linux-ext4 - Re: [PATCH] iomap: Add inline data support to iomap_readpage

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Message-ID: <CAHc6FU6vpbobB6fOFY5z8KvLdJC_5_zRGJMXBX9EZFkN1Z3=DQ@mail.gmail.com>
Date:   Mon, 2 Jul 2018 17:05:18 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     cluster-devel <cluster-devel@...hat.com>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] iomap: Add inline data support to iomap_readpage_actor

On 2 July 2018 at 14:52, Christoph Hellwig <hch@....de> wrote:
> On Sun, Jul 01, 2018 at 11:43:43PM +0200, Andreas Gruenbacher wrote:
>> > +               WARN_ON_ONCE(plen != PAGE_SIZE);
>>
>> Inline mappings only extend to the end of the file (iomap->offset == 0
>> && iomap->length == inode->i_size), so length and plen will be
>> inode->i_size here. This assertion should just be removed.
>
> But we should generally still return PAGE_SIZE from iomap_begin
> because we cover the whole page and zero the rest, don't we?

iomap_begin doesn't know when it's being called for readpage. Direct
I/O reads don't pad to the page size,  for example, so handling the
padding in the caller seems reasonable. If you compare with regular
block-based mappings, those are also block but not necessarily page
aligned.

For stuffed files, iomap_begin will return an IOMAP_HOLE mapping for
offsets beyond the end of the file, so iterating beyond the end of the
file is fine (even if readpage doesn't do that).

> Either way, I can remove the assert from now.

Yes, thanks.

Andreas