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.

11 files changed, 93 insertions, 10 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,
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,
diff --git a/example/hello_ll_uds.c b/example/hello_ll_uds.c
index f291fed..a566155 100644
--- a/example/hello_ll_uds.c
+++ b/example/hello_ll_uds.c
@@ -77,6 +77,14 @@ static void hello_ll_getattr(fuse_req_t req, fuse_ino_t ino,
 		fuse_reply_attr(req, &stbuf, 1.0);
 }
 
+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_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
 {
 	struct fuse_entry_param e;
@@ -164,6 +172,7 @@ static void hello_ll_read(fuse_req_t req, fuse_ino_t ino, size_t size,
 }
 
 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,
diff --git a/example/notify_inval_entry.c b/example/notify_inval_entry.c
index 83b24d2..c307899 100644
--- a/example/notify_inval_entry.c
+++ b/example/notify_inval_entry.c
@@ -140,6 +140,13 @@ 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;
@@ -232,6 +239,7 @@ static void tfs_readdir(fuse_req_t req, fuse_ino_t ino, size_t size,
 }
 
 static const struct fuse_lowlevel_ops tfs_oper = {
+    .init       = tfs_init,
     .lookup	= tfs_lookup,
     .getattr	= tfs_getattr,
     .readdir	= tfs_readdir,
diff --git a/example/notify_inval_inode.c b/example/notify_inval_inode.c
index c0b1112..de88c87 100644
--- a/example/notify_inval_inode.c
+++ b/example/notify_inval_inode.c
@@ -123,6 +123,13 @@ 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_destroy(void *userarg)
 {
     (void)userarg;
@@ -250,6 +257,7 @@ static void tfs_read(fuse_req_t req, fuse_ino_t ino, size_t size,
 }
 
 static const struct fuse_lowlevel_ops tfs_oper = {
+    .init       = tfs_init,
     .destroy    = tfs_destroy,
     .lookup	= tfs_lookup,
     .getattr	= tfs_getattr,
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,
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;
 }
 
 
diff --git a/example/passthrough_ll.c b/example/passthrough_ll.c
index da9de53..87c18a2 100644
--- a/example/passthrough_ll.c
+++ b/example/passthrough_ll.c
@@ -181,6 +181,9 @@ static void lo_init(void *userdata,
 			fuse_log(FUSE_LOG_DEBUG, "lo_init: activating flock locks\n");
 		conn->want |= FUSE_CAP_FLOCK_LOCKS;
 	}
+
+	/* Disable the receiving and processing of FUSE_INTERRUPT requests */
+	conn->no_interrupt = 1;
 }
 
 static void lo_destroy(void *userdata)
diff --git a/include/fuse_common.h b/include/fuse_common.h
index ba4b127..c583af3 100644
--- a/include/fuse_common.h
+++ b/include/fuse_common.h
@@ -635,9 +635,19 @@ struct fuse_conn_info {
 	unsigned max_backing_stack_depth;
 
 	/**
+	 * Disable FUSE_INTERRUPT requests.
+	 *
+	 * Enable `no_interrupt` option to:
+	 * 1) Avoid unnecessary locking operations and list operations,
+	 * 2) Return ENOSYS for the reply of FUSE_INTERRUPT request to
+	 * inform the kernel not to send the FUSE_INTERRUPT request.
+	 */
+	unsigned no_interrupt;
+
+	/**
 	 * For future use.
 	 */
-	unsigned reserved[21];
+	unsigned reserved[20];
 };
 
 struct fuse_session;
diff --git a/lib/fuse.c b/lib/fuse.c
index 8617168..4f06da7 100644
--- a/lib/fuse.c
+++ b/lib/fuse.c
@@ -2612,6 +2612,10 @@ static void fuse_lib_init(void *data, struct fuse_conn_info *conn)
 	if(conn->capable & FUSE_CAP_EXPORT_SUPPORT)
 		conn->want |= FUSE_CAP_EXPORT_SUPPORT;
 	fuse_fs_init(f->fs, conn, &f->conf);
+
+	/* Disable the receiving and processing of FUSE_INTERRUPT requests */
+	if (!f->conf.intr)
+		conn->no_interrupt = 1;
 }
 
 void fuse_fs_destroy(struct fuse_fs *fs)
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);