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/hello_ll.c b/example/hello_ll.c
index 10f4b4a..28bd1c4 100644
--- a/example/hello_ll.c
+++ b/example/hello_ll.c
@@ -53,6 +53,14 @@ static int hello_stat(fuse_ino_t ino, struct stat *stbuf)
 	return 0;
 }
 
+static void hello_ll_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 hello_ll_getattr(fuse_req_t req, fuse_ino_t ino,
 			     struct fuse_file_info *fi)
 {
@@ -202,6 +210,7 @@ static void hello_ll_removexattr(fuse_req_t req, fuse_ino_t ino, const char *nam
 }
 
 static const struct fuse_lowlevel_ops hello_ll_oper = {
+	.init = hello_ll_init,
 	.lookup = hello_ll_lookup,
 	.getattr = hello_ll_getattr,
 	.readdir = hello_ll_readdir,