linux-ext4 - Re: [RFC PATCH] ext4: add unmount filesystem message

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Date:   Tue, 12 Apr 2022 12:01:37 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <jack@...e.cz>, <yukuai3@...wei.com>,
        <yebin10@...wei.com>, <liuzhiqiang26@...wei.com>,
        <liangyun2@...wei.com>
Subject: Re: [RFC PATCH] ext4: add unmount filesystem message

Zhang Yi <yi.zhang@...wei.com> writes:

> Now that we have kernel message at mount time, system administrator
> could acquire the mount time, device and options easily. But we don't
> have corresponding unmounting message at umount time, so we cannot know
> if someone umount a filesystem easily. Some of the modern filesystems
> (e.g. xfs) have the umounting kernel message, so add one for ext4
> filesystem for convenience.
>
>  EXT4-fs (sdb): mounted filesystem with ordered data mode. Quota mode: none.
>  EXT4-fs (sdb): unmounting filesystem.

I don't think sysadmins should be relying on the kernel log for this,
since the information can easily be overwritten by new messages there.
Is there a reason why you can't just monitor /proc/self/mountinfo?

> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> ---
>  fs/ext4/super.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 81749eaddf4c..bdecf62f4b55 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1199,6 +1199,9 @@ static void ext4_put_super(struct super_block *sb)
>  	int aborted = 0;
>  	int i, err;
>  
> +	if (___ratelimit(&ext4_mount_msg_ratelimit, "EXT4-fs unmount"))
> +		ext4_msg(sb, KERN_INFO, "unmounting filesystem.");
> +
>  	ext4_unregister_li_request(sb);
>  	ext4_quota_off_umount(sb);

-- 
Gabriel Krisman Bertazi