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Commit bc1d69d6 authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Theodore Ts'o
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ext4: add sysfs attr /sys/fs/ext4/<disk>/journal_task 



This is useful for moving journal thread into cgroup or
for tracing it with ftrace/perf/blktrace.

For now the only way is `pgrep jbd2/$DISK` but this is not reliable:
name may be longer than "comm" limit and any task could mock it.

Attribute shows pid in current pid-namespace or 0 if task is unreachable.

Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 231fe82b

Documentation/ABI/testing/sysfs-fs-ext4

+7 −0
Original line number Diff line number Diff line
@@ -109,3 +109,10 @@ Description: 
		write operation (since a 4k random write might turn

		into a much larger write due to the zeroout

		operation).



What:		/sys/fs/ext4/<disk>/journal_task

Date:		February 2019

Contact:	"Theodore Ts'o" <tytso@mit.edu>

Description:

		This file is read-only and shows the pid of journal thread in

		current pid-namespace or 0 if task is unreachable.

fs/ext4/sysfs.c

+13 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ typedef enum { 
	attr_feature,

	attr_pointer_ui,

	attr_pointer_atomic,

	attr_journal_task,

} attr_id_t;



typedef enum {
@@ -125,6 +126,14 @@ static ssize_t trigger_test_error(struct ext4_sb_info *sbi, 
	return count;

}



static ssize_t journal_task_show(struct ext4_sb_info *sbi, char *buf)

{

	if (!sbi->s_journal)

		return snprintf(buf, PAGE_SIZE, "<none>\n");

	return snprintf(buf, PAGE_SIZE, "%d\n",

			task_pid_vnr(sbi->s_journal->j_task));

}



#define EXT4_ATTR(_name,_mode,_id)					\

static struct ext4_attr ext4_attr_##_name = {				\

	.attr = {.name = __stringify(_name), .mode = _mode },		\
@@ -188,6 +197,7 @@ EXT4_RW_ATTR_SBI_UI(msg_ratelimit_burst, s_msg_ratelimit_state.burst); 
EXT4_RO_ATTR_ES_UI(errors_count, s_error_count);

EXT4_ATTR(first_error_time, 0444, first_error_time);

EXT4_ATTR(last_error_time, 0444, last_error_time);

EXT4_ATTR(journal_task, 0444, journal_task);



static unsigned int old_bump_val = 128;

EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val);
@@ -217,6 +227,7 @@ static struct attribute *ext4_attrs[] = { 
	ATTR_LIST(errors_count),

	ATTR_LIST(first_error_time),

	ATTR_LIST(last_error_time),

	ATTR_LIST(journal_task),

	NULL,

};
@@ -304,6 +315,8 @@ static ssize_t ext4_attr_show(struct kobject *kobj, 
		return print_tstamp(buf, sbi->s_es, s_first_error_time);

	case attr_last_error_time:

		return print_tstamp(buf, sbi->s_es, s_last_error_time);

	case attr_journal_task:

		return journal_task_show(sbi, buf);

	}



	return 0;