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Subject[RFC v2 4/5] sysfs: add sysfs_add_group_link()
Date
The current __compat_only_sysfs_link_entry_to_kobj() code allows us to
create symbolic links in sysfs to groups or attributes. Something like:

/sys/.../entry1/groupA -> /sys/.../entry2/groupA

This patch extends this functionality with a new sysfs_add_group_link()
call that allows the link to have a different name than the group or
attribute, so:

/sys/.../entry1/link_name -> /sys/.../entry2/groupA

__compat_only_sysfs_link_entry_to_kobj() now just calls
sysfs_add_group_link(), passing in the same name for both the
group/attribute and for the link name.

This is needed by the ACPI HMAT enabling work because we want to have a
group of performance attributes that live in a memory target. This group
represents the performance between a memory target and its local
inititator. In the target the attribute group is named "local_init":

# tree mem_tgt2/local_init/
mem_tgt2/local_init/
├── mem_init0 -> ../../mem_init0
├── mem_tgt2 -> ../../mem_tgt2
├── read_bw_MBps
├── read_lat_nsec
├── write_bw_MBps
└── write_lat_nsec

We then want to link to this attribute group from the initiator, but change
the name of the link to "mem_tgtX" since we're now looking at it from the
initiator's perspective, and because a given initiator can have multiple
local memory targets:

# ls -l mem_init0/mem_tgt2
lrwxrwxrwx. 1 root root 0 Jul 5 14:38 mem_init0/mem_tgt2 ->
../mem_tgt2/local_init

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
fs/sysfs/group.c | 30 +++++++++++++++++++++++-------
include/linux/sysfs.h | 2 ++
2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index ac2de0e..19db57c8 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -367,15 +367,15 @@ void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
EXPORT_SYMBOL_GPL(sysfs_remove_link_from_group);

/**
- * __compat_only_sysfs_link_entry_to_kobj - add a symlink to a kobject pointing
- * to a group or an attribute
+ * sysfs_add_group_link - add a symlink to a kobject pointing to a group or
+ * an attribute
* @kobj: The kobject containing the group.
* @target_kobj: The target kobject.
* @target_name: The name of the target group or attribute.
+ * @link_name: The name of the link to the target group or attribute.
*/
-int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
- struct kobject *target_kobj,
- const char *target_name)
+int sysfs_add_group_link(struct kobject *kobj, struct kobject *target_kobj,
+ const char *target_name, const char *link_name)
{
struct kernfs_node *target;
struct kernfs_node *entry;
@@ -400,12 +400,28 @@ int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
return -ENOENT;
}

- link = kernfs_create_link(kobj->sd, target_name, entry);
+ link = kernfs_create_link(kobj->sd, link_name, entry);
if (IS_ERR(link) && PTR_ERR(link) == -EEXIST)
- sysfs_warn_dup(kobj->sd, target_name);
+ sysfs_warn_dup(kobj->sd, link_name);

kernfs_put(entry);
kernfs_put(target);
return IS_ERR(link) ? PTR_ERR(link) : 0;
}
+EXPORT_SYMBOL_GPL(sysfs_add_group_link);
+
+/**
+ * __compat_only_sysfs_link_entry_to_kobj - add a symlink to a kobject pointing
+ * to a group or an attribute
+ * @kobj: The kobject containing the group.
+ * @target_kobj: The target kobject.
+ * @target_name: The name of the target group or attribute.
+ */
+int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
+ struct kobject *target_kobj,
+ const char *target_name)
+{
+ return sysfs_add_group_link(kobj, target_kobj, target_name,
+ target_name);
+}
EXPORT_SYMBOL_GPL(__compat_only_sysfs_link_entry_to_kobj);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index c6f0f0d..865f499 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -278,6 +278,8 @@ int sysfs_add_link_to_group(struct kobject *kobj, const char *group_name,
struct kobject *target, const char *link_name);
void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
const char *link_name);
+int sysfs_add_group_link(struct kobject *kobj, struct kobject *target_kobj,
+ const char *target_name, const char *link_name);
int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
struct kobject *target_kobj,
const char *target_name);
--
2.9.4
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