cgroup: unify pidlist and other file handling

In preparation of conversion to kernfs, cgroup file handling is
updated so that it can be easily mapped to kernfs.  With the previous
changes, the difference between pidlist and other files are very
small.  Both are served by seq_file in a pretty standard way with the
only difference being !pidlist files use single_open().

This patch adds cftype->seq_start(), ->seq_next and ->seq_stop() and
implements the matching cgroup_seqfile_start/next/stop() which either
emulates single_open() behavior or invokes cftype->seq_*() operations
if specified.  This allows using single seq_operations for both
pidlist and other files and makes cgroup_pidlist_operations and
cgorup_pidlist_open() no longer necessary.  As cgroup_pidlist_open()
was the only user of cftype->open(), the method is dropped together.

This brings cftype file interface very close to kernfs interface and
mapping shouldn't be too difficult.  Once converted to kernfs, most of
the plumbing code including cgroup_seqfile_*() will be removed as
kernfs provides those facilities.

This patch does not introduce any behavior changes.

v2: Refreshed on top of the updated "cgroup: introduce struct
    cgroup_pidlist_open_file".

v3: Refreshed on top of the updated "cgroup: attach cgroup_open_file
    to all cgroup files".

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b32a0f8ae9ad..8b9a594f0c92 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -434,7 +434,6 @@ struct cftype {
 	 */
 	struct cgroup_subsys *ss;
 
-	int (*open)(struct inode *inode, struct file *file);
 	/*
 	 * read_u64() is a shortcut for the common case of returning a
 	 * single integer. Use it in place of read()
@@ -448,6 +447,11 @@ struct cftype {
 	/* generic seq_file read interface */
 	int (*seq_show)(struct seq_file *sf, void *v);
 
+	/* optional ops, implement all or none */
+	void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
+	void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
+	void (*seq_stop)(struct seq_file *sf, void *v);
+
 	/*
 	 * write_u64() is a shortcut for the common case of accepting
 	 * a single integer (as parsed by simple_strtoull) from