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: Tejun Heo <htejun@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Tejun Heo
Greg Kroah-Hartman
parent
aecdcedaab
commit
2b29ac252a
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@ -54,7 +54,7 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
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parent_sd = sd->s_parent;
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if (sd->s_type & SYSFS_KOBJ_LINK)
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kobject_put(sd->s_elem.symlink.target_kobj);
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sysfs_put(sd->s_elem.symlink.target_sd);
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if (sd->s_type & SYSFS_COPY_NAME)
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kfree(sd->s_name);
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kfree(sd->s_iattr);
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@ -11,50 +11,49 @@
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#include "sysfs.h"
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static int object_depth(struct kobject * kobj)
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static int object_depth(struct sysfs_dirent *sd)
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{
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struct kobject * p = kobj;
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int depth = 0;
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do { depth++; } while ((p = p->parent));
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for (; sd->s_parent; sd = sd->s_parent)
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depth++;
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return depth;
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}
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static int object_path_length(struct kobject * kobj)
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static int object_path_length(struct sysfs_dirent * sd)
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{
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struct kobject * p = kobj;
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int length = 1;
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do {
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length += strlen(kobject_name(p)) + 1;
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p = p->parent;
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} while (p);
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for (; sd->s_parent; sd = sd->s_parent)
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length += strlen(sd->s_name) + 1;
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return length;
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}
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static void fill_object_path(struct kobject * kobj, char * buffer, int length)
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static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length)
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{
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struct kobject * p;
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--length;
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for (p = kobj; p; p = p->parent) {
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int cur = strlen(kobject_name(p));
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for (; sd->s_parent; sd = sd->s_parent) {
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int cur = strlen(sd->s_name);
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/* back up enough to print this bus id with '/' */
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length -= cur;
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strncpy(buffer + length,kobject_name(p),cur);
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strncpy(buffer + length, sd->s_name, cur);
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*(buffer + --length) = '/';
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}
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}
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static int sysfs_add_link(struct dentry * parent, const char * name, struct kobject * target)
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static int sysfs_add_link(struct sysfs_dirent * parent_sd, const char * name,
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struct sysfs_dirent * target_sd)
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{
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struct sysfs_dirent * parent_sd = parent->d_fsdata;
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struct sysfs_dirent * sd;
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sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
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if (!sd)
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return -ENOMEM;
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sd->s_elem.symlink.target_kobj = kobject_get(target);
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sd->s_elem.symlink.target_sd = target_sd;
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sysfs_attach_dirent(sd, parent_sd, NULL);
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return 0;
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}
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@ -68,6 +67,8 @@ static int sysfs_add_link(struct dentry * parent, const char * name, struct kobj
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int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
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{
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struct dentry *dentry = NULL;
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struct sysfs_dirent *parent_sd = NULL;
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struct sysfs_dirent *target_sd = NULL;
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int error = -EEXIST;
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BUG_ON(!name);
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@ -80,11 +81,27 @@ int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char
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if (!dentry)
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return -EFAULT;
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parent_sd = dentry->d_fsdata;
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/* target->dentry can go away beneath us but is protected with
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* kobj_sysfs_assoc_lock. Fetch target_sd from it.
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*/
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spin_lock(&kobj_sysfs_assoc_lock);
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if (target->dentry)
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target_sd = sysfs_get(target->dentry->d_fsdata);
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spin_unlock(&kobj_sysfs_assoc_lock);
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if (!target_sd)
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return -ENOENT;
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mutex_lock(&dentry->d_inode->i_mutex);
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if (!sysfs_dirent_exist(dentry->d_fsdata, name))
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error = sysfs_add_link(dentry, name, target);
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error = sysfs_add_link(parent_sd, name, target_sd);
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mutex_unlock(&dentry->d_inode->i_mutex);
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if (error)
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sysfs_put(target_sd);
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return error;
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}
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@ -100,14 +117,14 @@ void sysfs_remove_link(struct kobject * kobj, const char * name)
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sysfs_hash_and_remove(kobj->dentry,name);
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}
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static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
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char *path)
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static int sysfs_get_target_path(struct sysfs_dirent * parent_sd,
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struct sysfs_dirent * target_sd, char *path)
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{
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char * s;
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int depth, size;
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depth = object_depth(kobj);
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size = object_path_length(target) + depth * 3 - 1;
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depth = object_depth(parent_sd);
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size = object_path_length(target_sd) + depth * 3 - 1;
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if (size > PATH_MAX)
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return -ENAMETOOLONG;
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@ -116,7 +133,7 @@ static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
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for (s = path; depth--; s += 3)
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strcpy(s,"../");
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fill_object_path(target, path, size);
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fill_object_path(target_sd, path, size);
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pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
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return 0;
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@ -124,27 +141,16 @@ static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
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static int sysfs_getlink(struct dentry *dentry, char * path)
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{
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struct kobject *kobj, *target_kobj;
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int error = 0;
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kobj = sysfs_get_kobject(dentry->d_parent);
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if (!kobj)
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return -EINVAL;
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target_kobj = sysfs_get_kobject(dentry);
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if (!target_kobj) {
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kobject_put(kobj);
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return -EINVAL;
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}
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struct sysfs_dirent *sd = dentry->d_fsdata;
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struct sysfs_dirent *parent_sd = sd->s_parent;
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struct sysfs_dirent *target_sd = sd->s_elem.symlink.target_sd;
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int error;
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down_read(&sysfs_rename_sem);
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error = sysfs_get_target_path(kobj, target_kobj, path);
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error = sysfs_get_target_path(parent_sd, target_sd, path);
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up_read(&sysfs_rename_sem);
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kobject_put(kobj);
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kobject_put(target_kobj);
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return error;
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return error;
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}
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static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
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@ -3,7 +3,7 @@ struct sysfs_elem_dir {
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};
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struct sysfs_elem_symlink {
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struct kobject * target_kobj;
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struct sysfs_dirent * target_sd;
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};
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struct sysfs_elem_attr {
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@ -100,10 +100,11 @@ static inline struct kobject *sysfs_get_kobject(struct dentry *dentry)
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spin_lock(&dcache_lock);
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if (!d_unhashed(dentry)) {
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struct sysfs_dirent * sd = dentry->d_fsdata;
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if (sd->s_type & SYSFS_KOBJ_LINK)
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kobj = kobject_get(sd->s_elem.symlink.target_kobj);
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else
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kobj = kobject_get(sd->s_elem.dir.kobj);
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sd = sd->s_elem.symlink.target_sd;
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kobj = kobject_get(sd->s_elem.dir.kobj);
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}
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spin_unlock(&dcache_lock);
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