[PATCH 36/39] sysfs, kernfs: prepare mount path for kernfs

Tejun Heo
2013-11-03T09:55:05Z

We're in the process of separating out core sysfs functionality into
kernfs which will deal with sysfs_dirents directly. This patch
rearranges mount path so that the kernfs and sysfs parts are separate.

* As sysfs_super_info won't be visible outside kernfs proper,
kernfs_super_ns() is added to allow kernfs users to access a
super_block's namespace tag.

* Generic mount operation is separated out into kernfs_mount_ns().
sysfs_mount() now just performs sysfs-specific permission check,
acquires namespace tag, and invokes kernfs_mount_ns().

* Generic superblock release is separated out into kernfs_kill_sb()
which can be used directly as file_system_type->kill_sb(). As sysfs
needs to put the namespace tag, sysfs_kill_sb() wraps
kernfs_kill_sb() with ns tag put.

* sysfs_dir_cachep init and sysfs_inode_init() are separated out into
kernfs_init(). kernfs_init() uses only small amount of memory and
trying to handle and propagate kernfs_init() failure doesn't make
much sense. Use SLAB_PANIC for sysfs_dir_cachep and make
sysfs_inode_init() panic on failure.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
fs/kernfs/inode.c | 5 ++-
fs/kernfs/kernfs-internal.h | 2 +-
fs/namespace.c | 2 +
fs/sysfs/mount.c | 104 ++++++++++++++++++++++++++++++--------------
include/linux/kernfs.h | 28 ++++++++++++
5 files changed, 106 insertions(+), 35 deletions(-)

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index 9d4fab4..b4cae6f 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -37,9 +37,10 @@ static const struct inode_operations sysfs_inode_operations = {
.setxattr = sysfs_setxattr,
};

-int __init sysfs_inode_init(void)
+void __init sysfs_inode_init(void)
{
- return bdi_init(&sysfs_backing_dev_info);
+ if (bdi_init(&sysfs_backing_dev_info))
+ panic("failed to init sysfs_backing_dev_info");
}

static struct sysfs_inode_attrs *sysfs_init_inode_attrs(struct sysfs_dirent *sd)
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 584f169..943675e 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -144,7 +144,7 @@ int sysfs_getattr(struct vfsmount *mnt, struct dentry *dentry,
struct kstat *stat);
int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
size_t size, int flags);
-int sysfs_inode_init(void);
+void sysfs_inode_init(void);

/*
* dir.c
diff --git a/fs/namespace.c b/fs/namespace.c
index da5c494..40ffc2a1 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2787,6 +2787,8 @@ void __init mnt_init(void)

br_lock_init(&vfsmount_lock);

+ kernfs_init();
+
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index f143b20..5384732 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -86,18 +86,24 @@ static int sysfs_set_super(struct super_block *sb, void *data)
return error;
}

-static void free_sysfs_super_info(struct sysfs_super_info *info)
+/**
+ * kernfs_super_ns - determine the namespace tag of a kernfs super_block
+ * @sb: super_block of interest
+ *
+ * Return the namespace tag associated with kernfs super_block @sb.
+ */
+const void *kernfs_super_ns(struct super_block *sb)
{
- kobj_ns_drop(KOBJ_NS_TYPE_NET, (void *)info->ns);
- kfree(info);
+ struct sysfs_super_info *info = sysfs_info(sb);
+
+ return info->ns;
}

static struct dentry *sysfs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
- struct sysfs_super_info *info;
- struct super_block *sb;
- int error;
+ struct dentry *root;
+ void *ns;

if (!(flags & MS_KERNMOUNT)) {
if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
@@ -107,16 +113,44 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
return ERR_PTR(-EPERM);
}

+ ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
+ root = kernfs_mount_ns(fs_type, flags, sysfs_root, ns);
+ if (IS_ERR(root))
+ kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
+ return root;
+}
+
+/**
+ * kernfs_mount_ns - kernfs mount helper
+ * @fs_type: file_system_type of the fs being mounted
+ * @flags: mount flags specified for the mount
+ * @root: kernfs_root of the hierarchy being mounted
+ * @ns: optional namespace tag of the mount
+ *
+ * This is to be called from each kernfs user's file_system_type->mount()
+ * implementation, which should pass through the specified @fs_type and
+ * @flags, and specify the hierarchy and namespace tag to mount via @root
+ * and @ns, respectively.
+ *
+ * The return value can be passed to the vfs layer verbatim.
+ */
+struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
+ struct kernfs_root *root, const void *ns)
+{
+ struct super_block *sb;
+ struct sysfs_super_info *info;
+ int error;
+
info = kzalloc(sizeof(*info), GFP_KERNEL);
if (!info)
return ERR_PTR(-ENOMEM);

- info->root = sysfs_root;
- info->ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
+ info->root = root;
+ info->ns = ns;

sb = sget(fs_type, sysfs_test_super, sysfs_set_super, flags, info);
if (IS_ERR(sb) || sb->s_fs_info != info)
- free_sysfs_super_info(info);
+ kfree(info);
if (IS_ERR(sb))
return ERR_CAST(sb);
if (!sb->s_root) {
@@ -133,6 +167,20 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,

static void sysfs_kill_sb(struct super_block *sb)
{
+ kernfs_kill_sb(sb);
+ kobj_ns_drop(KOBJ_NS_TYPE_NET, (void *)kernfs_super_ns(sb));
+}
+
+/**
+ * kernfs_kill_sb - kill_sb for kernfs
+ * @sb: super_block being killed
+ *
+ * This can be used directly for file_system_type->kill_sb(). If a kernfs
+ * user needs extra cleanup, it can implement its own kill_sb() and call
+ * this function at the end.
+ */
+void kernfs_kill_sb(struct super_block *sb)
+{
struct sysfs_super_info *info = sysfs_info(sb);
struct sysfs_dirent *root_sd = sb->s_root->d_fsdata;

@@ -141,7 +189,7 @@ static void sysfs_kill_sb(struct super_block *sb)
* so we can't find it, before freeing sysfs_super_info.
*/
kill_anon_super(sb);
- free_sysfs_super_info(info);
+ kfree(info);
kernfs_put(root_sd);
}

@@ -152,37 +200,29 @@ static struct file_system_type sysfs_fs_type = {
.fs_flags = FS_USERNS_MOUNT,
};

-int __init sysfs_init(void)
+void __init kernfs_init(void)
{
- int err;
-
sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache",
sizeof(struct sysfs_dirent),
- 0, 0, NULL);
- if (!sysfs_dir_cachep)
- return -ENOMEM;
+ 0, SLAB_PANIC, NULL);
+ sysfs_inode_init();
+}

- err = sysfs_inode_init();
- if (err)
- goto out_err;
+int __init sysfs_init(void)
+{
+ int err;

sysfs_root = kernfs_create_root(NULL);
- if (IS_ERR(sysfs_root)) {
- err = PTR_ERR(sysfs_root);
- goto out_err;
- }
+ if (IS_ERR(sysfs_root))
+ return PTR_ERR(sysfs_root);
+
sysfs_root_sd = sysfs_root->sd;

err = register_filesystem(&sysfs_fs_type);
- if (err)
- goto out_destroy_root;
+ if (err) {
+ kernfs_destroy_root(sysfs_root);
+ return err;
+ }

return 0;
-
-out_destroy_root:
- kernfs_destroy_root(sysfs_root);
-out_err:
- kmem_cache_destroy(sysfs_dir_cachep);
- sysfs_dir_cachep = NULL;
- return err;
}
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b9ee397..403cbc5 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -18,6 +18,8 @@ struct file;
struct iattr;
struct seq_file;
struct vm_area_struct;
+struct super_block;
+struct file_system_type;

struct sysfs_dirent;

@@ -108,6 +110,13 @@ int kernfs_rename_ns(struct sysfs_dirent *sd, struct sysfs_dirent *new_parent,
int kernfs_setattr(struct sysfs_dirent *sd, const struct iattr *iattr);
void kernfs_notify(struct sysfs_dirent *sd);

+const void *kernfs_super_ns(struct super_block *sb);
+struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
+ struct kernfs_root *root, const void *ns);
+void kernfs_kill_sb(struct super_block *sb);
+
+void kernfs_init(void);
+
#else /* CONFIG_SYSFS */

static inline struct sysfs_dirent *
@@ -157,6 +166,18 @@ static inline int kernfs_setattr(struct sysfs_dirent *sd,

static inline void kernfs_notify(struct sysfs_dirent *sd) { }

+static inline const void *kernfs_super_ns(struct super_block *sb)
+{ return NULL; }
+
+static inline struct dentry *
+kernfs_mount_ns(struct file_system_type *fs_type, int flags,
+ struct kernfs_root *root, const void *ns)
+{ return ERR_PTR(-ENOSYS); }
+
+static inline void kernfs_kill_sb(struct super_block *sb) { }
+
+static inline void kernfs_init(void) { }
+
#endif /* CONFIG_SYSFS */

static inline struct sysfs_dirent *
@@ -198,4 +219,11 @@ static inline int kernfs_remove_by_name(struct sysfs_dirent *parent,
return kernfs_remove_by_name_ns(parent, name, NULL);
}

+static inline struct dentry *
+kernfs_mount(struct file_system_type *fs_type, int flags,
+ struct kernfs_root *root)
+{
+ return kernfs_mount_ns(fs_type, flags, root, NULL);
+}
+
#endif /* __LINUX_KERNFS_H */
--
1.8.3.1