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Commit b4168640 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: implement cftype->write() 



During the recent conversion to kernfs, cftype's seq_file operations
are updated so that they are directly mapped to kernfs operations and
thus can fully access the associated kernfs and cgroup contexts;
however, write path hasn't seen similar updates and none of the
existing write operations has access to, for example, the associated
kernfs_open_file.

Let's introduce a new operation cftype->write() which maps directly to
the kernfs write operation and has access to all the arguments and
contexts.  This will replace ->write_string() and ->trigger() and ease
manipulation of kernfs active protection from cgroup file operations.

Two accessors - of_cft() and of_css() - are introduced to enable
accessing the associated cgroup context from cftype->write() which
only takes kernfs_open_file for the context information.  The
accessors for seq_file operations - seq_cft() and seq_css() - are
rewritten to wrap the of_ accessors.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent ec903c0c

include/linux/cgroup.h

+23 −4
Original line number Diff line number Diff line
@@ -515,6 +515,15 @@ struct cftype { 
	 */

	int (*trigger)(struct cgroup_subsys_state *css, unsigned int event);



	/*

	 * write() is the generic write callback which maps directly to

	 * kernfs write operation and overrides all other operations.

	 * Maximum write size is determined by ->max_write_len.  Use

	 * of_css/cft() to access the associated css and cft.

	 */

	ssize_t (*write)(struct kernfs_open_file *of,

			 char *buf, size_t nbytes, loff_t off);



#ifdef CONFIG_DEBUG_LOCK_ALLOC

	struct lock_class_key	lockdep_key;

#endif
@@ -552,14 +561,24 @@ static inline ino_t cgroup_ino(struct cgroup *cgrp) 
		return 0;

}



static inline struct cftype *seq_cft(struct seq_file *seq)

/* cft/css accessors for cftype->write() operation */

static inline struct cftype *of_cft(struct kernfs_open_file *of)

{

	struct kernfs_open_file *of = seq->private;



	return of->kn->priv;

}



struct cgroup_subsys_state *seq_css(struct seq_file *seq);

struct cgroup_subsys_state *of_css(struct kernfs_open_file *of);



/* cft/css accessors for cftype->seq_*() operations */

static inline struct cftype *seq_cft(struct seq_file *seq)

{

	return of_cft(seq->private);

}



static inline struct cgroup_subsys_state *seq_css(struct seq_file *seq)

{

	return of_css(seq->private);

}



/*

 * Name / path handling functions.  All are thin wrappers around the kernfs

kernel/cgroup.c

+8 −6
Original line number Diff line number Diff line
@@ -283,11 +283,10 @@ static inline bool cgroup_is_dead(const struct cgroup *cgrp) 
	return test_bit(CGRP_DEAD, &cgrp->flags);

}



struct cgroup_subsys_state *seq_css(struct seq_file *seq)

struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)

{

	struct kernfs_open_file *of = seq->private;

	struct cgroup *cgrp = of->kn->parent->priv;

	struct cftype *cft = seq_cft(seq);

	struct cftype *cft = of_cft(of);



	/*

	 * This is open and unprotected implementation of cgroup_css().
@@ -302,7 +301,7 @@ struct cgroup_subsys_state *seq_css(struct seq_file *seq) 
	else

		return &cgrp->dummy_css;

}

EXPORT_SYMBOL_GPL(seq_css);

EXPORT_SYMBOL_GPL(of_css);



/**

 * cgroup_is_descendant - test ancestry
@@ -1035,8 +1034,8 @@ static umode_t cgroup_file_mode(const struct cftype *cft) 
	if (cft->read_u64 || cft->read_s64 || cft->seq_show)

		mode |= S_IRUGO;



	if (cft->write_u64 || cft->write_s64 || cft->write_string ||

	    cft->trigger)

	if (cft->write_u64 || cft->write_s64 || cft->write ||

	    cft->write_string || cft->trigger)

		mode |= S_IWUSR;



	return mode;
@@ -2726,6 +2725,9 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf, 
	struct cgroup_subsys_state *css;

	int ret;



	if (cft->write)

		return cft->write(of, buf, nbytes, off);



	/*

	 * kernfs guarantees that a file isn't deleted with operations in

	 * flight, which means that the matching css is and stays alive and