limit the inode and dentry cache via parameter in fuse_init

fs/fuse/control.c

@@ -184,6 +184,28 @@ static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
 	return ret;
 }
 
+static ssize_t fuse_conn_inode_count_read(struct file *file, char __user *buf,
+					   size_t len, loff_t *ppos)
+{
+	struct fuse_conn *fc;
+	unsigned long count;
+	char tmp[32];
+	size_t size;
+
+	if (*ppos)
+		return 0;
+
+	fc = fuse_ctl_file_conn_get(file);
+	if (!fc)
+		return 0;
+
+	count = atomic64_read(&fc->num_inodes);
+	fuse_conn_put(fc);
+
+	size = sprintf(tmp, "%lu\n", count);
+	return simple_read_from_buffer(buf, len, ppos, tmp, size);
+}
+
 static const struct file_operations fuse_ctl_abort_ops = {
 	.open = nonseekable_open,
 	.write = fuse_conn_abort_write,
@@ -210,6 +232,12 @@ static const struct file_operations fuse_conn_congestion_threshold_ops = {
 	.llseek = no_llseek,
 };
 
+static const struct file_operations fuse_conn_inode_count_ops = {
+	.open = nonseekable_open,
+	.read = fuse_conn_inode_count_read,
+	.llseek = no_llseek,
+};
+
 static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
 					  struct fuse_conn *fc,
 					  const char *name,
@@ -278,7 +306,9 @@ int fuse_ctl_add_conn(struct fuse_conn *fc)
 				 1, NULL, &fuse_conn_max_background_ops) ||
 	    !fuse_ctl_add_dentry(parent, fc, "congestion_threshold",
 				 S_IFREG | 0600, 1, NULL,
-				 &fuse_conn_congestion_threshold_ops))
+				 &fuse_conn_congestion_threshold_ops) ||
+	    !fuse_ctl_add_dentry(parent, fc, "inode_count", S_IFREG | 0400, 1,
+				 NULL, &fuse_conn_inode_count_ops))
 		goto err;
 
 	return 0;

fs/fuse/fuse_i.h

@@ -47,7 +47,7 @@
 #define FUSE_NAME_MAX (PATH_MAX - 1)
 
 /** Number of dentries for each connection in the control filesystem */
-#define FUSE_CTL_NUM_DENTRIES 5
+#define FUSE_CTL_NUM_DENTRIES 6
 
 /** Maximum of max_pages received in init_out */
 extern unsigned int fuse_max_pages_limit;
@@ -899,6 +899,8 @@ struct fuse_conn {
 	/** Version counter for evict inode */
 	atomic64_t evict_ctr;
 
+	atomic64_t num_inodes;
+
 	/* maximum file name length */
 	u32 name_max;
 

fs/fuse/inode.c

@@ -182,6 +182,7 @@ static void fuse_evict_inode(struct inode *inode)
 		 */
 		if (inode->i_nlink > 0)
 			atomic64_inc(&fc->evict_ctr);
+		atomic64_dec(&fc->num_inodes);
 	}
 	if (S_ISREG(inode->i_mode) && !fuse_is_bad(inode)) {
 		WARN_ON(!list_empty(&fi->write_files));
@@ -504,6 +505,7 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
 		inode->i_generation = generation;
 		fuse_init_inode(inode, attr, fc);
 		unlock_new_inode(inode);
+		atomic64_inc(&fc->num_inodes);
 	} else if (fuse_stale_inode(inode, generation, attr)) {
 		/* nodeid was reused, any I/O on the old inode should fail */
 		fuse_make_bad(inode);
@@ -1036,6 +1038,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 
 	atomic64_set(&fc->attr_version, 1);
 	atomic64_set(&fc->evict_ctr, 1);
+	atomic64_set(&fc->num_inodes, 0);
 	get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
 	fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
 	fc->user_ns = get_user_ns(user_ns);

include/uapi/linux/fuse.h

@@ -905,9 +905,6 @@ struct fuse_init_in {
 #define FUSE_COMPAT_INIT_OUT_SIZE 8
 #define FUSE_COMPAT_22_INIT_OUT_SIZE 24
 
-/*
- * align_page_order: Number of pages for optimal IO, or a multiple of that
- */
 struct fuse_init_out {
 	uint32_t	major;
 	uint32_t	minor;