[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

[akpm@osdl.org: fix this fs for recent dhowells depredations]
[akpm@osdl.org: fix 64-bit printk warnings]
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 218 insertions, 0 deletions

diff --git a/fs/fuse/control.c b/fs/fuse/control.c
new file mode 100644
index 000000000000..a3bce3a77253
--- /dev/null
+++ b/fs/fuse/control.c
@@ -0,0 +1,218 @@
+/*
+  FUSE: Filesystem in Userspace
+  Copyright (C) 2001-2006  Miklos Szeredi <miklos@szeredi.hu>
+
+  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);
+}