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iomap: use a srcmap for a read-modify-write I/O

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The srcmap is used to identify where the read is to be performed from.
It is passed to ->iomap_begin, which can fill it in if we need to read
data for partially written blocks from a different location than the
write target.  The srcmap is only supported for buffered writes so far.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
[hch: merged two patches, removed the IOMAP_F_COW flag, use iomap as
      srcmap if not set, adjust length down to srcmap end as well]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
This commit is contained in:
Goldwyn Rodrigues
2019-10-18 16:44:10 -07:00
committed by Darrick J. Wong
parent eb81cf9d0e
commit c039b99792
12 changed files with 82 additions and 55 deletions
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5
include/linux/iomap.h
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@@ -129,7 +129,8 @@ struct iomap_ops {
* The actual length is returned in iomap->length.
*/
int (*iomap_begin)(struct inode *inode, loff_t pos, loff_t length,
unsigned flags, struct iomap *iomap);
unsigned flags, struct iomap *iomap,
struct iomap *srcmap);
/*
* Commit and/or unreserve space previous allocated using iomap_begin.
@@ -145,7 +146,7 @@ struct iomap_ops {
* Main iomap iterator function.
*/
typedef loff_t (*iomap_actor_t)(struct inode *inode, loff_t pos, loff_t len,
void *data, struct iomap *iomap);
void *data, struct iomap *iomap, struct iomap *srcmap);
loff_t iomap_apply(struct inode *inode, loff_t pos, loff_t length,
unsigned flags, const struct iomap_ops *ops, void *data,