path: root/fs/kernfs/dir.c

/*
 * fs/kernfs/dir.c - kernfs directory implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
 *
 * This file is released under the GPLv2.
 */

#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/idr.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/hash.h>

#include "kernfs-internal.h"

DEFINE_MUTEX(kernfs_mutex);
static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by rename_lock */

#define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)

static bool kernfs_active(struct kernfs_node *kn)
{
	lockdep_assert_held(&kernfs_mutex);
	return atomic_read(&kn->active) >= 0;
}

static bool kernfs_lockdep(struct kernfs_node *kn)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	return kn->flags & KERNFS_LOCKDEP;
#else
	return false;
#endif
}

static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
{
	return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
}

/* kernfs_node_depth - compute depth from @from to @to */
static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)
{
	size_t depth = 0;

	while (to->parent && to != from) {
		depth++;
		to = to->parent;
	}
	return depth;
}

static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
						  struct kernfs_node *b)
{
	size_t da, db;
	struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);

	if (ra != rb)
		return NULL;

	da = kernfs_depth(ra->kn, a);
	db = kernfs_depth(rb->kn, b);

	while (da > db) {
		a = a->parent;
		da--;
	}
	while (db > da) {
		b = b->parent;
		db--;
	}

	/* worst case b and a will be the same at root */
	while (b != a) {
		b = b->parent;
		a = a->parent;
	}

	return a;
}

/**
 * kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
 * where kn_from is treated as root of the path.
 * @kn_from: kernfs node which should be treated as root for the path
 * @kn_to: kernfs node to which path is needed
 * @buf: buffer to copy the path into
 * @buflen: size of @buf
 *
 * We need to handle couple of scenarios here:
 * [1] when @kn_from is an ancestor of @kn_to at some level
 * kn_from: /n1/n2/n3
 * kn_to:   /n1/n2/n3/n4/n5
 * result:  /n4/n5
 *
 * [2] when @kn_from is on a different hierarchy and we need to find common
 * ancestor between @kn_from and @kn_to.
 * kn_from: /n1/n2/n3/n4
 * kn_to:   /n1/n2/n5
 * result:  /../../n5
 * OR
 * kn_from: /n1/n2/n3/n4/n5   [depth=5]
 * kn_to:   /n1/n2/n3         [depth=3]
 * result:  /../..
 *
 * Returns the length of the full path.  If the full length is equal to or
 * greater than @buflen, @buf contains the truncated path with the trailing
 * '\0'.  On error, -errno is returned.
 */
static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
					struct kernfs_node *kn_from,
					char *buf, size_t buflen)
{
	struct kernfs_node *kn, *common;
	const char parent_str[] = "/..";
	size_t depth_from, depth_to, len = 0;
	int i, j;

	if (!kn_from)
		kn_from = kernfs_root(kn_to)->kn;

	if (kn_from == kn_to)
		return strlcpy(buf, "/", buflen);

	common = kernfs_common_ancestor(kn_from, kn_to);
	if (WARN_ON(!common))
		return -EINVAL;

	depth_to = kernfs_depth(common, kn_to);
	depth_from = kernfs_depth(common, kn_from);

	if (buf)
		buf[0] = '\0';

	for (i = 0; i < depth_from; i++)
		len += strlcpy(buf + len, parent_str,
			       len < buflen ? buflen - len : 0);

	/* Calculate how many bytes we need for the rest */
	for (i = depth_to - 1; i >= 0; i--) {
		for (kn = kn_to, j = 0; j < i; j++)
			kn = kn->parent;
		len += strlcpy(buf + len, "/",
			       len < buflen ? buflen - len : 0);
		len += strlcpy(buf + len, kn->name,
			       len < buflen ? buflen - len : 0);
	}

	return len;
}

/**
 * kernfs_name - obtain the name of a given node
 * @kn: kernfs_node of interest
 * @buf: buffer to copy @kn's name into
 * @buflen: size of @buf
 *
 * Copies the name of @kn into @buf of @buflen bytes.  The behavior is
 * similar to strlcpy().  It returns the length of @kn's name and if @buf
 * isn't long enough, it's filled upto @buflen-1 and nul terminated.
 *
 * This function can be called from any context.
 */
int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
{
	unsigned long flags;
	int ret;

	spin_lock_irqsave(&kernfs_rename_lock, flags);
	ret = kernfs_name_locked(kn, buf, buflen);
	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
	return ret;
}

/**
 * kernfs_path_from_node - build path of node @to relative to @from.
 * @from: parent kernfs_node relative to which we need to build the path
 * @to: kernfs_node of interest
 * @buf: buffer to copy @to's path into
 * @buflen: size of @buf
 *
 * Builds @to's path relative to @from in @buf. @fro