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, 3 insertions, 0 deletions

diff --git a/example/passthrough_hp.cc b/example/passthrough_hp.cc
index 7b8febe..e780f23 100644
--- a/example/passthrough_hp.cc
+++ b/example/passthrough_hp.cc
@@ -223,6 +223,9 @@ static void sfs_init(void *userdata, fuse_conn_info *conn) {
     /* This is a local file system - no network coherency needed */
     if (conn->capable & FUSE_CAP_DIRECT_IO_ALLOW_MMAP)
         conn->want |= FUSE_CAP_DIRECT_IO_ALLOW_MMAP;
+
+    /* Disable the receiving and processing of FUSE_INTERRUPT requests */
+    conn->no_interrupt = 1;
 }