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Date: Mon, 2 Sep 2019 08:23:23 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Gao Xiang <gaoxiang25@huawei.com>
Subject: Re: [PATCH 00/21] erofs: patchset addressing Christoph's comments
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Cc: devel@driverdev.osuosl.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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On Mon, Sep 02, 2019 at 10:24:52PM +0800, Gao Xiang wrote:
> > code quality stuff.  We're not addressing the issues with large amounts
> > of functionality duplicating VFS helpers.
> 
> You means killing erofs_get_meta_page or avoid erofs_read_raw_page?
> 
>  - For killing erofs_get_meta_page, here is the current erofs_get_meta_page:

> I think it is simple enough. read_cache_page need write a similar
> filler, or read_cache_page_gfp will call .readpage, and then
> introduce buffer_heads, that is what I'd like to avoid now (no need these
> bd_inode buffer_heads in memory...)

If using read_cache_page_gfp and ->readpage works, please do.  The
fact that the block device inode uses buffer heads is an implementation
detail that might not last very long and should be invisible to you.
It also means you can get rid of a lot of code that you don't have
to maintain and others don't have to update for global API changes.

>  - For erofs_read_raw_page, it can be avoided after iomap tail-end packing
>    feature is done... If we remove it now, it will make EROFS broken.
>    It is no urgent and Chao will focus on iomap tail-end packing feature.

Ok.  I wish we would have just sorted this out beforehand, which we
could have trivially done without all that staging mess.