linux-kernel - RE: [PATCH v2 2/9] ext2: tell DAX the size of allocation holes

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Message-ID: <DM2PR21MB0089423BC46778AC1A511995CBFD0@DM2PR21MB0089.namprd21.prod.outlook.com>
Date:   Sat, 10 Sep 2016 15:55:17 +0000
From:   Matthew Wilcox <mawilcox@...rosoft.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Theodore Ts'o <tytso@....edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
        Dave Chinner <david@...morbit.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Andreas Dilger" <adilger.kernel@...ger.ca>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: RE: [PATCH v2 2/9] ext2: tell DAX the size of allocation holes

From: Christoph Hellwig [mailto:hch@...radead.org]
> Either way we need to get rid of buffer_heads, and another aop that is entirely
> caller specific is unaceptable.

I finally figured out what you actually meant by this.  You mean that instead of having an aop->populate_pfn, you want to define a populate_pfn_t callback and pass it in.

Something like this:

int ext2_populate_pfn(struct address_space *mapping, pgoff_t pgoff)
{
	struct iomap iomap;
	...
	return dax_populate_pfn(mapping, pgoff, &iomap);
}

int ext2_dax_fault(vma, vmf)
{
	...
	ret = dax_fault(vma, vmf, ext2_populate_pfn);
	...
}

I don't have a problem with that.  I'll work up something along those lines next week.