Commit 2b29ac25 authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman

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/510293Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent aecdceda
......@@ -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);
......
......@@ -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)
......
......@@ -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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