[PATCH 06/15] btrfs: Add CoW in iomap based writes

[Goldwyn Rodrigues]

From: Goldwyn Rodrigues <rgold...@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 <rgold...@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..8ed93d427962 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_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;
        iomap->page_ops = &btrfs_buffered_page_ops;
        return 0;
-- 
2.16.4