linux-ext4 - Re: [PATCH v8 30/32] ext4: Send notifications on error

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Date:   Tue, 19 Oct 2021 18:01:52 +0200
From:   Jan Kara <jack@...e.cz>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     jack@...e.com, amir73il@...il.com, djwong@...nel.org,
        tytso@....edu, david@...morbit.com, dhowells@...hat.com,
        khazhy@...gle.com, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-api@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH v8 30/32] ext4: Send notifications on error

On Tue 19-10-21 17:44:26, Jan Kara wrote:
> On Mon 18-10-21 21:00:13, Gabriel Krisman Bertazi wrote:
> > Send a FS_ERROR message via fsnotify to a userspace monitoring tool
> > whenever a ext4 error condition is triggered.  This follows the existing
> > error conditions in ext4, so it is hooked to the ext4_error* functions.
> > 
> > It also follows the current dmesg reporting in the format.  The
> > filesystem message is composed mostly by the string that would be
> > otherwise printed in dmesg.
> > 
> > A new ext4 specific record format is exposed in the uapi, such that a
> > monitoring tool knows what to expect when listening errors of an ext4
> > filesystem.
> > 
> > Reviewed-by: Amir Goldstein <amir73il@...il.com>
> > Reviewed-by: Theodore Ts'o <tytso@....edu>
> > Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
> 
> Looks good to me. Feel free to add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>

Hum, I actually retract this because the code doesn't match what is written
in the documentation and I'm not 100% sure what is correct. In particular:

> > @@ -759,6 +760,8 @@ void __ext4_error(struct super_block *sb, const char *function,
> >  		       sb->s_id, function, line, current->comm, &vaf);
> >  		va_end(args);
> >  	}
> > +	fsnotify_sb_error(sb, NULL, error);
> > +

E.g. here you pass the 'error' to fsnotify. This will be just standard
'errno' number, not ext4 error code as described in the documentation. Also
note that frequently 'error' will be 0 which gets magically transformed to
EFSCORRUPTED in save_error_info() in the ext4 error handling below. So
there's clearly some more work to do...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR