Commit 896f5199 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: unify read path so that seq_file is always used 



With the recent removal of cftype->read() and ->read_map(), only three
operations are remaining, ->read_u64(), ->read_s64() and
->read_seq_string().  Currently, the first two are handled directly
while the last is handled through seq_file.

It is trivial to serve the first two through the seq_file path too.
This patch restructures read path so that all operations are served
through cgroup_seqfile_show().  This makes all cgroup files seq_file -
single_open/release() are now used by default,
cgroup_seqfile_operations is dropped, and cgroup_file_operations uses
seq_read() for read.

This simplifies the code and makes the read path easy to convert to
use kernfs.

Note that, while cgroup_file_operations uses seq_read() for read, it
still uses generic_file_llseek() for seeking instead of seq_lseek().
This is different from cgroup_seqfile_operations but shouldn't break
anything and brings the seeking behavior aligned with kernfs.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent a742c59d

kernel/cgroup.c

+15 −53
Original line number Diff line number Diff line
@@ -2295,42 +2295,6 @@ out_free: 
	return ret ?: nbytes;

}



static ssize_t cgroup_read_u64(struct cgroup_subsys_state *css,

			       struct cftype *cft, struct file *file,

			       char __user *buf, size_t nbytes, loff_t *ppos)

{

	char tmp[CGROUP_LOCAL_BUFFER_SIZE];

	u64 val = cft->read_u64(css, cft);

	int len = sprintf(tmp, "%llu\n", (unsigned long long) val);



	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);

}



static ssize_t cgroup_read_s64(struct cgroup_subsys_state *css,

			       struct cftype *cft, struct file *file,

			       char __user *buf, size_t nbytes, loff_t *ppos)

{

	char tmp[CGROUP_LOCAL_BUFFER_SIZE];

	s64 val = cft->read_s64(css, cft);

	int len = sprintf(tmp, "%lld\n", (long long) val);



	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);

}



static ssize_t cgroup_file_read(struct file *file, char __user *buf,

				size_t nbytes, loff_t *ppos)

{

	struct cfent *cfe = __d_cfe(file->f_dentry);

	struct cftype *cft = __d_cft(file->f_dentry);

	struct cgroup_subsys_state *css = cfe->css;



	if (cft->read_u64)

		return cgroup_read_u64(css, cft, file, buf, nbytes, ppos);

	if (cft->read_s64)

		return cgroup_read_s64(css, cft, file, buf, nbytes, ppos);

	return -EINVAL;

}



/*

 * seqfile ops/methods for returning structured data. Currently just

 * supports string->u64 maps, but can be extended in future.
@@ -2342,15 +2306,17 @@ static int cgroup_seqfile_show(struct seq_file *m, void *arg) 
	struct cftype *cft = cfe->type;

	struct cgroup_subsys_state *css = cfe->css;



	if (cft->read_seq_string)

		return cft->read_seq_string(css, cft, m);

}



static const struct file_operations cgroup_seqfile_operations = {

	.read = seq_read,

	.write = cgroup_file_write,

	.llseek = seq_lseek,

	.release = cgroup_file_release,

};

	if (cft->read_u64)

		seq_printf(m, "%llu\n", cft->read_u64(css, cft));

	else if (cft->read_s64)

		seq_printf(m, "%lld\n", cft->read_s64(css, cft));

	else

		return -EINVAL;

	return 0;

}



static int cgroup_file_open(struct inode *inode, struct file *file)

{
@@ -2387,12 +2353,10 @@ static int cgroup_file_open(struct inode *inode, struct file *file) 
	WARN_ON_ONCE(cfe->css && cfe->css != css);

	cfe->css = css;



	if (cft->read_seq_string) {

		file->f_op = &cgroup_seqfile_operations;

		err = single_open(file, cgroup_seqfile_show, cfe);

	} else if (cft->open) {

	if (cft->open)

		err = cft->open(inode, file);

	}

	else

		err = single_open(file, cgroup_seqfile_show, cfe);



	if (css->ss && err)

		css_put(css);
@@ -2406,9 +2370,7 @@ static int cgroup_file_release(struct inode *inode, struct file *file) 


	if (css->ss)

		css_put(css);

	if (file->f_op == &cgroup_seqfile_operations)

		single_release(inode, file);

	return 0;

	return single_release(inode, file);

}



/*
@@ -2519,7 +2481,7 @@ static ssize_t cgroup_listxattr(struct dentry *dentry, char *buf, size_t size) 
}



static const struct file_operations cgroup_file_operations = {

	.read = cgroup_file_read,

	.read = seq_read,

	.write = cgroup_file_write,

	.llseek = generic_file_llseek,

	.open = cgroup_file_open,

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