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Date: Tue, 15 Mar 2016 00:33:04 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Bob Peterson <rpeterso@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, Jan Kara <jack@suse.cz>,
	Al Viro <viro@ZenIV.linux.org.uk>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [vfs PATCH v3 2/4] VFS: Add new __generic_iomap_fiemap interface
Message-ID: <20160315073304.GF11669@infradead.org>
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> +	while ((ret == 0) && (start < isize) && len) {

no need for both sets of inner braces.

> +		memset(&iom, 0, sizeof(iom));
> +		ret = iomap(inode->i_mapping, start, len, &iom);
> +		if (ret)
> +			break;
> +
> +		if (!iomap_needs_allocation(&iom)) {

I don't think the iomap_needs_allocation, because the decision if
something needs an allocation is up to the beholder.  E.g. in this case
you want to report block numbers of holes and unwritten extents.

> +			if (prev_iom.blkno)
> +				ret = fiemap_fill_next_extent(fieinfo,
> +							      prev_iom.offset,
> +							      blk_to_logical(inode,

the iomap interface as used for pnfs and the multi page writes that I
pointed you to in the last reply use file system blocks as unit, so the
blk_to_logical should go away.