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sysfs, kernfs: implement kernfs_create/destroy_root()

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There currently is single kernfs hierarchy in the whole system which
is used for sysfs.  kernfs needs to support multiple hierarchies to
allow other users.  This patch introduces struct kernfs_root which
serves as the root of each kernfs hierarchy and implements
kernfs_create/destroy_root().

* Each kernfs_root is associated with a root sd (sysfs_dentry).  The
  root is freed when the root sd is released and kernfs_destory_root()
  simply invokes kernfs_remove() on the root sd.  sysfs_remove_one()
  is updated to handle release of the root sd.  Note that ps_iattr
  update in sysfs_remove_one() is trivially updated for readability.

* Root sd's are now dynamically allocated using sysfs_new_dirent().
  Update sysfs_alloc_ino() so that it gives out ino from 1 so that the
  root sd still gets ino 1.

* While kernfs currently only points to the root sd, it'll soon grow
  fields which are specific to each hierarchy.  As determining a given
  sd's root will be necessary, sd->s_dir.root is added.  This backlink
  fits better as a separate field in sd; however, sd->s_dir is inside
  union with space to spare, so use it to save space and provide
  kernfs_root() accessor to determine the root sd.

* As hierarchies may be destroyed now, each mount needs to hold onto
  the hierarchy it's attached to.  Update sysfs_fill_super() and
  sysfs_kill_sb() so that they get and put the kernfs_root
  respectively.

* sysfs_root is replaced with kernfs_root which is dynamically created
  by invoking kernfs_create_root() from sysfs_init().

This patch doesn't introduce any visible behavior changes.

v2: kernfs_create_root() forgot to set @sd->priv.  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tejun Heo
2013-11-28 14:54:40 -05:00
committed by Greg Kroah-Hartman
parent 061447a496
commit ba7443bc65
4 changed files with 113 additions and 20 deletions
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20
fs/kernfs/kernfs-internal.h
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@@ -25,6 +25,12 @@ struct sysfs_elem_dir {
unsigned long subdirs;
/* children rbtree starts here and goes through sd->s_rb */
struct rb_root children;
/*
* The kernfs hierarchy this directory belongs to. This fits
* better directly in sysfs_dirent but is here to save space.
*/
struct kernfs_root *root;
};
struct sysfs_elem_symlink {
@@ -104,6 +110,20 @@ static inline unsigned int sysfs_type(struct sysfs_dirent *sd)
return sd->s_flags & SYSFS_TYPE_MASK;
}
/**
* kernfs_root - find out the kernfs_root a sysfs_dirent belongs to
* @sd: sysfs_dirent of interest
*
* Return the kernfs_root @sd belongs to.
*/
static inline struct kernfs_root *kernfs_root(struct sysfs_dirent *sd)
{
/* if parent exists, it's always a dir; otherwise, @sd is a dir */
if (sd->s_parent)
sd = sd->s_parent;
return sd->s_dir.root;
}
/*
* Context structure to be used while adding/removing nodes.
*/