Re: [PATCH 5/9] btrfs: Use ->iomap_end() instead of btrfs_dio_data

[Christoph Hellwig <hch@infradead.org>]

On Thu, Mar 26, 2020 at 04:02:50PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> Use iomap->iomap_end() to check for failed or incomplete writes and call
> __endio_write_update_ordered(). We don't need btrfs_dio_data anymore so
> remove that. The bonus is we don't abuse current->journal_info anymore.
> 
> A new structure btrfs_iomap is used to keep a count of submitted I/O
> for writes.

I don't think you need a new structure.  As writes are limited to a
size_t (aka long) you can just case iomap->private.  That is a little
ugly, but we can just switch the private field to an union, something
like the patch below.  If I'm missing a reason why it has to be 64-bit
even on 32-bit kernels we can also grow the size a little on 32-bit
kernels, but right now I don't think that is needed unless I'm missing
something.

---
From e496cd3db3e7420050be19c5fe68e4675f5a2abc Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Fri, 27 Mar 2020 09:14:34 +0100
Subject: iomap: turn iomap->private into an union

Make using the union a little easier for scalar values.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/iomap.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 8b09463dae0d..61fea687d93d 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -85,7 +85,10 @@ struct iomap {
 	struct block_device	*bdev;	/* block device for I/O */
 	struct dax_device	*dax_dev; /* dax_dev for dax operations */
 	void			*inline_data;
-	void			*private; /* filesystem private */
+	union {				/* filesystem private data */
+		void		*ptr;
+		uintptr_t	uint;
+	} private;
 	const struct iomap_page_ops *page_ops;
 };
 
-- 
2.25.1