt = 1;
+}
+
 static void cusexmp_open(fuse_req_t req, struct fuse_file_info *fi)
 {
 	fuse_reply_open(req, fi);
@@ -281,6 +289,7 @@ static int cusexmp_process_arg(void *data, const char *arg, int key,
 }
 
 static const struct cuse_lowlevel_ops cusexmp_clop = {
+	.init           = cusexmp_init,
 	.open		= cusexmp_open,
 	.read		= cusexmp_read,
 	.write		= cusexmp_write,