linux-ext4 - Re: [PATCH v4 3/8] ext4: introduce new callback for IOMAP

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Message-ID: <20191009120816.GH14749@poseidon.bobrowski.net>
Date:   Wed, 9 Oct 2019 23:08:18 +1100
From:   Matthew Bobrowski <mbobrowski@...browski.org>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v4 3/8] ext4: introduce new callback for IOMAP_REPORT
 operations

On Wed, Oct 09, 2019 at 11:30:21AM +0530, Ritesh Harjani wrote:
> > +static u16 ext4_iomap_check_delalloc(struct inode *inode,
> > +				     struct ext4_map_blocks *map)
> > +{
> > +	struct extent_status es;
> > +	ext4_lblk_t end = map->m_lblk + map->m_len - 1;
> > +
> > +	ext4_es_find_extent_range(inode, &ext4_es_is_delayed, map->m_lblk,
> > +				  end, &es);
> > +
> > +	/* Entire range is a hole */
> > +	if (!es.es_len || es.es_lblk > end)
> > +		return IOMAP_HOLE;
> > +	if (es.es_lblk <= map->m_lblk) {
> > +		ext4_lblk_t offset = 0;
> > +
> > +		if (es.es_lblk < map->m_lblk)
> > +			offset = map->m_lblk - es.es_lblk;
> > +		map->m_lblk = es.es_lblk + offset;
> This looks redundant no? map->m_lblk never changes actually.
> So this is not needed here.

Well, it depends if map->m_lblk == es.es_lblk + offset prior to the
assignment? If that's always true, then sure, it'd be redundant. But
honestly, I don't know what the downstream effect would be if this was
removed. I'd have to look at the code, perform some tests, and figure
it out.

> > +	map.m_lblk = first_block;
> > +	map.m_len = last_block = first_block + 1;
> > +	ret = ext4_map_blocks(NULL, inode, &map, 0);
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret == 0)
> > +		type = ext4_iomap_check_delalloc(inode, &map);
> > +	return ext4_set_iomap(inode, iomap, type, first_block, &map);
> We don't need to send first_block here. Since map->m_lblk
> is same as first_block.
> Also with Jan comment, we don't even need 'type' parameter.
> Then we should be able to rename the function
> ext4_set_iomap ==> ext4_map_to_iomap. This better reflects what it is
> doing. Thoughts?

Depends on what we conclude in 1/8. :)

I'm for removing 'first_block', but still not convinced removing
'type' is heading down the right track if I were to forward think a
little.

--<M>--