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From: Jan Kara <jack@suse.cz>
To: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Cc: Jan Kara <jack@suse.cz>,
	tytso@mit.edu, adilger.kernel@dilger.ca,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	hch@infradead.org, david@fromorbit.com, darrick.wong@oracle.com
Subject: Re: [PATCH v4 1/8] ext4: move out iomap field population into separate helper
Date: Wed, 9 Oct 2019 15:06:09 +0200
Message-ID: <20191009130609.GD5050@quack2.suse.cz> (raw)
In-Reply-To: <20191009085721.GA1534@poseidon.bobrowski.net>

On Wed 09-10-19 19:57:23, Matthew Bobrowski wrote:
> On Tue, Oct 08, 2019 at 12:27:09PM +0200, Jan Kara wrote:
> > On Thu 03-10-19 21:33:09, Matthew Bobrowski wrote:
> > > +static int ext4_set_iomap(struct inode *inode, struct iomap *iomap, u16 type,
> > > +			  unsigned long first_block, struct ext4_map_blocks *map)
> > > +{
> > > +	u8 blkbits = inode->i_blkbits;
> > > +
> > > +	iomap->flags = 0;
> > > +	if (ext4_inode_datasync_dirty(inode))
> > > +		iomap->flags |= IOMAP_F_DIRTY;
> > > +	iomap->bdev = inode->i_sb->s_bdev;
> > > +	iomap->dax_dev = EXT4_SB(inode->i_sb)->s_daxdev;
> > > +	iomap->offset = (u64) first_block << blkbits;
> > > +	iomap->length = (u64) map->m_len << blkbits;
> > > +
> > > +	if (type) {
> > > +		iomap->type = type;
> > > +		iomap->addr = IOMAP_NULL_ADDR;
> > > +	} else {
> > > +		if (map->m_flags & EXT4_MAP_MAPPED) {
> > > +			iomap->type = IOMAP_MAPPED;
> > > +		} else if (map->m_flags & EXT4_MAP_UNWRITTEN) {
> > > +			iomap->type = IOMAP_UNWRITTEN;
> > > +		} else {
> > > +			WARN_ON_ONCE(1);
> > > +			return -EIO;
> > > +		}
> > > +		iomap->addr = (u64) map->m_pblk << blkbits;
> > > +	}
> > 
> > Looking at this function now, the 'type' argument looks a bit weird. Can we
> > perhaps just remove the 'type' argument and change the above to:
> 
> We can, but refer to the point below.
>  
> > 	if (map->m_flags & (EXT4_MAP_MAPPED | EXT4_MAP_UNWRITTEN)) {
> > 		if (map->m_flags & EXT4_MAP_MAPPED)
> > 			iomap->type = IOMAP_MAPPED;
> > 		else if (map->m_flags & EXT4_MAP_UNWRITTEN)
> > 			iomap->type = IOMAP_UNWRITTEN;
> > 		iomap->addr = (u64) map->m_pblk << blkbits;
> > 	} else {
> > 		iomap->type = IOMAP_HOLE;
> > 		iomap->addr = IOMAP_NULL_ADDR;
> > 	}
> > 
> > And then in ext4_iomap_begin() we overwrite the type to:
> > 
> > 	if (delalloc && iomap->type == IOMAP_HOLE)
> > 		iomap->type = IOMAP_DELALLOC;
> > 
> > That would IMO make ext4_set_iomap() arguments harder to get wrong.
> 
> I was thinking about this while doing a bunch of other things at work
> today. I'm kind of aligned with what Christoph mentioned around
> possibly duplicating some of the post 'iomap->type' setting from both
> current and any future ext4_set_iomap() callers. In addition to this,
> my thought was that if we're populating the iomap structure with
> values respectively, then it would make most sense to encapsulate
> those routines, if possible, within the ext4_set_iomap() as that's the
> sole purpose of the function.

Well, what I dislike about 'type' argument is the inconsistency in it's
handling. It is useful only for HOLE/DELALLOC, anything else will just give
you invalid iomap and you have to be careful to pass 0 in that case.

I understand the concern about possible duplication but since only
IOMAP_REPORT cares about IOMAP_DELALLOC, I'm not much concerned about it.
But another sensible API would be to optionally pass 'struct extent_status
*es' argument to ext4_set_iomap() and if this argument is non-NULL,
ext4_set_iomap() will handle the intersection of ext4_map_blocks and
extent_status and deduce appropriate resulting type from that.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03 11:32 [PATCH v4 0/8] ext4: port direct I/O to iomap infrastructure Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 1/8] ext4: move out iomap field population into separate helper Matthew Bobrowski
2019-10-08 10:27   ` Jan Kara
2019-10-09  8:57     ` Matthew Bobrowski
2019-10-09 13:06       ` Jan Kara [this message]
2019-10-10  5:39         ` Matthew Bobrowski
2019-10-09  6:02   ` Ritesh Harjani
2019-10-09  7:07     ` Christoph Hellwig
2019-10-09  7:50       ` Ritesh Harjani
2019-10-09  9:09         ` Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 2/8] ext4: move out IOMAP_WRITE path " Matthew Bobrowski
2019-10-08 10:31   ` Jan Kara
2019-10-09  9:18     ` Matthew Bobrowski
2019-10-09  6:22   ` Ritesh Harjani
2019-10-09  9:31     ` Matthew Bobrowski
2019-10-03 11:33 ` [PATCH v4 3/8] ext4: introduce new callback for IOMAP_REPORT operations Matthew Bobrowski
2019-10-08 10:42   ` Jan Kara
2019-10-09  9:41     ` Matthew Bobrowski
2019-10-09  6:00   ` Ritesh Harjani
2019-10-09 12:08     ` Matthew Bobrowski
2019-10-09 13:14       ` Ritesh Harjani
2019-10-03 11:34 ` [PATCH v4 4/8] ext4: introduce direct I/O read path using iomap infrastructure Matthew Bobrowski
2019-10-08 10:52   ` Jan Kara
2019-10-09 10:55     ` Matthew Bobrowski
2019-10-09  6:39   ` Ritesh Harjani
2019-10-03 11:34 ` [PATCH v4 5/8] ext4: move inode extension/truncate code out from ->iomap_end() callback Matthew Bobrowski
2019-10-08 11:25   ` Jan Kara
2019-10-09 10:18     ` Matthew Bobrowski
2019-10-09 12:51       ` Jan Kara
2019-10-10  5:44         ` Matthew Bobrowski
2019-10-09  6:27   ` Ritesh Harjani
2019-10-09 10:20     ` Matthew Bobrowski
2019-10-03 11:34 ` [PATCH v4 6/8] ext4: move inode extension checks out from ext4_iomap_alloc() Matthew Bobrowski
2019-10-08 11:27   ` Jan Kara
2019-10-09 10:21     ` Matthew Bobrowski
2019-10-09  6:30   ` Ritesh Harjani
2019-10-09 10:39     ` Matthew Bobrowski
2019-10-03 11:34 ` [PATCH v4 7/8] ext4: reorder map.m_flags checks in ext4_set_iomap() Matthew Bobrowski
2019-10-08 11:30   ` Jan Kara
2019-10-09 10:42     ` Matthew Bobrowski
2019-10-09  6:35   ` Ritesh Harjani
2019-10-09 10:43     ` Matthew Bobrowski
2019-10-03 11:35 ` [PATCH v4 8/8] ext4: introduce direct I/O write path using iomap infrastructure Matthew Bobrowski
2019-10-08 15:12   ` Jan Kara
2019-10-09  7:11     ` Christoph Hellwig
2019-10-09 13:41       ` Jan Kara
2019-10-09 11:53     ` Matthew Bobrowski

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