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Subject[PATCH 12/15] sysfs: Propagate renames to the vfs on demand
Date
From: Eric W. Biederman <ebiederm@xmission.com>

By teaching sysfs_revalidate to hide a dentry for
a sysfs_dirent if the sysfs_dirent has been renamed,
and by teaching sysfs_lookup to return the original
dentry if the sysfs dirent has been renamed. I can
show the results of renames correctly without having to
update the dcache during the directory rename.

This massively simplifies the rename logic allowing a lot
of weird sysfs special cases to be removed along with
a lot of now unnecesary helper code.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
---
fs/namei.c | 22 -------
fs/sysfs/dir.c | 158 ++++++++++---------------------------------------
fs/sysfs/inode.c | 12 ----
fs/sysfs/sysfs.h | 1 -
include/linux/namei.h | 1 -
5 files changed, 32 insertions(+), 162 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index d11f404..d3c190c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1279,28 +1279,6 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
return __lookup_hash(&this, base, NULL);
}

-/**
- * lookup_one_noperm - bad hack for sysfs
- * @name: pathname component to lookup
- * @base: base directory to lookup from
- *
- * This is a variant of lookup_one_len that doesn't perform any permission
- * checks. It's a horrible hack to work around the braindead sysfs
- * architecture and should not be used anywhere else.
- *
- * DON'T USE THIS FUNCTION EVER, thanks.
- */
-struct dentry *lookup_one_noperm(const char *name, struct dentry *base)
-{
- int err;
- struct qstr this;
-
- err = __lookup_one_len(name, &this, base, strlen(name));
- if (err)
- return ERR_PTR(err);
- return __lookup_hash(&this, base, NULL);
-}
-
int user_path_at(int dfd, const char __user *name, unsigned flags,
struct path *path)
{
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index a05b027..0b60212 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -25,7 +25,6 @@
#include "sysfs.h"

DEFINE_MUTEX(sysfs_mutex);
-DEFINE_MUTEX(sysfs_rename_mutex);
DEFINE_SPINLOCK(sysfs_assoc_lock);

static DEFINE_SPINLOCK(sysfs_ino_lock);
@@ -85,46 +84,6 @@ static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
}

/**
- * sysfs_get_dentry - get dentry for the given sysfs_dirent
- * @sd: sysfs_dirent of interest
- *
- * Get dentry for @sd. Dentry is looked up if currently not
- * present. This function descends from the root looking up
- * dentry for each step.
- *
- * LOCKING:
- * mutex_lock(sysfs_rename_mutex)
- *
- * RETURNS:
- * Pointer to found dentry on success, ERR_PTR() value on error.
- */
-struct dentry *sysfs_get_dentry(struct sysfs_dirent *sd)
-{
- struct dentry *dentry = dget(sysfs_sb->s_root);
-
- while (dentry->d_fsdata != sd) {
- struct sysfs_dirent *cur;
- struct dentry *parent;
-
- /* find the first ancestor which hasn't been looked up */
- cur = sd;
- while (cur->s_parent != dentry->d_fsdata)
- cur = cur->s_parent;
-
- /* look it up */
- parent = dentry;
- mutex_lock(&parent->d_inode->i_mutex);
- dentry = lookup_one_noperm(cur->s_name, parent);
- mutex_unlock(&parent->d_inode->i_mutex);
- dput(parent);
-
- if (IS_ERR(dentry))
- break;
- }
- return dentry;
-}
-
-/**
* sysfs_get_active - get an active reference to sysfs_dirent
* @sd: sysfs_dirent to get an active reference to
*
@@ -315,6 +274,14 @@ static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
if (sd->s_flags & SYSFS_FLAG_REMOVED)
goto out_bad;

+ /* The sysfs dirent has been moved? */
+ if (dentry->d_parent->d_fsdata != sd->s_parent)
+ goto out_bad;
+
+ /* The sysfs dirent has been renamed */
+ if (strcmp(dentry->d_name.name, sd->s_name) != 0)
+ goto out_bad;
+
mutex_unlock(&sysfs_mutex);
out_valid:
return 1;
@@ -322,6 +289,12 @@ out_bad:
/* Remove the dentry from the dcache hashes.
* If this is a deleted dentry we use d_drop instead of d_delete
* so sysfs doesn't need to cope with negative dentries.
+ *
+ * If this is a dentry that has simply been renamed we
+ * use d_drop to remove it from the dcache lookup on its
+ * old parent. If this dentry persists later when a lookup
+ * is performed at its new name the dentry will be readded
+ * to the dcache hashes.
*/
is_dir = (sysfs_type(sd) == SYSFS_DIR);
mutex_unlock(&sysfs_mutex);
@@ -705,10 +678,15 @@ static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
}

/* instantiate and hash dentry */
- dentry->d_op = &sysfs_dentry_ops;
- dentry->d_fsdata = sysfs_get(sd);
- d_instantiate(dentry, inode);
- d_rehash(dentry);
+ ret = d_find_alias(inode);
+ if (!ret) {
+ dentry->d_op = &sysfs_dentry_ops;
+ dentry->d_fsdata = sysfs_get(sd);
+ d_add(dentry, inode);
+ } else {
+ d_move(ret, dentry);
+ iput(inode);
+ }

out_unlock:
mutex_unlock(&sysfs_mutex);
@@ -785,62 +763,32 @@ void sysfs_remove_dir(struct kobject * kobj)
int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
{
struct sysfs_dirent *sd = kobj->sd;
- struct dentry *parent = NULL;
- struct dentry *old_dentry = NULL, *new_dentry = NULL;
const char *dup_name = NULL;
int error;

- mutex_lock(&sysfs_rename_mutex);
+ mutex_lock(&sysfs_mutex);

error = 0;
if (strcmp(sd->s_name, new_name) == 0)
goto out; /* nothing to rename */

- /* get the original dentry */
- old_dentry = sysfs_get_dentry(sd);
- if (IS_ERR(old_dentry)) {
- error = PTR_ERR(old_dentry);
- old_dentry = NULL;
- goto out;
- }
-
- parent = old_dentry->d_parent;
-
- /* lock parent and get dentry for new name */
- mutex_lock(&parent->d_inode->i_mutex);
- mutex_lock(&sysfs_mutex);
-
error = -EEXIST;
if (sysfs_find_dirent(sd->s_parent, new_name))
- goto out_unlock;
-
- error = -ENOMEM;
- new_dentry = d_alloc_name(parent, new_name);
- if (!new_dentry)
- goto out_unlock;
+ goto out;

/* rename sysfs_dirent */
error = -ENOMEM;
new_name = dup_name = kstrdup(new_name, GFP_KERNEL);
if (!new_name)
- goto out_unlock;
+ goto out;

dup_name = sd->s_name;
sd->s_name = new_name;

- /* rename */
- d_add(new_dentry, NULL);
- d_move(old_dentry, new_dentry);
-
error = 0;
- out_unlock:
+ out:
mutex_unlock(&sysfs_mutex);
- mutex_unlock(&parent->d_inode->i_mutex);
kfree(dup_name);
- dput(old_dentry);
- dput(new_dentry);
- out:
- mutex_unlock(&sysfs_rename_mutex);
return error;
}

@@ -848,12 +796,11 @@ int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
{
struct sysfs_dirent *sd = kobj->sd;
struct sysfs_dirent *new_parent_sd;
- struct dentry *old_parent, *new_parent = NULL;
- struct dentry *old_dentry = NULL, *new_dentry = NULL;
int error;

- mutex_lock(&sysfs_rename_mutex);
BUG_ON(!sd->s_parent);
+
+ mutex_lock(&sysfs_mutex);
new_parent_sd = (new_parent_kobj && new_parent_kobj->sd) ?
new_parent_kobj->sd : &sysfs_root;

@@ -861,61 +808,20 @@ int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
if (sd->s_parent == new_parent_sd)
goto out; /* nothing to move */

- /* get dentries */
- old_dentry = sysfs_get_dentry(sd);
- if (IS_ERR(old_dentry)) {
- error = PTR_ERR(old_dentry);
- old_dentry = NULL;
- goto out;
- }
- old_parent = old_dentry->d_parent;
-
- new_parent = sysfs_get_dentry(new_parent_sd);
- if (IS_ERR(new_parent)) {
- error = PTR_ERR(new_parent);
- new_parent = NULL;
- goto out;
- }
-
-again:
- mutex_lock(&old_parent->d_inode->i_mutex);
- if (!mutex_trylock(&new_parent->d_inode->i_mutex)) {
- mutex_unlock(&old_parent->d_inode->i_mutex);
- goto again;
- }
- mutex_lock(&sysfs_mutex);
-
error = -EEXIST;
if (sysfs_find_dirent(new_parent_sd, sd->s_name))
- goto out_unlock;
-
- error = -ENOMEM;
- new_dentry = d_alloc_name(new_parent, sd->s_name);
- if (!new_dentry)
- goto out_unlock;
-
- error = 0;
- d_add(new_dentry, NULL);
- d_move(old_dentry, new_dentry);
+ goto out;

/* Remove from old parent's list and insert into new parent's list. */
sysfs_unlink_sibling(sd);
sysfs_get(new_parent_sd);
- drop_nlink(old_parent->d_inode);
sysfs_put(sd->s_parent);
sd->s_parent = new_parent_sd;
- inc_nlink(new_parent->d_inode);
sysfs_link_sibling(sd);

- out_unlock:
+ error = 0;
+out:
mutex_unlock(&sysfs_mutex);
- mutex_unlock(&new_parent->d_inode->i_mutex);
- mutex_unlock(&old_parent->d_inode->i_mutex);
- out:
- dput(new_parent);
- dput(old_dentry);
- dput(new_dentry);
- mutex_unlock(&sysfs_rename_mutex);
return error;
}

diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 2dcafe8..082a3eb 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -205,17 +205,6 @@ static inline void set_inode_attr(struct inode * inode, struct iattr * iattr)
inode->i_ctime = iattr->ia_ctime;
}

-
-/*
- * sysfs has a different i_mutex lock order behavior for i_mutex than other
- * filesystems; sysfs i_mutex is called in many places with subsystem locks
- * held. At the same time, many of the VFS locking rules do not apply to
- * sysfs at all (cross directory rename for example). To untangle this mess
- * (which gives false positives in lockdep), we're giving sysfs inodes their
- * own class for i_mutex.
- */
-static struct lock_class_key sysfs_inode_imutex_key;
-
static int sysfs_count_nlink(struct sysfs_dirent *sd)
{
struct sysfs_dirent *child;
@@ -268,7 +257,6 @@ static void sysfs_init_inode(struct sysfs_dirent *sd, struct inode *inode)
inode->i_mapping->a_ops = &sysfs_aops;
inode->i_mapping->backing_dev_info = &sysfs_backing_dev_info;
inode->i_op = &sysfs_inode_operations;
- lockdep_set_class(&inode->i_mutex, &sysfs_inode_imutex_key);

set_default_inode_attr(inode, sd->s_mode);
sysfs_refresh_inode(sd, inode);
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 90b3501..98a15bf 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -103,7 +103,6 @@ extern struct kmem_cache *sysfs_dir_cachep;
* dir.c
*/
extern struct mutex sysfs_mutex;
-extern struct mutex sysfs_rename_mutex;
extern spinlock_t sysfs_assoc_lock;

extern const struct file_operations sysfs_dir_operations;
diff --git a/include/linux/namei.h b/include/linux/namei.h
index ec0f607..0289467 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -76,7 +76,6 @@ extern struct file *nameidata_to_filp(struct nameidata *nd, int flags);
extern void release_open_intent(struct nameidata *);

extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
-extern struct dentry *lookup_one_noperm(const char *, struct dentry *);

extern int follow_down(struct path *);
extern int follow_up(struct path *);
--
1.6.5.2.143.g8cc62


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