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: Konstantin Khlebnikov <[email protected]> --- Documentation/ABI/testing/sysfs-fs-ext4 | 7 +++++++ fs/ext4/sysfs.c | 13 +++++++++++++ 2 files changed, 20 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-fs-ext4 b/Documentation/ABI/testing/sysfs-fs-ext4 index c631253cf85c..78604db56279 100644 --- a/Documentation/ABI/testing/sysfs-fs-ext4 +++ b/Documentation/ABI/testing/sysfs-fs-ext4 @@ -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" <[email protected]> +Description: + This file is read-only and shows the pid of journal thread in + current pid-namespace or 0 if task is unreachable. diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c index 9212a026a1f1..60085b2e41ed 100644 --- a/fs/ext4/sysfs.c +++ b/fs/ext4/sysfs.c @@ -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 -ESRCH; + 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;
