fuse: add fusectl interface to max_background

Make the max_background and congestion_threshold parameters of a FUSE
mount tunable at runtime by adding the respective knobs to its directory
within the fusectl filesystem.
Signed-off-by: Csaba Henk <csaba@gluster.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/control.c

@@ -61,6 +61,121 @@ static ssize_t fuse_conn_waiting_read(struct file *file, char __user *buf,
 	return simple_read_from_buffer(buf, len, ppos, tmp, size);
 }
 
+static ssize_t fuse_conn_limit_read(struct file *file, char __user *buf,
+				    size_t len, loff_t *ppos, unsigned val)
+{
+	char tmp[32];
+	size_t size = sprintf(tmp, "%u\n", val);
+
+	return simple_read_from_buffer(buf, len, ppos, tmp, size);
+}
+
+static ssize_t fuse_conn_limit_write(struct file *file, const char __user *buf,
+				     size_t count, loff_t *ppos, unsigned *val,
+				     unsigned global_limit)
+{
+	unsigned long t;
+	char tmp[32];
+	unsigned limit = (1 << 16) - 1;
+	int err;
+
+	if (*ppos || count >= sizeof(tmp) - 1)
+		return -EINVAL;
+
+	if (copy_from_user(tmp, buf, count))
+		return -EINVAL;
+
+	tmp[count] = '\0';
+
+	err = strict_strtoul(tmp, 0, &t);
+	if (err)
+		return err;
+
+	if (!capable(CAP_SYS_ADMIN))
+		limit = min(limit, global_limit);
+
+	if (t > limit)
+		return -EINVAL;
+
+	*val = t;
+
+	return count;
+}
+
+static ssize_t fuse_conn_max_background_read(struct file *file,
+					     char __user *buf, size_t len,
+					     loff_t *ppos)
+{
+	struct fuse_conn *fc;
+	unsigned val;
+
+	fc = fuse_ctl_file_conn_get(file);
+	if (!fc)
+		return 0;
+
+	val = fc->max_background;
+	fuse_conn_put(fc);
+
+	return fuse_conn_limit_read(file, buf, len, ppos, val);
+}
+
+static ssize_t fuse_conn_max_background_write(struct file *file,
+					      const char __user *buf,
+					      size_t count, loff_t *ppos)
+{
+	unsigned val;
+	ssize_t ret;
+
+	ret = fuse_conn_limit_write(file, buf, count, ppos, &val,
+				    max_user_bgreq);
+	if (ret > 0) {
+		struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
+		if (fc) {
+			fc->max_background = val;
+			fuse_conn_put(fc);
+		}
+	}
+
+	return ret;
+}
+
+static ssize_t fuse_conn_congestion_threshold_read(struct file *file,
+						   char __user *buf, size_t len,
+						   loff_t *ppos)
+{
+	struct fuse_conn *fc;
+	unsigned val;
+
+	fc = fuse_ctl_file_conn_get(file);
+	if (!fc)
+		return 0;
+
+	val = fc->congestion_threshold;
+	fuse_conn_put(fc);
+
+	return fuse_conn_limit_read(file, buf, len, ppos, val);
+}
+
+static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
+						    const char __user *buf,
+						    size_t count, loff_t *ppos)
+{
+	unsigned val;
+	ssize_t ret;
+
+	ret = fuse_conn_limit_write(file, buf, count, ppos, &val,
+				    max_user_congthresh);
+	if (ret > 0) {
+		struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
+		if (fc) {
+			fc->congestion_threshold = val;
+			fuse_conn_put(fc);
+		}
+	}
+
+	return ret;
+}
+
 static const struct file_operations fuse_ctl_abort_ops = {
 	.open = nonseekable_open,
 	.write = fuse_conn_abort_write,
@@ -71,6 +186,18 @@ static const struct file_operations fuse_ctl_waiting_ops = {
 	.read = fuse_conn_waiting_read,
 };
 
+static const struct file_operations fuse_conn_max_background_ops = {
+	.open = nonseekable_open,
+	.read = fuse_conn_max_background_read,
+	.write = fuse_conn_max_background_write,
+};
+
+static const struct file_operations fuse_conn_congestion_threshold_ops = {
+	.open = nonseekable_open,
+	.read = fuse_conn_congestion_threshold_read,
+	.write = fuse_conn_congestion_threshold_write,
+};
+
 static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
 					  struct fuse_conn *fc,
 					  const char *name,
@@ -129,7 +256,12 @@ int fuse_ctl_add_conn(struct fuse_conn *fc)
 	if (!fuse_ctl_add_dentry(parent, fc, "waiting", S_IFREG | 0400, 1,
 				 NULL, &fuse_ctl_waiting_ops) ||
 	    !fuse_ctl_add_dentry(parent, fc, "abort", S_IFREG | 0200, 1,
-				 NULL, &fuse_ctl_abort_ops))
+				 NULL, &fuse_ctl_abort_ops) ||
+	    !fuse_ctl_add_dentry(parent, fc, "max_background", S_IFREG | 0600,
+				 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))
 		goto err;
 
 	return 0;

fs/fuse/fuse_i.h

@@ -32,7 +32,7 @@
 #define FUSE_NAME_MAX 1024
 
 /** Number of dentries for each connection in the control filesystem */
-#define FUSE_CTL_NUM_DENTRIES 3
+#define FUSE_CTL_NUM_DENTRIES 5
 
 /** If the FUSE_DEFAULT_PERMISSIONS flag is given, the filesystem
     module will check permissions based on the file mode.  Otherwise no
@@ -49,6 +49,10 @@ extern struct list_head fuse_conn_list;
 /** Global mutex protecting fuse_conn_list and the control filesystem */
 extern struct mutex fuse_mutex;
 
+/** Module parameters */
+extern unsigned max_user_bgreq;
+extern unsigned max_user_congthresh;
+
 /** FUSE inode */
 struct fuse_inode {
 	/** Inode data */

fs/fuse/inode.c

@@ -31,7 +31,7 @@ DEFINE_MUTEX(fuse_mutex);
 
 static int set_global_limit(const char *val, struct kernel_param *kp);
 
-static unsigned max_user_bgreq;
+unsigned max_user_bgreq;
 module_param_call(max_user_bgreq, set_global_limit, param_get_uint,
 		  &max_user_bgreq, 0644);
 __MODULE_PARM_TYPE(max_user_bgreq, "uint");
@@ -39,7 +39,7 @@ MODULE_PARM_DESC(max_user_bgreq,
  "Global limit for the maximum number of backgrounded requests an "
  "unprivileged user can set");
 
-static unsigned max_user_congthresh;
+unsigned max_user_congthresh;
 module_param_call(max_user_congthresh, set_global_limit, param_get_uint,
 		  &max_user_congthresh, 0644);
 __MODULE_PARM_TYPE(max_user_congthresh, "uint");