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Subject[PATCH 19/22] sysfs: implement sysfs_dirent based rename - sysfs_rename()
Date
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sysfs_rename() takes target @sd, @new_parent and @new_name and rename
@sd to @new_name and move it under @new_parent. @new_parent and/or
@new_name can be NULL if the specific operation is not needed.

To handle both move and rename && prepare for multiple renames in one
shot for easier symlink handling and shadow dirents, sysfs_rename() is
implemented to be able to handle arbitrary number of rename/move
operations.

During sysfs_prep_rename(), it acquires all the resources it will need
during the operations including dentries and copied names. After all
are acquired, all needed i_mutexes are locked. Deadlock is avoided by
using trylock. If any lock acquisition fails, it releases all
i_mutexes and retries after 1ms. Because i_mutexes are used very
lightly in sysfs, almost like spinlocks just to satisfy VFS locking
rules, I don't think there will be any starvation issues.

This makes rename a heavy operation but sysfs_rename() may fail and
it's shady-side-of-the-moon cold path where programming convenience
dominates performance by all measures.

sysfs_rename() can be called on any type of sysfs_dirent and always
copies @new_name.

Kobject based sysfs_rename_dir() and sysfs_move_dir() are
reimplemented using sysfs_remove().

This patch doesn't introduce any behavior change to the original API.

Signed-off-by: Tejun Heo <htejun@gmail.com>
---
fs/sysfs/dir.c | 433 +++++++++++++++++++++++++++++++++----------------
fs/sysfs/kobject.c | 31 ++++
include/linux/sysfs.h | 9 +
3 files changed, 337 insertions(+), 136 deletions(-)
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 986718c..d0eb9bf 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -11,6 +11,7 @@
#include <linux/idr.h>
#include <linux/completion.h>
#include <linux/mutex.h>
+#include <linux/delay.h>
#include "sysfs.h"

/* verify all mode flags are inside S_IFMT */
@@ -948,142 +949,6 @@ void sysfs_remove(struct sysfs_dirent *sd)
}
EXPORT_SYMBOL_GPL(sysfs_remove);

-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_op_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);
- 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;
-
- /* rename kobject and sysfs_dirent */
- error = -ENOMEM;
- new_name = dup_name = kstrdup(new_name, GFP_KERNEL);
- if (!new_name)
- goto out_unlock;
-
- error = kobject_set_name(kobj, "%s", new_name);
- if (error)
- goto out_unlock;
-
- 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:
- mutex_unlock(&sysfs_mutex);
- mutex_unlock(&parent->d_inode->i_mutex);
- kfree(dup_name);
- dput(old_dentry);
- dput(new_dentry);
- out:
- mutex_unlock(&sysfs_op_mutex);
- return error;
-}
-
-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_op_mutex);
- BUG_ON(!sd->s_parent);
- new_parent_sd = new_parent_kobj->sd ? new_parent_kobj->sd : sysfs_root;
-
- error = 0;
- 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);
- 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);
- 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);
- dput(new_dentry);
-
- /* Remove from old parent's list and insert into new parent's list. */
- sysfs_unlink_sibling(sd);
- sysfs_get(new_parent_sd);
- sysfs_put(sd->s_parent);
- sd->s_parent = new_parent_sd;
- sysfs_link_sibling(sd);
-
- out_unlock:
- 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_op_mutex);
- return error;
-}
-
/* Relationship between s_mode and the DT_xxx types */
static inline unsigned char dt_type(struct sysfs_dirent *sd)
{
@@ -1143,6 +1008,302 @@ const struct file_operations sysfs_dir_operations = {
.readdir = sysfs_readdir,
};

+/*
+ * Renaming a single node can result in renames of multiple nodes as
+ * symlinks pointing to the node are renamed together. To rename
+ * multiple nodes atogether atomically, all resources including
+ * i_mutexes and dentries are grabbed before committing the operation.
+ *
+ * i_mutexes are recorded using sysfs_rcxt_mutex_ent as they might not
+ * correspond one to one to renames (e.g. two symlinks to the same
+ * target in the same directory). All other resources are recorded in
+ * sysfs_rcxt_rename_ent. Both are chained to sysfs_rename_context to
+ * be used later.
+ */
+struct sysfs_rcxt_rename_ent {
+ struct list_head list;
+ struct sysfs_dirent *sd;
+ struct sysfs_dirent *new_parent;
+ const char *old_name;
+ const char *new_name;
+ int old_name_copied;
+ int new_name_copied;
+ struct dentry *old_dentry;
+ struct dentry *new_dentry;
+};
+
+struct sysfs_rcxt_mutex_ent {
+ struct list_head list;
+ struct mutex *mutex;
+ int locked;
+};
+
+struct sysfs_rename_context {
+ struct list_head mutexes;
+ struct list_head renames;
+};
+
+static struct sysfs_rcxt_rename_ent *
+sysfs_rcxt_add(struct sysfs_rename_context *rcxt, struct sysfs_dirent *sd,
+ struct sysfs_dirent *new_parent)
+{
+ struct sysfs_rcxt_rename_ent *rent;
+
+ rent = kzalloc(sizeof(*rent), GFP_KERNEL);
+ if (!rent)
+ return NULL;
+
+ rent->sd = sysfs_get(sd);
+ rent->new_parent = sysfs_get(new_parent);
+ rent->old_name = sd->s_name;
+ rent->old_name_copied = !!(sd->s_flags & SYSFS_FLAG_NAME_COPIED);
+
+ list_add_tail(&rent->list, &rcxt->renames);
+
+ return rent;
+}
+
+static int sysfs_rcxt_add_mutex(struct sysfs_rename_context *rcxt,
+ struct mutex *mutex)
+{
+ struct sysfs_rcxt_mutex_ent *ment;
+
+ list_for_each_entry(ment, &rcxt->mutexes, list)
+ if (ment->mutex == mutex)
+ return 0;
+
+ ment = kzalloc(sizeof(*ment), GFP_KERNEL);
+ if (!ment)
+ return -ENOMEM;
+
+ ment->mutex = mutex;
+
+ list_add_tail(&ment->list, &rcxt->mutexes);
+
+ return 0;
+}
+
+static int sysfs_rcxt_get_dentries(struct sysfs_rename_context *rcxt,
+ struct sysfs_rcxt_rename_ent *rent)
+{
+ struct dentry *old_dentry, *new_parent_dentry, *new_dentry;
+ int rc;
+
+ /* get old dentry */
+ old_dentry = sysfs_get_dentry(rent->sd);
+ if (IS_ERR(old_dentry))
+ return PTR_ERR(old_dentry);
+ rent->old_dentry = old_dentry;
+
+ /* allocate new dentry */
+ new_parent_dentry = sysfs_get_dentry(rent->new_parent);
+ if (IS_ERR(new_parent_dentry))
+ return PTR_ERR(new_parent_dentry);
+
+ new_dentry = d_alloc_name(new_parent_dentry, rent->new_name);
+ dput(new_parent_dentry);
+ if (!new_dentry)
+ return -ENOMEM;
+ rent->new_dentry = new_dentry;
+
+ /* add i_mutexes to mutex list */
+ rc = sysfs_rcxt_add_mutex(rcxt, &old_dentry->d_parent->d_inode->i_mutex);
+ if (rc)
+ return rc;
+
+ rc = sysfs_rcxt_add_mutex(rcxt, &new_dentry->d_parent->d_inode->i_mutex);
+ if (rc)
+ return rc;
+
+ return 0;
+}
+
+static void sysfs_post_rename(struct sysfs_rename_context *rcxt, int error)
+{
+ struct sysfs_rcxt_mutex_ent *ment, *next_ment;
+ struct sysfs_rcxt_rename_ent *rent, *next_rent;
+
+ /* release all mutexes */
+ list_for_each_entry_safe(ment, next_ment, &rcxt->mutexes, list) {
+ if (ment->locked)
+ mutex_unlock(ment->mutex);
+
+ list_del(&ment->list);
+ kfree(ment);
+ }
+
+ /* release all renames */
+ list_for_each_entry_safe(rent, next_rent, &rcxt->renames, list) {
+ /* If rename succeeded, old name is unused; otherwise,
+ * new name is unused. Free accordingly.
+ */
+ if (!error) {
+ if (rent->old_name_copied)
+ kfree(rent->old_name);
+ } else {
+ if (rent->new_name_copied)
+ kfree(rent->new_name);
+ }
+
+ dput(rent->old_dentry);
+ dput(rent->new_dentry);
+ sysfs_put(rent->sd);
+ sysfs_put(rent->new_parent);
+
+ list_del(&rent->list);
+ kfree(rent);
+ }
+}
+
+static int sysfs_prep_rename(struct sysfs_rename_context *rcxt,
+ struct sysfs_dirent *sd,
+ struct sysfs_dirent *new_parent,
+ const char *new_name)
+{
+ struct sysfs_rcxt_rename_ent *rent;
+ struct sysfs_rcxt_mutex_ent *ment;
+ int rc;
+
+ INIT_LIST_HEAD(&rcxt->mutexes);
+ INIT_LIST_HEAD(&rcxt->renames);
+
+ /*
+ * prep @sd
+ */
+ rc = -ENOMEM;
+ rent = sysfs_rcxt_add(rcxt, sd, new_parent);
+ if (!rent)
+ goto err;
+
+ rc = -ENOMEM;
+ rent->new_name = kstrdup(new_name, GFP_KERNEL);
+ if (!rent->new_name)
+ goto err;
+ rent->new_name_copied = 1;
+
+ rc = sysfs_rcxt_get_dentries(rcxt, rent);
+ if (rc)
+ goto err;
+
+ /*
+ * lock all i_mutexes
+ */
+ try_lock:
+ list_for_each_entry(ment, &rcxt->mutexes, list) {
+ if (!mutex_trylock(ment->mutex)) {
+ /* unlock all and retry */
+ list_for_each_entry(ment, &rcxt->mutexes, list) {
+ if (ment->locked) {
+ mutex_unlock(ment->mutex);
+ ment->locked = 0;
+ }
+ }
+
+ /* No need to be over-anxious, let's take it
+ * slow. Sysfs i_mutexes are lightly loaded
+ * and starvation is highly unlikely.
+ */
+ msleep(1);
+ goto try_lock;
+ }
+
+ ment->locked = 1;
+ }
+
+ return 0;
+
+ err:
+ sysfs_post_rename(rcxt, rc);
+ return rc;
+}
+
+/**
+ * sysfs_rename - rename and/or move sysfs node
+ * @sd: sysfs_dirent to rename
+ * @new_parent: new parent to move @sd under (NULL if only renaming)
+ * @new_name: new name to rename @sd to (NULL if only moving)
+ *
+ * Rename and/or move @sd. If both @new_parent and @new_name are
+ * specified, @sd is renamed to @new_name and moved under
+ * @new_parent atomically. If only one of the two is specified,
+ * only the specified operation is performed.
+ *
+ * Renaming and/or moving a sysfs node which is pointed to by
+ * symlinks causes the symlinks to be renamed according to their
+ * name formats.
+ *
+ * LOCKING:
+ * Kernel thread context (may sleep).
+ *
+ * RETURNS:
+ * 0 on success -errno on failure.
+ */
+int sysfs_rename(struct sysfs_dirent *sd, struct sysfs_dirent *new_parent,
+ const char *new_name)
+{
+ struct sysfs_rename_context rcxt;
+ struct sysfs_rcxt_rename_ent *rent;
+ int error;
+
+ mutex_lock(&sysfs_op_mutex);
+
+ if (!new_parent)
+ new_parent = sd->s_parent;
+ if (!new_name)
+ new_name = sd->s_name;
+
+ error = 0;
+ if (sd->s_parent == new_parent && !strcmp(sd->s_name, new_name))
+ goto out; /* nothing to rename */
+
+ error = sysfs_prep_rename(&rcxt, sd, new_parent, new_name);
+ if (error)
+ goto out;
+
+ /* check whether there are duplicate names */
+ error = -EEXIST;
+ list_for_each_entry(rent, &rcxt.renames, list)
+ if (sysfs_find_dirent(rent->new_parent, rent->new_name))
+ goto out_post;
+
+ mutex_lock(&sysfs_mutex);
+
+ /* rename sysfs_dirents and dentries */
+ list_for_each_entry(rent, &rcxt.renames, list) {
+ /* rename sd */
+ rent->sd->s_name = rent->new_name;
+ rent->sd->s_flags &= ~SYSFS_FLAG_NAME_COPIED;
+ if (rent->new_name_copied)
+ rent->sd->s_flags |= SYSFS_FLAG_NAME_COPIED;
+
+ /* move sd */
+ if (rent->sd->s_parent != rent->new_parent) {
+ sysfs_unlink_sibling(rent->sd);
+ sysfs_put(rent->sd->s_parent);
+ rent->sd->s_parent = sysfs_get(rent->new_parent);
+ sysfs_link_sibling(rent->sd);
+ }
+
+ /* update dcache and inode accordingly */
+ if (sysfs_type(rent->sd) == SYSFS_DIR) {
+ drop_nlink(rent->old_dentry->d_parent->d_inode);
+ inc_nlink(rent->new_dentry->d_parent->d_inode);
+ }
+ d_add(rent->new_dentry, NULL);
+ d_move(rent->old_dentry, rent->new_dentry);
+ }
+
+ mutex_unlock(&sysfs_mutex);
+ error = 0;
+ /* fall through */
+ out_post:
+ sysfs_post_rename(&rcxt, error);
+ out:
+ mutex_unlock(&sysfs_op_mutex);
+ return error;
+}
+EXPORT_SYMBOL_GPL(sysfs_rename);
+
/**
* sysfs_chmod - chmod a sysfs_dirent
* @sd: sysfs_dirent to chmod
diff --git a/fs/sysfs/kobject.c b/fs/sysfs/kobject.c
index 0a0d583..55b884b 100644
--- a/fs/sysfs/kobject.c
+++ b/fs/sysfs/kobject.c
@@ -75,6 +75,37 @@ void sysfs_remove_dir(struct kobject * kobj)
__sysfs_remove(sd, 0);
}

+int sysfs_rename_dir(struct kobject *kobj, const char *new_name)
+{
+ const char *dup_name;
+ int rc;
+
+ dup_name = kstrdup(new_name, GFP_KERNEL);
+ if (!dup_name)
+ return -ENOMEM;
+
+ rc = sysfs_rename(kobj->sd, NULL, new_name);
+ if (rc) {
+ kfree(dup_name);
+ return rc;
+ }
+
+ __kobject_set_name(kobj, dup_name);
+
+ return 0;
+}
+
+int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
+{
+ struct sysfs_dirent *sd = kobj->sd;
+ struct sysfs_dirent *new_parent_sd = new_parent_kobj->sd;
+
+ if (!new_parent_sd)
+ new_parent_sd = sysfs_root;
+
+ return sysfs_rename(sd, new_parent_sd, NULL);
+}
+
/*
* Subsystem file operations. These operations allow subsystems to
* have files that can be read/written.
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 08ed1b0..f0279a7 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -67,6 +67,8 @@ struct sysfs_dirent *sysfs_add_link(struct sysfs_dirent *parent,
struct sysfs_dirent *sysfs_find_child(struct sysfs_dirent *parent,
const char *name);
void sysfs_remove(struct sysfs_dirent *sd);
+int sysfs_rename(struct sysfs_dirent *sd, struct sysfs_dirent *new_parent,
+ const char *new_name);

void sysfs_notify_file(struct sysfs_dirent *sd);
int sysfs_chmod(struct sysfs_dirent *sd, mode_t mode);
@@ -114,6 +116,13 @@ static inline void sysfs_remove(struct sysfs_dirent *sd)
{
}

+static inline int sysfs_rename(struct sysfs_dirent *sd,
+ struct sysfs_dirent *new_parent,
+ const char *new_name)
+{
+ return 0;
+}
+
static inline void sysfs_notify_file(struct sysfs_dirent *sd)
{
}
--
1.5.0.3

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