[PATCH] fuse: add control filesystem

Add a control filesystem to fuse, replacing the attributes currently exported
through sysfs.  An empty directory '/sys/fs/fuse/connections' is still created
in sysfs, and mounting the control filesystem here provides backward
compatibility.

Advantages of the control filesystem over the previous solution:

  - allows the object directory and the attributes to be owned by the
    filesystem owner, hence letting unpriviled users abort the
    filesystem connection

  - does not suffer from module unload race

[[email protected]: fix this fs for recent dhowells depredations]
[[email protected]: fix 64-bit printk warnings]
Signed-off-by: Miklos Szeredi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: szmi

Documentation/filesystems/fuse.txt

@@ -18,6 +18,14 @@ Non-privileged mount (or user mount):
   user.  NOTE: this is not the same as mounts allowed with the "user"
   option in /etc/fstab, which is not discussed here.
 
+Filesystem connection:
+
+  A connection between the filesystem daemon and the kernel.  The
+  connection exists until either the daemon dies, or the filesystem is
+  umounted.  Note that detaching (or lazy umounting) the filesystem
+  does _not_ break the connection, in this case it will exist until
+  the last reference to the filesystem is released.
+
 Mount owner:
 
   The user who does the mounting.
@@ -86,16 +94,20 @@ Mount options
   The default is infinite.  Note that the size of read requests is
   limited anyway to 32 pages (which is 128kbyte on i386).
 
-Sysfs
-~~~~~
+Control filesystem
+~~~~~~~~~~~~~~~~~~
+
+There's a control filesystem for FUSE, which can be mounted by:
 
-FUSE sets up the following hierarchy in sysfs:
+  mount -t fusectl none /sys/fs/fuse/connections
 
-  /sys/fs/fuse/connections/N/
+Mounting it under the '/sys/fs/fuse/connections' directory makes it
+backwards compatible with earlier versions.
 
-where N is an increasing number allocated to each new connection.
+Under the fuse control filesystem each connection has a directory
+named by a unique number.
 
-For each connection the following attributes are defined:
+For each connection the following files exist within this directory:
 
  'waiting'
 
@@ -110,7 +122,7 @@ For each connection the following attributes are defined:
   connection.  This means that all waiting requests will be aborted an
   error returned for all aborted and new requests.
 
-Only a privileged user may read or write these attributes.
+Only the owner of the mount may read or write these files.
 
 Aborting a filesystem connection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -139,8 +151,8 @@ the filesystem.  There are several ways to do this:
   - Use forced umount (umount -f).  Works in all cases but only if
     filesystem is still attached (it hasn't been lazy unmounted)
 
-  - Abort filesystem through the sysfs interface.  Most powerful
-    method, always works.
+  - Abort filesystem through the FUSE control filesystem.  Most
+    powerful method, always works.
 
 How do non-privileged mounts work?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

fs/fuse/Makefile

@@ -4,4 +4,4 @@
 
 obj-$(CONFIG_FUSE_FS) += fuse.o
 
-fuse-objs := dev.o dir.o file.o inode.o
+fuse-objs := dev.o dir.o file.o inode.o control.o

fs/fuse/control.c

@@ -0,0 +1,218 @@
+/*
+  FUSE: Filesystem in Userspace
+  Copyright (C) 2001-2006  Miklos Szeredi <[email protected]>
+
+  This program can be distributed under the terms of the GNU GPL.
+  See the file COPYING.
+*/
+
+#include "fuse_i.h"
+
+#include <linux/init.h>
+#include <linux/module.h>
+
+#define FUSE_CTL_SUPER_MAGIC 0x65735543
+
+/*
+ * This is non-NULL when the single instance of the control filesystem
+ * exists.  Protected by fuse_mutex
+ */
+static struct super_block *fuse_control_sb;
+
+static struct fuse_conn *fuse_ctl_file_conn_get(struct file *file)
+{
+	struct fuse_conn *fc;
+	mutex_lock(&fuse_mutex);
+	fc = file->f_dentry->d_inode->u.generic_ip;
+	if (fc)
+		fc = fuse_conn_get(fc);
+	mutex_unlock(&fuse_mutex);
+	return fc;
+}
+
+static ssize_t fuse_conn_abort_write(struct file *file, const char __user *buf,
+				     size_t count, loff_t *ppos)
+{
+	struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
+	if (fc) {
+		fuse_abort_conn(fc);
+		fuse_conn_put(fc);
+	}
+	return count;
+}
+
+static ssize_t fuse_conn_waiting_read(struct file *file, char __user *buf,
+				      size_t len, loff_t *ppos)
+{
+	char tmp[32];
+	size_t size;
+
+	if (!*ppos) {
+		struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
+		if (!fc)
+			return 0;
+
+		file->private_data=(void *)(long)atomic_read(&fc->num_waiting);
+		fuse_conn_put(fc);
+	}
+	size = sprintf(tmp, "%ld\n", (long)file->private_data);
+	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,
+};
+
+static const struct file_operations fuse_ctl_waiting_ops = {
+	.open = nonseekable_open,
+	.read = fuse_conn_waiting_read,
+};
+
+static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
+					  struct fuse_conn *fc,
+					  const char *name,
+					  int mode, int nlink,
+					  struct inode_operations *iop,
+					  const struct file_operations *fop)
+{
+	struct dentry *dentry;
+	struct inode *inode;
+
+	BUG_ON(fc->ctl_ndents >= FUSE_CTL_NUM_DENTRIES);
+	dentry = d_alloc_name(parent, name);
+	if (!dentry)
+		return NULL;
+
+	fc->ctl_dentry[fc->ctl_ndents++] = dentry;
+	inode = new_inode(fuse_control_sb);
+	if (!inode)
+		return NULL;
+
+	inode->i_mode = mode;
+	inode->i_uid = fc->user_id;
+	inode->i_gid = fc->group_id;
+	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+	/* setting ->i_op to NULL is not allowed */
+	if (iop)
+		inode->i_op = iop;
+	inode->i_fop = fop;
+	inode->i_nlink = nlink;
+	inode->u.generic_ip = fc;
+	d_add(dentry, inode);
+	return dentry;
+}
+
+/*
+ * Add a connection to the control filesystem (if it exists).  Caller
+ * must host fuse_mutex
+ */
+int fuse_ctl_add_conn(struct fuse_conn *fc)
+{
+	struct dentry *parent;
+	char name[32];
+
+	if (!fuse_control_sb)
+		return 0;
+
+	parent = fuse_control_sb->s_root;
+	parent->d_inode->i_nlink++;
+	sprintf(name, "%llu", (unsigned long long) fc->id);
+	parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500, 2,
+				     &simple_dir_inode_operations,
+				     &simple_dir_operations);
+	if (!parent)
+		goto err;
+
+	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))
+		goto err;
+
+	return 0;
+
+ err:
+	fuse_ctl_remove_conn(fc);
+	return -ENOMEM;
+}
+
+/*
+ * Remove a connection from the control filesystem (if it exists).
+ * Caller must host fuse_mutex
+ */
+void fuse_ctl_remove_conn(struct fuse_conn *fc)
+{
+	int i;
+
+	if (!fuse_control_sb)
+		return;
+
+	for (i = fc->ctl_ndents - 1; i >= 0; i--) {
+		struct dentry *dentry = fc->ctl_dentry[i];
+		dentry->d_inode->u.generic_ip = NULL;
+		d_drop(dentry);
+		dput(dentry);
+	}
+	fuse_control_sb->s_root->d_inode->i_nlink--;
+}
+
+static int fuse_ctl_fill_super(struct super_block *sb, void *data, int silent)
+{
+	struct tree_descr empty_descr = {""};
+	struct fuse_conn *fc;
+	int err;
+
+	err = simple_fill_super(sb, FUSE_CTL_SUPER_MAGIC, &empty_descr);
+	if (err)
+		return err;
+
+	mutex_lock(&fuse_mutex);
+	BUG_ON(fuse_control_sb);
+	fuse_control_sb = sb;
+	list_for_each_entry(fc, &fuse_conn_list, entry) {
+		err = fuse_ctl_add_conn(fc);
+		if (err) {
+			fuse_control_sb = NULL;
+			mutex_unlock(&fuse_mutex);
+			return err;
+		}
+	}
+	mutex_unlock(&fuse_mutex);
+
+	return 0;
+}
+
+static int fuse_ctl_get_sb(struct file_system_type *fs_type, int flags,
+			const char *dev_name, void *raw_data,
+			struct vfsmount *mnt)
+{
+	return get_sb_single(fs_type, flags, raw_data,
+				fuse_ctl_fill_super, mnt);
+}
+
+static void fuse_ctl_kill_sb(struct super_block *sb)
+{
+	mutex_lock(&fuse_mutex);
+	fuse_control_sb = NULL;
+	mutex_unlock(&fuse_mutex);
+
+	kill_litter_super(sb);
+}
+
+static struct file_system_type fuse_ctl_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "fusectl",
+	.get_sb		= fuse_ctl_get_sb,
+	.kill_sb	= fuse_ctl_kill_sb,
+};
+
+int __init fuse_ctl_init(void)
+{
+	return register_filesystem(&fuse_ctl_fs_type);
+}
+
+void fuse_ctl_cleanup(void)
+{
+	unregister_filesystem(&fuse_ctl_fs_type);
+}

fs/fuse/dev.c

@@ -833,7 +833,7 @@ static int fuse_dev_release(struct inode *inode, struct file *file)
 		end_requests(fc, &fc->processing);
 		spin_unlock(&fc->lock);
 		fasync_helper(-1, file, 0, &fc->fasync);
-		kobject_put(&fc->kobj);
+		fuse_conn_put(fc);
 	}
 
 	return 0;