[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>

5 files changed, 310 insertions, 106 deletions

diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
index c3e1f760cac9..72437065f6ad 100644
--- a/fs/fuse/Makefile
+++ b/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
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);
+}
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index fec4779e2b55..fe3adf589174 100644
--- a/fs/fuse/dev.c
+++ b/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;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 25f8581a770c..ac12b01f4446 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -14,6 +14,7 @@
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/backing-dev.h>
+#include <linux/mutex.h>
 
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
@@ -24,6 +25,9 @@
 /** It could be as large as PATH_MAX, but would that have any uses? */
 #define FUSE_NAME_MAX 1024
 
+/** Number of dentries for each connection in the control filesystem */
+#define FUSE_CTL_NUM_DENTRIES 3
+
 /** If the FUSE_DEFAULT_PERMISSIONS flag is given, the filesystem
     module will check permissions based on the file mode.  Otherwise no
     permission checking is done in the kernel */
@@ -33,6 +37,11 @@
     doing the mount will be allowed to access the filesystem */
 #define FUSE_ALLOW_OTHER         (1 << 1)
 
+/** List of active connections */
+extern struct list_head fuse_conn_list;
+
+/** Global mutex protecting fuse_conn_list and the control filesystem */
+extern struct mutex fuse_mutex;
 
 /** FUSE inode */
 struct fuse_inode {
@@ -216,6 +225,9 @@ struct fuse_conn {
         /** Lock protecting accessess to  members of this structure */
         spinlock_t lock;
 
+        /** Refcount */
+        atomic_t count;
+
         /** The user id for this mount */
         uid_t user_id;
 
@@ -310,8 +322,17 @@ struct fuse_conn {
         /** Backing dev info */
         struct backing_dev_info bdi;
 
-        /** kobject */
-        struct kobject kobj;
+        /** Entry on the fuse_conn_list */
+        struct list_head entry;
+
+        /** Unique ID */
+        u64 id;
+
+        /** Dentries in the control filesystem */
+        struct dentry *ctl_dentry[FUSE_CTL_NUM_DENTRIES];
+
+        /** number of dentries used in the above array */
+        int ctl_ndents;
 
         /** O_ASYNC requests */
         struct fasync_struct *fasync;
@@ -327,11 +348,6 @@ static inline struct fuse_conn *get_fuse_conn(struct inode *inode)
         return get_fuse_conn_super(inode->i_sb);
 }
 
-static inline struct fuse_conn *get_fuse_conn_kobj(struct kobject *obj)
-{
-        return container_of(obj, struct fuse_conn, kobj);
-}
-
 static inline struct fuse_inode *get_fuse_inode(struct inode *inode)
 {
         return container_of(inode, struct fuse_inode, inode);
@@ -422,6 +438,9 @@ int fuse_dev_init(void);
  */
 void fuse_dev_cleanup(void);
 
+int fuse_ctl_init(void);
+void fuse_ctl_cleanup(void);
+
 /**
  * Allocate a request
  */
@@ -470,3 +489,23 @@ int fuse_do_getattr(struct inode *inode);
  * Invalidate inode attributes
  */
 void fuse_invalidate_attr(struct inode *inode);
+
+/**
+ * Acquire reference to fuse_conn
+ */
+struct fuse_conn *fuse_conn_get(struct fuse_conn *fc);
+
+/**
+ * Release reference to fuse_conn
+ */
+void fuse_conn_put(struct fuse_conn *fc);
+
+/**
+ * Add connection to control filesystem
+ */
+int fuse_ctl_add_conn(struct fuse_conn *fc);
+
+/**
+ * Remove connection from control filesystem
+ */
+void fuse_ctl_remove_conn(struct fuse_conn *fc);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 0225729977c4..13a7e8ab7a78 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -22,13 +22,8 @@ MODULE_DESCRIPTION("Filesystem in Userspace");
 MODULE_LICENSE("GPL");
 
 static kmem_cache_t *fuse_inode_cachep;
-static struct subsystem connections_subsys;
-
-struct fuse_conn_attr {
-        struct attribute attr;
-        ssize_t (*show)(struct fuse_conn *, char *);
-        ssize_t (*store)(struct fuse_conn *, const char *, size_t);
-};
+struct list_head fuse_conn_list;
+DEFINE_MUTEX(fuse_mutex);
 
 #define FUSE_SUPER_MAGIC 0x65735546
 
@@ -211,8 +206,11 @@ static void fuse_put_super(struct super_block *sb)
         kill_fasync(&fc->fasync, SIGIO, POLL_IN);
         wake_up_all(&fc->waitq);
         wake_up_all(&fc->blocked_waitq);
-        kobject_del(&fc->kobj);
-        kobject_put(&fc->kobj);
+        mutex_lock(&fuse_mutex);
+        list_del(&fc->entry);
+        fuse_ctl_remove_conn(fc);
+        mutex_unlock(&fuse_mutex);
+        fuse_conn_put(fc);
 }
 
 static void convert_fuse_statfs(struct kstatfs *stbuf, struct fuse_kstatfs *attr)
@@ -362,11 +360,6 @@ static int fuse_show_options(struct seq_file *m, struct vfsmount *mnt)
         return 0;
 }
 
-static void fuse_conn_release(struct kobject *kobj)
-{
-        kfree(get_fuse_conn_kobj(kobj));
-}
-
 static struct fuse_conn *new_conn(void)
 {
         struct fuse_conn *fc;
@@ -374,13 +367,12 @@ static struct fuse_conn *new_conn(void)
         fc = kzalloc(sizeof(*fc), GFP_KERNEL);
         if (fc) {
                 spin_lock_init(&fc->lock);
+                atomic_set(&fc->count, 1);
                 init_waitqueue_head(&fc->waitq);
                 init_waitqueue_head(&fc->blocked_waitq);
                 INIT_LIST_HEAD(&fc->pending);
                 INIT_LIST_HEAD(&fc->processing);
                 INIT_LIST_HEAD(&fc->io);
-                kobj_set_kset_s(fc, connections_subsys);
-                kobject_init(&fc->kobj);
                 atomic_set(&fc->num_waiting, 0);
                 fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
                 fc->bdi.unplug_io_fn = default_unplug_io_fn;
@@ -390,6 +382,18 @@ static struct fuse_conn *new_conn(void)
         return fc;
 }
 
+void fuse_conn_put(struct fuse_conn *fc)
+{
+        if (atomic_dec_and_test(&fc->count))
+                kfree(fc);
+}
+
+struct fuse_conn *fuse_conn_get(struct fuse_conn *fc)
+{
+        atomic_inc(&fc->count);
+        return fc;
+}
+
 static struct inode *get_root_inode(struct super_block *sb, unsigned mode)
 {
         struct fuse_attr attr;
@@ -459,10 +463,9 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
         request_send_background(fc, req);
 }
 
-static unsigned long long conn_id(void)
+static u64 conn_id(void)
 {
-        /* BKL is held for ->get_sb() */
-        static unsigned long long ctr = 1;
+        static u64 ctr = 1;
         return ctr++;
 }
 
@@ -519,24 +522,21 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
         if (!init_req)
                 goto err_put_root;
 
-        err = kobject_set_name(&fc->kobj, "%llu", conn_id());
-        if (err)
-                goto err_free_req;
-
-        err = kobject_add(&fc->kobj);
-        if (err)
-                goto err_free_req;
-
-        /* Setting file->private_data can't race with other mount()
-           instances, since BKL is held for ->get_sb() */
+        mutex_lock(&fuse_mutex);
         err = -EINVAL;
         if (file->private_data)
-                goto err_kobject_del;
+                goto err_unlock;
 
+        fc->id = conn_id();
+        err = fuse_ctl_add_conn(fc);
+        if (err)
+                goto err_unlock;
+
+        list_add_tail(&fc->entry, &fuse_conn_list);
         sb->s_root = root_dentry;
         fc->connected = 1;
-        kobject_get(&fc->kobj);
-        file->private_data = fc;
+        file->private_data = fuse_conn_get(fc);
+        mutex_unlock(&fuse_mutex);
         /*
          * atomic_dec_and_test() in fput() provides the necessary
          * memory barrier for file->private_data to be visible on all
@@ -548,15 +548,14 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 
         return 0;
 
- err_kobject_del:
-        kobject_del(&fc->kobj);
- err_free_req:
+ err_unlock:
+        mutex_unlock(&fuse_mutex);
         fuse_request_free(init_req);
  err_put_root:
         dput(root_dentry);
  err:
         fput(file);
-        kobject_put(&fc->kobj);
+        fuse_conn_put(fc);
         return err;
 }
 
@@ -574,68 +573,8 @@ static struct file_system_type fuse_fs_type = {
         .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 ssize_t fuse_conn_abort_store(struct fuse_conn *fc, const char *page,
-                                     size_t count)
-{
-        fuse_abort_conn(fc);
-        return count;
-}
-
-static struct fuse_conn_attr fuse_conn_waiting =
-        __ATTR(waiting, 0400, fuse_conn_waiting_show, NULL);
-static struct fuse_conn_attr fuse_conn_abort =
-        __ATTR(abort, 0600, NULL, fuse_conn_abort_store);
-
-static struct attribute *fuse_conn_attrs[] = {
-        &fuse_conn_waiting.attr,
-        &fuse_conn_abort.attr,
-        NULL,
-};
-
-static ssize_t fuse_conn_attr_show(struct kobject *kobj,
-                                   struct attribute *attr,
-                                   char *page)
-{
-        struct fuse_conn_attr *fca =
-                container_of(attr, struct fuse_conn_attr, attr);
-
-        if (fca->show)
-                return fca->show(get_fuse_conn_kobj(kobj), page);
-        else
-                return -EACCES;
-}
-
-static ssize_t fuse_conn_attr_store(struct kobject *kobj,
-                                    struct attribute *attr,
-                                    const char *page, size_t count)
-{
-        struct fuse_conn_attr *fca =
-                container_of(attr, struct fuse_conn_attr, attr);
-
-        if (fca->store)
-                return fca->store(get_fuse_conn_kobj(kobj), page, count);
-        else
-                return -EACCES;
-}
-
-static struct sysfs_ops fuse_conn_sysfs_ops = {
-        .show   = &fuse_conn_attr_show,
-        .store  = &fuse_conn_attr_store,
-};
-
-static struct kobj_type ktype_fuse_conn = {
-        .release        = fuse_conn_release,
-        .sysfs_ops      = &fuse_conn_sysfs_ops,
-        .default_attrs  = fuse_conn_attrs,
-};
-
 static decl_subsys(fuse, NULL, NULL);
-static decl_subsys(connections, &ktype_fuse_conn, NULL);
+static decl_subsys(connections, NULL, NULL);
 
 static void fuse_inode_init_once(void *foo, kmem_cache_t *cachep,
                                  unsigned long flags)
@@ -709,6 +648,7 @@ static int __init fuse_init(void)
         printk("fuse init (API version %i.%i)\n",
                FUSE_KERNEL_VERSION, FUSE_KERNEL_MINOR_VERSION);
 
+        INIT_LIST_HEAD(&fuse_conn_list);
         res = fuse_fs_init();
         if (res)
                 goto err;
@@ -721,8 +661,14 @@ static int __init fuse_init(void)
         if (res)
                 goto err_dev_cleanup;
 
+        res = fuse_ctl_init();
+        if (res)
+                goto err_sysfs_cleanup;
+
         return 0;
 
+ err_sysfs_cleanup:
+        fuse_sysfs_cleanup();
  err_dev_cleanup:
         fuse_dev_cleanup();
  err_fs_cleanup:
@@ -735,6 +681,7 @@ static void __exit fuse_exit(void)
 {
         printk(KERN_DEBUG "fuse exit\n");
 
+        fuse_ctl_cleanup();
         fuse_sysfs_cleanup();
         fuse_fs_cleanup();
         fuse_dev_cleanup();