[PATCH 05/15] btrfs: Add CoW in iomap based writes

Goldwyn Rodrigues
2019-09-05T15:07:09Z

Set iomap->flags to IOMAP_F_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 | 42 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/iomap.c b/fs/btrfs/iomap.c
index 025ccbf471bf..f8fa34105838 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)
@@ -190,6 +219,7 @@ 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;

@@ -257,8 +287,18 @@ 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_F_COW if start/end is not page aligned */
+ if (((pos & (PAGE_SIZE - 1)) || (end & (PAGE_SIZE - 1)))) {
+ iomap->flags = IOMAP_F_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;
iomap->page_ops = &btrfs_buffered_page_ops;
return 0;
--
2.16.4