linux-hardened/fs/sysfs/symlink.c
Tejun Heo fb6896da37 sysfs: restructure add/remove paths and fix inode update
The original add/remove code had the following problems.

* parent's timestamps are updated on dentry instantiation.  this is
  incorrect with reclaimable files.

* updating parent's timestamps isn't synchronized.

* parent nlink update assumes the inode is accessible which won't be
  true once directory dentries are made reclaimable.

This patch restructures add/remove paths to resolve the above
problems.  Add/removal are done in the following steps.

1. sysfs_addrm_start() : acquire locks including sysfs_mutex and other
   resources.

2-a. sysfs_add_one() : add new sd.  linking the new sd into the
     children list is caller's responsibility.

2-b. sysfs_remove_one() : remove a sd.  unlinking the sd from the
     children list is caller's responsibility.

3. sysfs_addrm_finish() : release all resources and clean up.

Steps 2-a and/or 2-b can be repeated multiple times.

Parent's inode is looked up during sysfs_addrm_start().  If available
(always at the moment), it's pinned and nlink is updated as sd's are
added and removed.  Timestamps are updated during finish if any sd has
been added or removed.  If parent's inode is not available during
start, sysfs_mutex ensures that parent inode is not created till
add/remove is complete.

All the complexity is contained inside the helper functions.
Especially, dentry/inode handling is properly hidden from the rest of
sysfs which now mostly operate on sysfs_dirents.  As an added bonus,
codes which use these helpers to add and remove sysfs_dirents are now
more structured and simpler.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2007-07-11 16:09:09 -07:00

182 lines
4 KiB
C

/*
* symlink.c - operations for sysfs symlinks.
*/
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <asm/semaphore.h>
#include "sysfs.h"
static int object_depth(struct sysfs_dirent *sd)
{
int depth = 0;
for (; sd->s_parent; sd = sd->s_parent)
depth++;
return depth;
}
static int object_path_length(struct sysfs_dirent * sd)
{
int length = 1;
for (; sd->s_parent; sd = sd->s_parent)
length += strlen(sd->s_name) + 1;
return length;
}
static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length)
{
--length;
for (; sd->s_parent; sd = sd->s_parent) {
int cur = strlen(sd->s_name);
/* back up enough to print this bus id with '/' */
length -= cur;
strncpy(buffer + length, sd->s_name, cur);
*(buffer + --length) = '/';
}
}
/**
* sysfs_create_link - create symlink between two objects.
* @kobj: object whose directory we're creating the link in.
* @target: object we're pointing to.
* @name: name of the symlink.
*/
int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
{
struct sysfs_dirent *parent_sd = NULL;
struct sysfs_dirent *target_sd = NULL;
struct sysfs_dirent *sd = NULL;
struct sysfs_addrm_cxt acxt;
int error;
BUG_ON(!name);
if (!kobj) {
if (sysfs_mount && sysfs_mount->mnt_sb)
parent_sd = sysfs_mount->mnt_sb->s_root->d_fsdata;
} else
parent_sd = kobj->sd;
error = -EFAULT;
if (!parent_sd)
goto out_put;
/* target->sd can go away beneath us but is protected with
* sysfs_assoc_lock. Fetch target_sd from it.
*/
spin_lock(&sysfs_assoc_lock);
if (target->sd)
target_sd = sysfs_get(target->sd);
spin_unlock(&sysfs_assoc_lock);
error = -ENOENT;
if (!target_sd)
goto out_put;
error = -ENOMEM;
sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
if (!sd)
goto out_put;
sd->s_elem.symlink.target_sd = target_sd;
sysfs_addrm_start(&acxt, parent_sd);
if (!sysfs_find_dirent(parent_sd, name)) {
sysfs_add_one(&acxt, sd);
sysfs_link_sibling(sd);
}
if (sysfs_addrm_finish(&acxt))
return 0;
error = -EEXIST;
/* fall through */
out_put:
sysfs_put(target_sd);
sysfs_put(sd);
return error;
}
/**
* sysfs_remove_link - remove symlink in object's directory.
* @kobj: object we're acting for.
* @name: name of the symlink to remove.
*/
void sysfs_remove_link(struct kobject * kobj, const char * name)
{
sysfs_hash_and_remove(kobj->sd, name);
}
static int sysfs_get_target_path(struct sysfs_dirent * parent_sd,
struct sysfs_dirent * target_sd, char *path)
{
char * s;
int depth, size;
depth = object_depth(parent_sd);
size = object_path_length(target_sd) + depth * 3 - 1;
if (size > PATH_MAX)
return -ENAMETOOLONG;
pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
for (s = path; depth--; s += 3)
strcpy(s,"../");
fill_object_path(target_sd, path, size);
pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
return 0;
}
static int sysfs_getlink(struct dentry *dentry, char * path)
{
struct sysfs_dirent *sd = dentry->d_fsdata;
struct sysfs_dirent *parent_sd = sd->s_parent;
struct sysfs_dirent *target_sd = sd->s_elem.symlink.target_sd;
int error;
mutex_lock(&sysfs_mutex);
error = sysfs_get_target_path(parent_sd, target_sd, path);
mutex_unlock(&sysfs_mutex);
return error;
}
static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
{
int error = -ENOMEM;
unsigned long page = get_zeroed_page(GFP_KERNEL);
if (page)
error = sysfs_getlink(dentry, (char *) page);
nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
return NULL;
}
static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
{
char *page = nd_get_link(nd);
if (!IS_ERR(page))
free_page((unsigned long)page);
}
const struct inode_operations sysfs_symlink_inode_operations = {
.readlink = generic_readlink,
.follow_link = sysfs_follow_link,
.put_link = sysfs_put_link,
};
EXPORT_SYMBOL_GPL(sysfs_create_link);
EXPORT_SYMBOL_GPL(sysfs_remove_link);