Commit 4b93dc9b authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman

sysfs, kernfs: prepare mount path for kernfs

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.

  After this change, kernfs_init() should be called before
  sysfs_init(), fs/namespace.c::mnt_init() modified accordingly.
Signed-off-by: default avatarTejun Heo <>
Cc: Christoph Hellwig <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent df394fb5
......@@ -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)
......@@ -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
......@@ -2790,6 +2790,8 @@ void __init mnt_init(void)
for (u = 0; u < HASH_SIZE; u++)
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
......@@ -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);
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)
if (IS_ERR(sb))
return ERR_CAST(sb);
if (!sb->s_root) {
......@@ -132,6 +166,20 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
static void sysfs_kill_sb(struct super_block *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.
......@@ -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;
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;
return 0;
if (err) {
sysfs_dir_cachep = NULL;
return err;
return 0;
......@@ -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;
......@@ -109,6 +111,13 @@ void kernfs_enable_ns(struct sysfs_dirent *sd);
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 *
......@@ -160,6 +169,18 @@ 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 *
......@@ -201,4 +222,11 @@ 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 */
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