[PATCH 4/5] cgroup: convert "tasks" and "cgroup.procs" handle to use cftype->write()

Tejun Heo
2014-05-06T12:45:30Z

cgroup_tasks_write() and cgroup_procs_write() are currently using
cftype->write_u64(). This patch converts them to use cftype->write()
instead. This allows access to the associated kernfs_open_file which
will be necessary to implement the planned kernfs active protection
manipulation for these files.

This shifts buffer parsing to attach_task_by_pid() and makes it return
@nbytes on success. Let's rename it to __cgroup_procs_write() to
clearly indicate that this is a write handler implementation.

This patch doesn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/cgroup.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4b340c3..06ad484 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2232,12 +2232,18 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
* function to attach either it or all tasks in its threadgroup. Will lock
* cgroup_mutex and threadgroup.
*/
-static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
+static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
+ size_t nbytes, loff_t off, bool threadgroup)
{
struct task_struct *tsk;
const struct cred *cred = current_cred(), *tcred;
+ struct cgroup *cgrp = of_css(of)->cgroup;
+ pid_t pid;
int ret;

+ if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
+ return -EINVAL;
+
if (!cgroup_lock_live_group(cgrp))
return -ENODEV;

@@ -2305,7 +2311,7 @@ retry_find_task:
put_task_struct(tsk);
out_unlock_cgroup:
mutex_unlock(&cgroup_mutex);
- return ret;
+ return ret ?: nbytes;
}

/**
@@ -2339,16 +2345,16 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
}
EXPORT_SYMBOL_GPL(cgroup_attach_task_all);

-static int cgroup_tasks_write(struct cgroup_subsys_state *css,
- struct cftype *cft, u64 pid)
+static ssize_t cgroup_tasks_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
{
- return attach_task_by_pid(css->cgroup, pid, false);
+ return __cgroup_procs_write(of, buf, nbytes, off, false);
}

-static int cgroup_procs_write(struct cgroup_subsys_state *css,
- struct cftype *cft, u64 tgid)
+static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
{
- return attach_task_by_pid(css->cgroup, tgid, true);
+ return __cgroup_procs_write(of, buf, nbytes, off, true);
}

static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
@@ -3951,7 +3957,7 @@ static struct cftype cgroup_base_files[] = {
.seq_stop = cgroup_pidlist_stop,
.seq_show = cgroup_pidlist_show,
.private = CGROUP_FILE_PROCS,
- .write_u64 = cgroup_procs_write,
+ .write = cgroup_procs_write,
.mode = S_IRUGO | S_IWUSR,
},
{
@@ -4000,7 +4006,7 @@ static struct cftype cgroup_base_files[] = {
.seq_stop = cgroup_pidlist_stop,
.seq_show = cgroup_pidlist_show,
.private = CGROUP_FILE_TASKS,
- .write_u64 = cgroup_tasks_write,
+ .write = cgroup_tasks_write,
.mode = S_IRUGO | S_IWUSR,
},
{
--
1.9.0