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From 3b4d888114a5f6c1e848f892a2236db4ccf8345f Mon Sep 17 00:00:00 2001
From: Angelo Ruocco <angeloruocco90@gmail.com>
Date: Tue, 21 May 2019 10:01:54 +0200
Subject: [PATCH] cgroup: let a symlink too be created with a cftype file
This commit enables a cftype to have a symlink (of any name) that
points to the file associated with the cftype.
Signed-off-by: Angelo Ruocco <angeloruocco90@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit 54b7b868e826b294687c439b68ec55fe20cafe5b)
Signed-off-by: Li Yang <leoyang.li@nxp.com>
---
include/linux/cgroup-defs.h | 3 +++
kernel/cgroup/cgroup.c | 33 +++++++++++++++++++++++++++++----
2 files changed, 32 insertions(+), 4 deletions(-)
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -106,6 +106,8 @@ enum {
CFTYPE_WORLD_WRITABLE = (1 << 4), /* (DON'T USE FOR NEW FILES) S_IWUGO */
CFTYPE_DEBUG = (1 << 5), /* create when cgroup_debug */
+ CFTYPE_SYMLINKED = (1 << 6), /* pointed to by symlink too */
+
/* internal flags, do not use outside cgroup core proper */
__CFTYPE_ONLY_ON_DFL = (1 << 16), /* only on default hierarchy */
__CFTYPE_NOT_ON_DFL = (1 << 17), /* not on default hierarchy */
@@ -544,6 +546,7 @@ struct cftype {
* end of cftype array.
*/
char name[MAX_CFTYPE_NAME];
+ char link_name[MAX_CFTYPE_NAME];
unsigned long private;
/*
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1465,8 +1465,8 @@ struct cgroup *task_cgroup_from_root(str
static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
-static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
- char *buf)
+static char *cgroup_fill_name(struct cgroup *cgrp, const struct cftype *cft,
+ char *buf, bool write_link_name)
{
struct cgroup_subsys *ss = cft->ss;
@@ -1476,13 +1476,26 @@ static char *cgroup_file_name(struct cgr
snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
- cft->name);
+ write_link_name ? cft->link_name : cft->name);
} else {
- strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
+ strscpy(buf, write_link_name ? cft->link_name : cft->name,
+ CGROUP_FILE_NAME_MAX);
}
return buf;
}
+static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
+ char *buf)
+{
+ return cgroup_fill_name(cgrp, cft, buf, false);
+}
+
+static char *cgroup_link_name(struct cgroup *cgrp, const struct cftype *cft,
+ char *buf)
+{
+ return cgroup_fill_name(cgrp, cft, buf, true);
+}
+
/**
* cgroup_file_mode - deduce file mode of a control file
* @cft: the control file in question
@@ -1641,6 +1654,9 @@ static void cgroup_rm_file(struct cgroup
}
kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
+ if (cft->flags & CFTYPE_SYMLINKED)
+ kernfs_remove_by_name(cgrp->kn,
+ cgroup_link_name(cgrp, cft, name));
}
/**
@@ -3873,6 +3889,7 @@ static int cgroup_add_file(struct cgroup
{
char name[CGROUP_FILE_NAME_MAX];
struct kernfs_node *kn;
+ struct kernfs_node *kn_link;
struct lock_class_key *key = NULL;
int ret;
@@ -3903,6 +3920,14 @@ static int cgroup_add_file(struct cgroup
spin_unlock_irq(&cgroup_file_kn_lock);
}
+ if (cft->flags & CFTYPE_SYMLINKED) {
+ kn_link = kernfs_create_link(cgrp->kn,
+ cgroup_link_name(cgrp, cft, name),
+ kn);
+ if (IS_ERR(kn_link))
+ return PTR_ERR(kn_link);
+ }
+
return 0;
}
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