[PATCH] fuse: add number of waiting requests attribute

This patch adds the 'waiting' attribute which indicates how many filesystem
requests are currently waiting to be completed. A non-zero value without any
filesystem activity indicates a hung or deadlocked filesystem.

Signed-off-by: Miklos Szeredi <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/fuse/dev.c

···
 	int intr;
 	sigset_t oldset;
 
+	atomic_inc(&fc->num_waiting);
 	block_sigs(&oldset);
 	intr = down_interruptible(&fc->outstanding_sem);
 	restore_sigs(&oldset);
-	return intr ? NULL : do_get_request(fc);
+	if (intr) {
+		atomic_dec(&fc->num_waiting);
+		return NULL;
+	}
+	return do_get_request(fc);
 }
 
 static void fuse_putback_request(struct fuse_conn *fc, struct fuse_req *req)
 {
 	spin_lock(&fuse_lock);
-	if (req->preallocated)
+	if (req->preallocated) {
+		atomic_dec(&fc->num_waiting);
 		list_add(&req->list, &fc->unused_list);
-	else
+	} else
 		fuse_request_free(req);
 
 	/* If we are in debt decrease that first */

fs/fuse/fuse_i.h

···
 	/** Is create not implemented by fs? */
 	unsigned no_create : 1;
 
+	/** The number of requests waiting for completion */
+	atomic_t num_waiting;
+
 	/** Negotiated minor version */
 	unsigned minor;
 

fs/fuse/inode.c

···
 	.kill_sb	= kill_anon_super,
 };
 
+static ssize_t fuse_conn_waiting_show(struct fuse_conn *fc, char *page)
+{
+	return sprintf(page, "%i\n", atomic_read(&fc->num_waiting));
+}
+
+static struct fuse_conn_attr fuse_conn_waiting =
+	__ATTR(waiting, 0400, fuse_conn_waiting_show, NULL);
+
 static struct attribute *fuse_conn_attrs[] = {
+	&fuse_conn_waiting.attr,
 	NULL,
 };