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Subject[PATCH 15/22] sysfs: implement sysfs_dirent based link interface
Date
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sysfs_add_link() takes parent sd, name, mode and the target sd and
creates a link accordingly. Currently, sysfs links can only point to
directories but this limitiation is artificial to avoid inflating the
sysfs_dirent structure by one pointer with future changes and can be
easily removed.

Kobject based sysfs_create_link() is reimplemented using
sysfs_add_link().

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

Signed-off-by: Tejun Heo <htejun@gmail.com>
---
fs/sysfs/kobject.c | 47 +++++++++++++++++++++++++++
fs/sysfs/symlink.c | 83 +++++++++++++++++-------------------------------
include/linux/sysfs.h | 10 ++++++
3 files changed, 87 insertions(+), 53 deletions(-)
diff --git a/fs/sysfs/kobject.c b/fs/sysfs/kobject.c
index a34c54e..7400575 100644
--- a/fs/sysfs/kobject.c
+++ b/fs/sysfs/kobject.c
@@ -355,6 +355,53 @@ void sysfs_remove_bin_file(struct kobject * kobj, struct bin_attribute * attr)
}
EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);

+/*
+ * kobject link interface
+ */
+
+/**
+ * sysfs_create_link - create symlink between two objects.
+ * @kobj: object whose directory we're creating the link in.
+ * @target: object we're pointing to.
+ * @name: name of the symlink.
+ */
+int sysfs_create_link(struct kobject *kobj, struct kobject *target,
+ const char *name)
+{
+ struct sysfs_dirent *parent_sd, *target_sd, *sd;
+
+ BUG_ON(!name);
+
+ if (!kobj)
+ parent_sd = sysfs_root;
+ else
+ parent_sd = kobj->sd;
+
+ if (!parent_sd)
+ return -EFAULT;
+
+ /* target->sd can go away beneath us but is protected with
+ * sysfs_assoc_lock. Fetch target_sd from it.
+ */
+ spin_lock(&sysfs_assoc_lock);
+ target_sd = NULL;
+ if (target->sd)
+ target_sd = sysfs_get(target->sd);
+ spin_unlock(&sysfs_assoc_lock);
+
+ if (!target_sd)
+ return -ENOENT;
+
+ sd = sysfs_add_link(parent_sd, name, SYSFS_COPY_NAME, target_sd);
+
+ sysfs_put(target_sd);
+
+ if (IS_ERR(sd))
+ return PTR_ERR(sd);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(sysfs_create_link);
+
/**
* sysfs_remove_link - remove symlink in object's directory.
* @kobj: object we're acting for.
diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 2c3e4f7..42ecb69 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -5,7 +5,6 @@
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
-#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/mutex.h>

@@ -45,64 +44,45 @@ static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length)
}

/**
- * sysfs_create_link - create symlink between two objects.
- * @kobj: object whose directory we're creating the link in.
- * @target: object we're pointing to.
- * @name: name of the symlink.
+ * sysfs_add_link - add a new sysfs symlink
+ * @parent: sysfs_dirent to add symlink under
+ * @name: name of the symlink
+ * @mode: SYSFS_* flags for the new symlink
+ * @target: target of the symlink
+ *
+ * Add a new symlink which points to @target under @parent with
+ * the specified parameters.
+ *
+ * LOCKING:
+ * Kernel thread context (may sleep).
+ *
+ * RETURNS:
+ * Pointer to the new sysfs_dirent on success, ERR_PTR() value on
+ * error.
*/
-int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
+struct sysfs_dirent *sysfs_add_link(struct sysfs_dirent *parent,
+ const char *name, mode_t mode,
+ struct sysfs_dirent *target)
{
- struct sysfs_dirent *parent_sd = NULL;
- struct sysfs_dirent *target_sd = NULL;
- struct sysfs_dirent *sd = NULL;
- struct sysfs_addrm_cxt acxt;
- int error;
-
- BUG_ON(!name);
-
- if (!kobj)
- parent_sd = sysfs_root;
- else
- parent_sd = kobj->sd;
+ struct sysfs_dirent *sd;

- error = -EFAULT;
- if (!parent_sd)
- goto out_put;
-
- /* target->sd can go away beneath us but is protected with
- * sysfs_assoc_lock. Fetch target_sd from it.
+ /* Only symlink to directories are allowed. This is an
+ * artificial limitation. If ever needed, allowing symlinks
+ * to point to other types of sysfs nodes isn't difficult.
*/
- spin_lock(&sysfs_assoc_lock);
- if (target->sd)
- target_sd = sysfs_get(target->sd);
- spin_unlock(&sysfs_assoc_lock);
-
- error = -ENOENT;
- if (!target_sd)
- goto out_put;
+ if (sysfs_type(target) != SYSFS_DIR)
+ return ERR_PTR(-EINVAL);

- error = -ENOMEM;
- sd = sysfs_new_dirent(name, S_IRWXUGO | SYSFS_COPY_NAME, SYSFS_LINK);
+ /* allocate & initialize */
+ sd = sysfs_new_dirent(name, mode | S_IRWXUGO, SYSFS_LINK);
if (!sd)
- goto out_put;
-
- sd->s_link.target = target_sd;
- target_sd = NULL; /* reference is now owned by the symlink */
+ return ERR_PTR(-ENOMEM);

- sysfs_addrm_start(&acxt);
- error = sysfs_add_one(&acxt, parent_sd, sd);
- sysfs_addrm_finish(&acxt);
+ sd->s_link.target = sysfs_get(target);

- if (error)
- goto out_put;
-
- return 0;
-
- out_put:
- sysfs_put(target_sd);
- sysfs_put(sd);
- return error;
+ return sysfs_insert_one(parent, sd);
}
+EXPORT_SYMBOL_GPL(sysfs_add_link);

static int sysfs_get_target_path(struct sysfs_dirent * parent_sd,
struct sysfs_dirent * target_sd, char *path)
@@ -162,6 +142,3 @@ const struct inode_operations sysfs_link_inode_operations = {
.follow_link = sysfs_follow_link,
.put_link = sysfs_put_link,
};
-
-
-EXPORT_SYMBOL_GPL(sysfs_create_link);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index dfb6bd7..08ed1b0 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -60,6 +60,9 @@ struct sysfs_dirent *sysfs_add_file(struct sysfs_dirent *parent,
struct sysfs_dirent *sysfs_add_bin(struct sysfs_dirent *parent,
const char *name, mode_t mode, size_t size,
const struct sysfs_bin_ops *bops, void *data);
+struct sysfs_dirent *sysfs_add_link(struct sysfs_dirent *parent,
+ const char *name, mode_t mode,
+ struct sysfs_dirent *target);

struct sysfs_dirent *sysfs_find_child(struct sysfs_dirent *parent,
const char *name);
@@ -94,6 +97,13 @@ static inline struct sysfs_dirent *sysfs_add_bin(struct sysfs_dirent *parent,
return NULL;
}

+static inline struct sysfs_dirent *sysfs_add_link(struct sysfs_dirent *parent,
+ const char *name, mode_t mode,
+ struct sysfs_dirent *target)
+{
+ return NULL;
+}
+
static inline struct sysfs_dirent *sysfs_find_child(struct sysfs_dirent *parent,
const char *name)
{
--
1.5.0.3

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