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From: "Darrick J. Wong" <djwong@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Andreas Gruenbacher <agruenba@redhat.com>,
	Shiyang Ruan <ruansy.fnst@fujitsu.com>,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-btrfs@vger.kernel.org, nvdimm@lists.linux.dev,
	cluster-devel@redhat.com
Subject: Re: [PATCH 19/30] iomap: switch iomap_bmap to use iomap_iter
Date: Mon, 9 Aug 2021 23:39:51 -0700	[thread overview]
Message-ID: <20210810063951.GH3601443@magnolia> (raw)
In-Reply-To: <20210809061244.1196573-20-hch@lst.de>

On Mon, Aug 09, 2021 at 08:12:33AM +0200, Christoph Hellwig wrote:
> Rewrite the ->bmap implementation based on iomap_iter.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/fiemap.c | 31 +++++++++++++------------------
>  1 file changed, 13 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/iomap/fiemap.c b/fs/iomap/fiemap.c
> index acad09a8c188df..60daadba16c149 100644
> --- a/fs/iomap/fiemap.c
> +++ b/fs/iomap/fiemap.c
> @@ -92,35 +92,30 @@ int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,
>  }
>  EXPORT_SYMBOL_GPL(iomap_fiemap);
>  
> -static loff_t
> -iomap_bmap_actor(struct inode *inode, loff_t pos, loff_t length,
> -		void *data, struct iomap *iomap, struct iomap *srcmap)
> -{
> -	sector_t *bno = data, addr;
> -
> -	if (iomap->type == IOMAP_MAPPED) {
> -		addr = (pos - iomap->offset + iomap->addr) >> inode->i_blkbits;
> -		*bno = addr;
> -	}
> -	return 0;
> -}
> -
>  /* legacy ->bmap interface.  0 is the error return (!) */
>  sector_t
>  iomap_bmap(struct address_space *mapping, sector_t bno,
>  		const struct iomap_ops *ops)
>  {
> -	struct inode *inode = mapping->host;
> -	loff_t pos = bno << inode->i_blkbits;
> -	unsigned blocksize = i_blocksize(inode);
> +	struct iomap_iter iter = {
> +		.inode	= mapping->host,
> +		.pos	= (loff_t)bno << mapping->host->i_blkbits,
> +		.len	= i_blocksize(mapping->host),
> +		.flags	= IOMAP_REPORT,
> +	};
>  	int ret;
>  
>  	if (filemap_write_and_wait(mapping))
>  		return 0;
>  
>  	bno = 0;
> -	ret = iomap_apply(inode, pos, blocksize, 0, ops, &bno,
> -			  iomap_bmap_actor);
> +	while ((ret = iomap_iter(&iter, ops)) > 0) {
> +		if (iter.iomap.type != IOMAP_MAPPED)
> +			continue;

I still feel uncomfortable about this use of "continue" here, because it
really means "call iomap_iter again to clean up and exit even though we
know it won't even look for more iomaps to iterate".

To me that feels subtly broken (I usually associate 'continue' with
'go run the loop body again'), and even though bmap has been a quirky
hot mess for 45 years, we don't need to make it even moreso.

Can't this at least be rephrased as:

	const uint bno_shift = (mapping->host->i_blkbits - SECTOR_SHIFT);

	while ((ret = iomap_iter(&iter, ops)) > 0) {
		if (iter.iomap.type == IOMAP_MAPPED)
			bno = iomap_sector(iomap, iter.pos) << bno_shift;
		/* leave iter.processed unset to stop iteration */
	}

to make the loop exit more explicit?

--D

> +		bno = (iter.pos - iter.iomap.offset + iter.iomap.addr) >>
> +				mapping->host->i_blkbits;
> +	}
> +
>  	if (ret)
>  		return 0;
>  	return bno;
> -- 
> 2.30.2
> 

  reply	other threads:[~2021-08-10  6:39 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09  6:12 switch iomap to an iterator model v2 Christoph Hellwig
2021-08-09  6:12 ` [PATCH 01/30] iomap: fix a trivial comment typo in trace.h Christoph Hellwig
2021-08-09  6:12 ` [PATCH 02/30] iomap: remove the iomap arguments to ->page_{prepare,done} Christoph Hellwig
2021-08-09  6:12 ` [PATCH 03/30] iomap: mark the iomap argument to iomap_sector const Christoph Hellwig
2021-08-09  6:12 ` [PATCH 04/30] iomap: mark the iomap argument to iomap_inline_data const Christoph Hellwig
2021-08-09 16:17   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 05/30] iomap: mark the iomap argument to iomap_inline_data_valid const Christoph Hellwig
2021-08-09 16:17   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 06/30] fs: mark the iomap argument to __block_write_begin_int const Christoph Hellwig
2021-08-09  6:12 ` [PATCH 07/30] fsdax: mark the iomap argument to dax_iomap_sector as const Christoph Hellwig
2021-08-19 20:35   ` Dan Williams
2021-08-09  6:12 ` [PATCH 08/30] iomap: mark the iomap argument to iomap_read_inline_data const Christoph Hellwig
2021-08-09  6:12 ` [PATCH 09/30] iomap: mark the iomap argument to iomap_read_page_sync const Christoph Hellwig
2021-08-09  6:12 ` [PATCH 10/30] iomap: fix the iomap_readpage_actor return value for inline data Christoph Hellwig
2021-08-10 23:31   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 11/30] iomap: add the new iomap_iter model Christoph Hellwig
2021-08-09 22:10   ` Dave Chinner
2021-08-10  6:45     ` Darrick J. Wong
2021-08-10  7:13       ` Christoph Hellwig
2021-08-11  0:31   ` Darrick J. Wong
2021-08-11  5:38     ` Christoph Hellwig
2021-08-11 19:17       ` Darrick J. Wong
2021-08-12  6:49         ` Christoph Hellwig
2021-08-12 18:20           ` Darrick J. Wong
2021-08-13  7:29             ` Christoph Hellwig
2021-08-11 19:17   ` [PATCH v2.1 " Darrick J. Wong
2021-08-17  2:34     ` Dave Chinner
2021-08-19 21:25   ` [PATCH " Dan Williams
2021-08-20  4:11     ` Christoph Hellwig
2021-08-20 15:27       ` Dan Williams
2021-08-09  6:12 ` [PATCH 12/30] iomap: switch readahead and readpage to use iomap_iter Christoph Hellwig
2021-08-10 23:46   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 13/30] iomap: switch iomap_file_buffered_write " Christoph Hellwig
2021-08-10 23:53   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 14/30] iomap: switch iomap_file_unshare " Christoph Hellwig
2021-08-10 23:54   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 15/30] iomap: switch iomap_zero_range " Christoph Hellwig
2021-08-10 23:54   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 16/30] iomap: switch iomap_page_mkwrite " Christoph Hellwig
2021-08-10 23:58   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 17/30] iomap: switch __iomap_dio_rw " Christoph Hellwig
2021-08-11  0:17   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 18/30] iomap: switch iomap_fiemap " Christoph Hellwig
2021-08-11  0:05   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 19/30] iomap: switch iomap_bmap " Christoph Hellwig
2021-08-10  6:39   ` Darrick J. Wong [this message]
2021-08-10  7:13     ` Christoph Hellwig
2021-08-11 19:18   ` [PATCH v2.1 " Darrick J. Wong
2021-08-12  6:50     ` Christoph Hellwig
2021-08-17  2:35     ` Dave Chinner
2021-08-09  6:12 ` [PATCH 20/30] iomap: switch iomap_seek_hole " Christoph Hellwig
2021-08-11  0:13   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 21/30] iomap: switch iomap_seek_data " Christoph Hellwig
2021-08-11  0:12   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 22/30] iomap: switch iomap_swapfile_activate " Christoph Hellwig
2021-08-11  0:08   ` Darrick J. Wong
2021-08-09  6:12 ` [PATCH 23/30] fsdax: switch dax_iomap_rw " Christoph Hellwig
2021-08-11  0:07   ` Darrick J. Wong
2021-08-19 21:55   ` Dan Williams
2021-08-09  6:12 ` [PATCH 24/30] iomap: remove iomap_apply Christoph Hellwig
2021-08-11 19:18   ` [PATCH v2.1 " Darrick J. Wong
2021-08-17  2:36     ` Dave Chinner
2021-08-09  6:12 ` [PATCH 25/30] iomap: pass an iomap_iter to various buffered I/O helpers Christoph Hellwig
2021-08-09  6:12 ` [PATCH 26/30] iomap: rework unshare flag Christoph Hellwig
2021-08-09  6:12 ` [PATCH 27/30] fsdax: factor out helpers to simplify the dax fault code Christoph Hellwig
2021-08-09  6:12 ` [PATCH 28/30] fsdax: factor out a dax_fault_actor() helper Christoph Hellwig
2021-08-09  6:12 ` [PATCH 29/30] fsdax: switch the fault handlers to use iomap_iter Christoph Hellwig
2021-08-09  6:12 ` [PATCH 30/30] iomap: constify iomap_iter_srcmap Christoph Hellwig
2021-08-11 19:19 ` [PATCH 31/30] iomap: move iomap iteration code to iter.c Darrick J. Wong
2021-08-17  2:37   ` Dave Chinner

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