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Subject[PATCH 11/21] sysfs: add sysfs_dirent->s_parent
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Add sysfs_dirent->s_parent.  With this patch, each sd points to and
holds a reference to its parent. This allows walking sysfs tree
without referencing sd->s_dentry which can go away anytime if the user
doesn't control when it's deleted.

sd->s_parent is initialized and parent is referenced in
sysfs_attach_dirent(). Reference to parent is released when the sd is
released, so as long as reference to a sd is held, s_parent can be
followed.

dentry walk in sysfs_readdir() is convereted to s_parent walk.

This will be used to reimplement symlink such that it uses only
sysfs_dirent tree.

Signed-off-by: Tejun Heo <htejun@gmail.com>
---
fs/sysfs/dir.c | 30 +++++++++++++++++++++++-------
fs/sysfs/mount.c | 1 +
fs/sysfs/sysfs.h | 1 +
3 files changed, 25 insertions(+), 7 deletions(-)
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index a339e47..609a2f5 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -46,6 +46,11 @@ static void sysfs_free_ino(ino_t ino)

void release_sysfs_dirent(struct sysfs_dirent * sd)
{
+ struct sysfs_dirent *parent_sd;
+
+ repeat:
+ parent_sd = sd->s_parent;
+
if (sd->s_type & SYSFS_KOBJ_LINK) {
struct sysfs_symlink * sl = sd->s_element;
kfree(sl->link_name);
@@ -55,6 +60,10 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
kfree(sd->s_iattr);
sysfs_free_ino(sd->s_ino);
kmem_cache_free(sysfs_dir_cachep, sd);
+
+ sd = parent_sd;
+ if (sd && atomic_dec_and_test(&sd->s_count))
+ goto repeat;
}

static void sysfs_d_iput(struct dentry * dentry, struct inode * inode)
@@ -107,8 +116,10 @@ void sysfs_attach_dirent(struct sysfs_dirent *sd,
dentry->d_op = &sysfs_dentry_ops;
}

- if (parent_sd)
+ if (parent_sd) {
+ sd->s_parent = sysfs_get(parent_sd);
list_add(&sd->s_sibling, &parent_sd->s_children);
+ }
}

/*
@@ -553,7 +564,10 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
i++;
/* fallthrough */
case 1:
- ino = parent_ino(dentry);
+ if (parent_sd->s_parent)
+ ino = parent_sd->s_parent->s_ino;
+ else
+ ino = parent_sd->s_ino;
if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
break;
filp->f_pos++;
@@ -670,13 +684,13 @@ int sysfs_make_shadowed_dir(struct kobject *kobj,

struct dentry *sysfs_create_shadow_dir(struct kobject *kobj)
{
+ struct dentry *dir = kobj->dentry;
+ struct inode *inode = dir->d_inode;
+ struct dentry *parent = dir->d_parent;
+ struct sysfs_dirent *parent_sd = parent->d_fsdata;
+ struct dentry *shadow;
struct sysfs_dirent *sd;
- struct dentry *parent, *dir, *shadow;
- struct inode *inode;

- dir = kobj->dentry;
- inode = dir->d_inode;
- parent = dir->d_parent;
shadow = ERR_PTR(-EINVAL);
if (!sysfs_is_shadowed_inode(inode))
goto out;
@@ -688,6 +702,8 @@ struct dentry *sysfs_create_shadow_dir(struct kobject *kobj)
sd = sysfs_new_dirent(kobj, inode->i_mode, SYSFS_DIR);
if (!sd)
goto nomem;
+ /* point to parent_sd but don't attach to it */
+ sd->s_parent = sysfs_get(parent_sd);
sysfs_attach_dirent(sd, NULL, shadow);

d_instantiate(shadow, igrab(inode));
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index c1bafef..bc613f6 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -28,6 +28,7 @@ static const struct super_operations sysfs_ops = {
};

static struct sysfs_dirent sysfs_root = {
+ .s_count = ATOMIC_INIT(1),
.s_sibling = LIST_HEAD_INIT(sysfs_root.s_sibling),
.s_children = LIST_HEAD_INIT(sysfs_root.s_children),
.s_element = NULL,
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index c490156..0051ae2 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -1,5 +1,6 @@
struct sysfs_dirent {
atomic_t s_count;
+ struct sysfs_dirent * s_parent;
struct list_head s_sibling;
struct list_head s_children;
void * s_element;
--
1.5.0.3

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