[05/13] btrfs: Add CoW in iomap based writes
diff mbox series

Message ID 20190802220048.16142-6-rgoldwyn@suse.de
State New
Headers show
Series
  • Btrfs iomap
Related show

Commit Message

Goldwyn Rodrigues Aug. 2, 2019, 10 p.m. UTC
From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Set iomap->type to IOMAP_COW and fill up the source map in case
the I/O is not page aligned.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/btrfs/iomap.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

Comments

Dave Chinner Aug. 5, 2019, 12:13 a.m. UTC | #1
On Fri, Aug 02, 2019 at 05:00:40PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> Set iomap->type to IOMAP_COW and fill up the source map in case
> the I/O is not page aligned.
.....
>  static void btrfs_buffered_page_done(struct inode *inode, loff_t pos,
>  		unsigned copied, struct page *page,
>  		struct iomap *iomap)
> @@ -188,6 +217,7 @@ static int btrfs_buffered_iomap_begin(struct inode *inode, loff_t pos,
>  	int ret;
>  	size_t write_bytes = length;
>  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> +	size_t end;
>  	size_t sector_offset = pos & (fs_info->sectorsize - 1);
>  	struct btrfs_iomap *bi;
>  
> @@ -255,6 +285,17 @@ static int btrfs_buffered_iomap_begin(struct inode *inode, loff_t pos,
>  	iomap->private = bi;
>  	iomap->length = round_up(write_bytes, fs_info->sectorsize);
>  	iomap->offset = round_down(pos, fs_info->sectorsize);
> +	end = pos + write_bytes;
> +	/* Set IOMAP_COW if start/end is not page aligned */
> +	if (((pos & (PAGE_SIZE - 1)) || (end & (PAGE_SIZE - 1)))) {
> +		iomap->type = IOMAP_COW;
> +		ret = get_iomap(inode, pos, length, srcmap);
> +		if (ret < 0)
> +			goto release;

I suspect you didn't test this case, because....

> +	} else {
> +		iomap->type = IOMAP_DELALLOC;
> +	}
> +
>  	iomap->addr = IOMAP_NULL_ADDR;
>  	iomap->type = IOMAP_DELALLOC;

The iomap->type is overwritten here and so IOMAP_COW will never be
seen by the iomap infrastructure...

Cheers,

Dave.
Goldwyn Rodrigues Aug. 22, 2019, 3:01 p.m. UTC | #2
On 10:13 05/08, Dave Chinner wrote:
> On Fri, Aug 02, 2019 at 05:00:40PM -0500, Goldwyn Rodrigues wrote:
> > From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > 
> > Set iomap->type to IOMAP_COW and fill up the source map in case
> > the I/O is not page aligned.
> .....
> >  static void btrfs_buffered_page_done(struct inode *inode, loff_t pos,
> >  		unsigned copied, struct page *page,
> >  		struct iomap *iomap)
> > @@ -188,6 +217,7 @@ static int btrfs_buffered_iomap_begin(struct inode *inode, loff_t pos,
> >  	int ret;
> >  	size_t write_bytes = length;
> >  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > +	size_t end;
> >  	size_t sector_offset = pos & (fs_info->sectorsize - 1);
> >  	struct btrfs_iomap *bi;
> >  
> > @@ -255,6 +285,17 @@ static int btrfs_buffered_iomap_begin(struct inode *inode, loff_t pos,
> >  	iomap->private = bi;
> >  	iomap->length = round_up(write_bytes, fs_info->sectorsize);
> >  	iomap->offset = round_down(pos, fs_info->sectorsize);
> > +	end = pos + write_bytes;
> > +	/* Set IOMAP_COW if start/end is not page aligned */
> > +	if (((pos & (PAGE_SIZE - 1)) || (end & (PAGE_SIZE - 1)))) {
> > +		iomap->type = IOMAP_COW;
> > +		ret = get_iomap(inode, pos, length, srcmap);
> > +		if (ret < 0)
> > +			goto release;
> 
> I suspect you didn't test this case, because....
> 
> > +	} else {
> > +		iomap->type = IOMAP_DELALLOC;
> > +	}
> > +
> >  	iomap->addr = IOMAP_NULL_ADDR;
> >  	iomap->type = IOMAP_DELALLOC;
> 
> The iomap->type is overwritten here and so IOMAP_COW will never be
> seen by the iomap infrastructure...

Yes, thats correct. I will fix this.

Patch
diff mbox series

diff --git a/fs/btrfs/iomap.c b/fs/btrfs/iomap.c
index 9eb5e7b7603a..879038e2f1a0 100644
--- a/fs/btrfs/iomap.c
+++ b/fs/btrfs/iomap.c
@@ -165,6 +165,35 @@  static int btrfs_find_new_delalloc_bytes(struct btrfs_inode *inode,
 	return 0;
 }
 
+/*
+ * get_iomap: Get the block map and fill the iomap structure
+ * @pos: file position
+ * @length: I/O length
+ * @iomap: The iomap structure to fill
+ */
+
+static int get_iomap(struct inode *inode, loff_t pos, loff_t length,
+		struct iomap *iomap)
+{
+	struct extent_map *em;
+	iomap->addr = IOMAP_NULL_ADDR;
+	em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, pos, length, 0);
+	if (IS_ERR(em))
+		return PTR_ERR(em);
+	/* XXX Do we need to check for em->flags here? */
+	if (em->block_start == EXTENT_MAP_HOLE) {
+		iomap->type = IOMAP_HOLE;
+	} else {
+		iomap->addr = em->block_start;
+		iomap->type = IOMAP_MAPPED;
+	}
+	iomap->offset = em->start;
+	iomap->bdev = em->bdev;
+	iomap->length = em->len;
+	free_extent_map(em);
+	return 0;
+}
+
 static void btrfs_buffered_page_done(struct inode *inode, loff_t pos,
 		unsigned copied, struct page *page,
 		struct iomap *iomap)
@@ -188,6 +217,7 @@  static int btrfs_buffered_iomap_begin(struct inode *inode, loff_t pos,
 	int ret;
 	size_t write_bytes = length;
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	size_t end;
 	size_t sector_offset = pos & (fs_info->sectorsize - 1);
 	struct btrfs_iomap *bi;
 
@@ -255,6 +285,17 @@  static int btrfs_buffered_iomap_begin(struct inode *inode, loff_t pos,
 	iomap->private = bi;
 	iomap->length = round_up(write_bytes, fs_info->sectorsize);
 	iomap->offset = round_down(pos, fs_info->sectorsize);
+	end = pos + write_bytes;
+	/* Set IOMAP_COW if start/end is not page aligned */
+	if (((pos & (PAGE_SIZE - 1)) || (end & (PAGE_SIZE - 1)))) {
+		iomap->type = IOMAP_COW;
+		ret = get_iomap(inode, pos, length, srcmap);
+		if (ret < 0)
+			goto release;
+	} else {
+		iomap->type = IOMAP_DELALLOC;
+	}
+
 	iomap->addr = IOMAP_NULL_ADDR;
 	iomap->type = IOMAP_DELALLOC;
 	iomap->bdev = fs_info->fs_devices->latest_bdev;