linux-kernel - [PATCH 02/12] cgroup: add hook seq_show_cft with also the owning cftype as parameter

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Date:   Mon, 12 Nov 2018 10:56:22 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Angelo Ruocco <angeloruocco90@...il.com>,
        Dennis Zhou <dennis@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        Liu Bo <bo.liu@...ux.alibaba.com>,
        Bart Van Assche <bvanassche@....org>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, linus.walleij@...aro.org,
        broonie@...nel.org, bfq-iosched@...glegroups.com,
        oleksandr@...alenko.name, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Paolo Valente <paolo.valente@...aro.org>
Subject: [PATCH 02/12] cgroup: add hook seq_show_cft with also the owning cftype as parameter

The current implementation of the seq_show hook in the cftype struct
has only, as parameters, the seq_file to write to and the arguments
passed by the command line. Thus, the only way to retrieve the cftype
that owns an instance of such hook function is by using the accessor
in the seq_file itself.

But in a future scenario where the same file may be shared by multiple
cftypes, this accessor will point only to the first of the cftypes
linked to the seq_file. It will then be impossible to access the
cftype owning the seq_show function within the seq_show itself, unless
such cftype is the first one.

This commit adds an additional seq_show_cft hook that has as a formal
parameter also the cftype that owns the function.

Signed-off-by: Angelo Ruocco <angeloruocco90@...il.com>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 include/linux/cgroup-defs.h |  3 ++-
 kernel/cgroup/cgroup.c      | 15 +++++++++------
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 5e1694fe035b..7841db6e7fb3 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -543,8 +543,9 @@ struct cftype {
 	 */
 	s64 (*read_s64)(struct cgroup_subsys_state *css, struct cftype *cft);
 
-	/* generic seq_file read interface */
+	/* generic seq_file read interfaces*/
 	int (*seq_show)(struct seq_file *sf, void *v);
+	int (*seq_show_cft)(struct seq_file *sf, struct cftype *cft, void *v);
 
 	/* optional ops, implement all or none */
 	void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 8b79318810ad..74012b61fe19 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1448,7 +1448,8 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
 {
 	umode_t mode = 0;
 
-	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
+	if (cft->read_u64 || cft->read_s64 || cft->seq_show ||
+	    cft->seq_show_cft)
 		mode |= S_IRUGO;
 
 	if (cft->write_u64 || cft->write_s64 || cft->write) {
@@ -3549,17 +3550,19 @@ static int cgroup_seqfile_show(struct seq_file *m, void *arg)
 {
 	struct cftype *cft = seq_cft(m);
 	struct cgroup_subsys_state *css = seq_css(m);
+	int ret = 0;
 
 	if (cft->seq_show)
-		return cft->seq_show(m, arg);
-
-	if (cft->read_u64)
+		ret = cft->seq_show(m, arg);
+	else if (cft->seq_show_cft)
+		ret = cft->seq_show_cft(m, cft, arg);
+	else 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;
+		ret = -EINVAL;
+	return ret;
 }
 
 static struct kernfs_ops cgroup_kf_single_ops = {
-- 
2.16.1