From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
The IOMAP_F_COW is a flag to notify dax that it needs to copy
the data from iomap->cow_addr to iomap->addr, if the start/end
of I/O are not page aligned.
This also introduces dax_to_dax_copy() which performs a copy
from one part of the device to another, to a maximum of one page.
Question: Using iomap.cow_addr == 0 means the CoW is to be copied
(or memset) from a hole. Would this be better handled through a flag?
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
fs/dax.c | 36 ++++++++++++++++++++++++++++++++++++
include/linux/iomap.h | 3 +++
2 files changed, 39 insertions(+)
diff --git a/fs/dax.c b/fs/dax.c
index ca0671d55aa6..e254535dd830 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1051,6 +1051,28 @@ static bool dax_range_is_aligned(struct block_device *bdev,
return true;
}
+static void dax_to_dax_copy(struct iomap *iomap, loff_t pos, void *daddr,
+ size_t len)
+{
+ loff_t blk_start, blk_pg;
+ void *saddr;
+ ssize_t map_len;
+
+ /* A zero address is a hole. */
+ if (iomap->cow_addr == 0) {
+ memset(daddr, 0, len);
+ return;
+ }
+
+ blk_start = iomap->cow_addr + pos - iomap->cow_pos;
+ blk_pg = round_down(blk_start, PAGE_SIZE);
+
+ map_len = dax_direct_access(iomap->dax_dev, PHYS_PFN(blk_pg), PAGE_SIZE,
+ &saddr, NULL);
+ saddr += blk_start - blk_pg;
+ memcpy(daddr, saddr, len);
+}
+
int __dax_zero_page_range(struct block_device *bdev,
struct dax_device *dax_dev, sector_t sector,
unsigned int offset, unsigned int size)
@@ -1143,6 +1165,20 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
break;
}
+ if (iomap->flags & IOMAP_F_COW) {
+ loff_t pg_end = round_up(end, PAGE_SIZE);
+ /*
+ * Copy the first part of the page
+ * Note: we pass offset as length
+ */
+ if (offset)
+ dax_to_dax_copy(iomap, pos - offset, kaddr, offset);
+
+ /* Copy the last part of the range */
+ if (end < pg_end)
+ dax_to_dax_copy(iomap, end, kaddr + offset + length, pg_end - end);
+ }
+
map_len = PFN_PHYS(map_len);
kaddr += offset;
map_len -= offset;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 0fefb5455bda..391785de1428 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -35,6 +35,7 @@ struct vm_fault;
#define IOMAP_F_NEW 0x01 /* blocks have been newly allocated */
#define IOMAP_F_DIRTY 0x02 /* uncommitted metadata */
#define IOMAP_F_BUFFER_HEAD 0x04 /* file system requires buffer heads */
+#define IOMAP_F_COW 0x08 /* cow before write */
/*
* Flags that only need to be reported for IOMAP_REPORT requests:
@@ -59,6 +60,8 @@ struct iomap {
u64 length; /* length of mapping, bytes */
u16 type; /* type of mapping */
u16 flags; /* flags for mapping */
+ u64 cow_addr; /* read address to perform CoW */
+ loff_t cow_pos; /* file offset of cow_addr */
struct block_device *bdev; /* block device for I/O */
struct dax_device *dax_dev; /* dax_dev for dax operations */
void *inline_data;
--
2.16.4
