linux-kernel - Re: [rfc][patch] mm, fs: warn on missing address space operations

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Message-ID: <84144f021003220100r29ee1ff2x11a66531e0104167@mail.gmail.com>
Date:	Mon, 22 Mar 2010 10:00:54 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Nick Piggin <npiggin@...e.de>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [rfc][patch] mm, fs: warn on missing address space operations

On Mon, Mar 22, 2010 at 6:56 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 22 Mar 2010 16:39:37 +1100 Nick Piggin <npiggin@...e.de> wrote:
>
>> It's ugly and lazy that we do these default aops in case it has not
>> been filled in by the filesystem.
>>
>> A NULL operation should always mean either: we don't support the
>> operation; we don't require any action; or a bug in the filesystem,
>> depending on the context.
>>
>> In practice, if we get rid of these fallbacks, it will be clearer
>> what operations are used by a given address_space_operations struct,
>> reduce branches, reduce #if BLOCK ifdefs, and should allow us to get
>> rid of all the buffer_head knowledge from core mm and fs code.
>
> I guess this is one way of waking people up.
>
> What happens is that hundreds of bug reports land in my inbox and I get
> to route them to various maintainers, most of whom don't exist, so
> warnings keep on landing in my inbox.  Please send a mailing address for
> my invoices.
>
> It would be more practical, more successful and quicker to hunt down
> the miscreants and send them rude emails.  Plus it would save you
> money.
>
>> We could add a patch like this which spits out a recipe for how to fix
>> up filesystems and get them all converted quite easily.
>>
>> ...
>>
>> @@ -40,8 +40,14 @@ void do_invalidatepage(struct page *page
>>       void (*invalidatepage)(struct page *, unsigned long);
>>       invalidatepage = page->mapping->a_ops->invalidatepage;
>>  #ifdef CONFIG_BLOCK
>> -     if (!invalidatepage)
>> +     if (!invalidatepage) {
>> +             static bool warned = false;
>> +             if (!warned) {
>> +                     warned = true;
>> +                     print_symbol("address_space_operations %s missing invalidatepage method. Use block_invalidatepage.\n", (unsigned long)page->mapping->a_ops);
>> +             }
>>               invalidatepage = block_invalidatepage;
>> +     }
>
> erk, I realise 80 cols can be a pain, but 165 cols is just out of
> bounds.  Why not
>
>        /* this fs should use block_invalidatepage() */
>        WARN_ON_ONCE(!invalidatepage);

/me gets his paint bucket...

How about

    WARN_ONCE(!invalidatepage, "this fs should use block_invalidatepage()")

                           Pekka
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