linux-kernel - Re: [PATCH v7] iomap: make inline data support more flexible

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Message-ID: <CAHpGcMJhuSApy4eg9jKe2pYq4d7bY-Lg-Bmo9tOANghQ2Hxo-A@mail.gmail.com>
Date:   Mon, 26 Jul 2021 14:27:12 +0200
From:   Andreas Grünbacher <andreas.gruenbacher@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>,
        Gao Xiang <hsiangkao@...ux.alibaba.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Huang Jianan <huangjianan@...o.com>,
        linux-erofs@...ts.ozlabs.org,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7] iomap: make inline data support more flexible

Am Mo., 26. Juli 2021 um 14:17 Uhr schrieb Christoph Hellwig <hch@....de>:
>
> > Subject: iomap: Support tail packing
>
> I can't say I like this "tail packing" language here when we have the
> perfectly fine inline wording.  Same for various comments in the actual
> code.
>
> > +     /* inline and tail-packed data must start page aligned in the file */
> > +     if (WARN_ON_ONCE(offset_in_page(iomap->offset)))
> > +             return -EIO;
> > +     if (WARN_ON_ONCE(size > PAGE_SIZE - offset_in_page(iomap->inline_data)))
> > +             return -EIO;
>
> Why can't we use iomap_inline_data_size_valid here?

We can now. Gao, can you change that?

> That is how can size be different from iomap->length?

Quoting from my previous reply,

"In the iomap_readpage case (iomap_begin with flags == 0),
iomap->length will be the amount of data up to the end of the inode.
In the iomap_file_buffered_write case (iomap_begin with flags ==
IOMAP_WRITE), iomap->length will be the size of iomap->inline_data.
(For extending writes, we need to write beyond the current end of
inode.) So iomap->length isn't all that useful for
iomap_read_inline_data."

> Shouldn't the offset_in_page also go into iomap_inline_data_size_valid,
> which should probably be called iomap_inline_data_valid then?

Hmm, not sure what you mean: iomap_inline_data_size_valid does take
offset_in_page(iomap->inline_data) into account.

> >       if (iomap->type == IOMAP_INLINE) {
> > +             int ret = iomap_read_inline_data(inode, page, iomap);
> > +             return ret ?: PAGE_SIZE;
>
> The ?: expression without the first leg is really confuing.  Especially
> if a good old if is much more readable here.

I'm sure Gao can change this.

>                 int ret = iomap_read_inline_data(inode, page, iomap);
>
>                 if (ret)
>                         return ret;
>                 return PAGE_SIZE;
>
> > +             copied = copy_from_iter(iomap_inline_data(iomap, pos), length, iter);
>
>
> > +             copied = copy_to_iter(iomap_inline_data(iomap, pos), length, iter);
>
> Pleae avoid the overly long lines.

I thought people were okay with 80 character long lines?

Thanks,
Andreas