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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <20201208003117.342047-6-krisman@collabora.com>
References: <20201208003117.342047-6-krisman@collabora.com> <20201208003117.342047-1-krisman@collabora.com>
To:     Gabriel Krisman Bertazi <krisman@collabora.com>
Cc:     dhowells@redhat.com, viro@zeniv.linux.org.uk, tytso@mit.edu,
        khazhy@google.com, adilger.kernel@dilger.ca,
        linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        kernel@collabora.com
Subject: Re: [PATCH 5/8] vfs: Include origin of the SB error notification
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Content-ID: <952749.1607431868.1@warthog.procyon.org.uk>
Date:   Tue, 08 Dec 2020 12:51:08 +0000
Message-ID: <952750.1607431868@warthog.procyon.org.uk>
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Gabriel Krisman Bertazi <krisman@collabora.com> wrote:

> @@ -130,6 +131,8 @@ struct superblock_error_notification {
>  	__u32	error_cookie;
>  	__u64	inode;
>  	__u64	block;
> +	char	function[SB_NOTIFICATION_FNAME_LEN];
> +	__u16	line;
>  	char	desc[0];
>  };

As Darrick said, this is a UAPI breaker, so you shouldn't do this (you can,
however, merge this ahead a patch).  Also, I would put the __u16 before the
char[].

That said, I'm not sure whether it's useful to include the function name and
line.  Both fields are liable to change over kernel commits, so it's not
something userspace can actually interpret.  I think you're better off dumping
those into dmesg.

Further, this reduces the capacity of desc[] significantly - I don't know if
that's a problem.

And yet further, there's no room for addition of new fields with the desc[]
buffer on the end.  Now maybe you're planning on making use of desc[] for
text-encoding?

David