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, 8 insertions, 0 deletions

diff --git a/example/notify_store_retrieve.c b/example/notify_store_retrieve.c
index 1298591..7145bf4 100644
--- a/example/notify_store_retrieve.c
+++ b/example/notify_store_retrieve.c
@@ -132,6 +132,13 @@ static int tfs_stat(fuse_ino_t ino, struct stat *stbuf) {
     return 0;
 }
 
+static void tfs_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 tfs_lookup(fuse_req_t req, fuse_ino_t parent,
                        const char *name) {
     struct fuse_entry_param e;
@@ -304,6 +311,7 @@ static void tfs_destroy(void *userdata)
 
 
 static const struct fuse_lowlevel_ops tfs_oper = {
+    .init       = tfs_init,
     .lookup	= tfs_lookup,
     .getattr	= tfs_getattr,
     .readdir	= tfs_readdir,