linux-ext4 - Re: [PATCH] ext4: add sysfs attr /sys/fs/ext4/<disk>/journal

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Date:   Thu, 21 Feb 2019 11:52:58 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
CC:     <linux-fsdevel@...r.kernel.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ext4: add sysfs attr /sys/fs/ext4/<disk>/journal_task

On Mon, Feb 04, 2019 at 01:17:43PM +0300, Konstantin Khlebnikov wrote:
> 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 <khlebnikov@...dex-team.ru>

Thanks, applied with one change; if the file system does not have a
journal, reading the /sys/fs/ext4/<disk>/journal_task will return
"<none>" instead of returning a ESRCH error.

	 	    	      	      - Ted