Commit 2b29ac25 authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman
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sysfs: reimplement symlink using sysfs_dirent tree 

sysfs symlink is implemented by referencing dentry and kobject from
sysfs_dirent - symlink entry references kobject, dentry is used to
walk the tree.  This complicates object lifetimes rules and is
dangerous - for example, there is no way to tell to which module the
target of a symlink belongs and referencing that kobject can make it
linger after the module is gone.

This patch reimplements symlink using only sysfs_dirent tree.  sd for
a symlink points and holds reference to the target sysfs_dirent and
all walking is done using sysfs_dirent tree.  Simpler and safer.

Please read the following message for more info.

  http://article.gmane.org/gmane.linux.kernel/510293



Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent aecdceda

fs/sysfs/dir.c

+1 −1
Original line number Diff line number Diff line
@@ -54,7 +54,7 @@ void release_sysfs_dirent(struct sysfs_dirent * sd) 
	parent_sd = sd->s_parent;



	if (sd->s_type & SYSFS_KOBJ_LINK)

		kobject_put(sd->s_elem.symlink.target_kobj);

		sysfs_put(sd->s_elem.symlink.target_sd);

	if (sd->s_type & SYSFS_COPY_NAME)

		kfree(sd->s_name);

	kfree(sd->s_iattr);

fs/sysfs/symlink.c

+47 −41
Original line number Diff line number Diff line
@@ -11,50 +11,49 @@ 


#include "sysfs.h"



static int object_depth(struct kobject * kobj)

static int object_depth(struct sysfs_dirent *sd)

{

	struct kobject * p = kobj;

	int depth = 0;

	do { depth++; } while ((p = p->parent));



	for (; sd->s_parent; sd = sd->s_parent)

		depth++;



	return depth;

}



static int object_path_length(struct kobject * kobj)

static int object_path_length(struct sysfs_dirent * sd)

{

	struct kobject * p = kobj;

	int length = 1;

	do {

		length += strlen(kobject_name(p)) + 1;

		p = p->parent;

	} while (p);



	for (; sd->s_parent; sd = sd->s_parent)

		length += strlen(sd->s_name) + 1;



	return length;

}



static void fill_object_path(struct kobject * kobj, char * buffer, int length)

static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length)

{

	struct kobject * p;



	--length;

	for (p = kobj; p; p = p->parent) {

		int cur = strlen(kobject_name(p));

	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,kobject_name(p),cur);

		strncpy(buffer + length, sd->s_name, cur);

		*(buffer + --length) = '/';

	}

}



static int sysfs_add_link(struct dentry * parent, const char * name, struct kobject * target)

static int sysfs_add_link(struct sysfs_dirent * parent_sd, const char * name,

			  struct sysfs_dirent * target_sd)

{

	struct sysfs_dirent * parent_sd = parent->d_fsdata;

	struct sysfs_dirent * sd;



	sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);

	if (!sd)

		return -ENOMEM;



	sd->s_elem.symlink.target_kobj = kobject_get(target);

	sd->s_elem.symlink.target_sd = target_sd;

	sysfs_attach_dirent(sd, parent_sd, NULL);

	return 0;

}
@@ -68,6 +67,8 @@ static int sysfs_add_link(struct dentry * parent, const char * name, struct kobj 
int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)

{

	struct dentry *dentry = NULL;

	struct sysfs_dirent *parent_sd = NULL;

	struct sysfs_dirent *target_sd = NULL;

	int error = -EEXIST;



	BUG_ON(!name);
@@ -80,11 +81,27 @@ int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char 


	if (!dentry)

		return -EFAULT;

	parent_sd = dentry->d_fsdata;



	/* target->dentry can go away beneath us but is protected with

	 * kobj_sysfs_assoc_lock.  Fetch target_sd from it.

	 */

	spin_lock(&kobj_sysfs_assoc_lock);

	if (target->dentry)

		target_sd = sysfs_get(target->dentry->d_fsdata);

	spin_unlock(&kobj_sysfs_assoc_lock);



	if (!target_sd)

		return -ENOENT;



	mutex_lock(&dentry->d_inode->i_mutex);

	if (!sysfs_dirent_exist(dentry->d_fsdata, name))

		error = sysfs_add_link(dentry, name, target);

		error = sysfs_add_link(parent_sd, name, target_sd);

	mutex_unlock(&dentry->d_inode->i_mutex);



	if (error)

		sysfs_put(target_sd);



	return error;

}
@@ -100,14 +117,14 @@ void sysfs_remove_link(struct kobject * kobj, const char * name) 
	sysfs_hash_and_remove(kobj->dentry,name);

}



static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,

				 char *path)

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(kobj);

	size = object_path_length(target) + depth * 3 - 1;

	depth = object_depth(parent_sd);

	size = object_path_length(target_sd) + depth * 3 - 1;

	if (size > PATH_MAX)

		return -ENAMETOOLONG;
@@ -116,7 +133,7 @@ static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target, 
	for (s = path; depth--; s += 3)

		strcpy(s,"../");



	fill_object_path(target, path, size);

	fill_object_path(target_sd, path, size);

	pr_debug("%s: path = '%s'\n", __FUNCTION__, path);



	return 0;
@@ -124,27 +141,16 @@ static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target, 


static int sysfs_getlink(struct dentry *dentry, char * path)

{

	struct kobject *kobj, *target_kobj;

	int error = 0;



	kobj = sysfs_get_kobject(dentry->d_parent);

	if (!kobj)

		return -EINVAL;



	target_kobj = sysfs_get_kobject(dentry);

	if (!target_kobj) {

		kobject_put(kobj);

		return -EINVAL;

	}

	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;



	down_read(&sysfs_rename_sem);

	error = sysfs_get_target_path(kobj, target_kobj, path);

	error = sysfs_get_target_path(parent_sd, target_sd, path);

	up_read(&sysfs_rename_sem);



	kobject_put(kobj);

	kobject_put(target_kobj);

	return error;



}



static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)

fs/sysfs/sysfs.h

+5 −4
Original line number Diff line number Diff line
@@ -3,7 +3,7 @@ struct sysfs_elem_dir { 
};



struct sysfs_elem_symlink {

	struct kobject		* target_kobj;

	struct sysfs_dirent	* target_sd;

};



struct sysfs_elem_attr {
@@ -100,9 +100,10 @@ static inline struct kobject *sysfs_get_kobject(struct dentry *dentry) 
	spin_lock(&dcache_lock);

	if (!d_unhashed(dentry)) {

		struct sysfs_dirent * sd = dentry->d_fsdata;



		if (sd->s_type & SYSFS_KOBJ_LINK)

			kobj = kobject_get(sd->s_elem.symlink.target_kobj);

		else

			sd = sd->s_elem.symlink.target_sd;



		kobj = kobject_get(sd->s_elem.dir.kobj);

	}

	spin_unlock(&dcache_lock);

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