From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
The IOMAP_DAX_COW is a iomap type which performs copy of
edges of data while performing a write if start/end are
not page aligned. The source address is expected in
iomap->inline_data.
dax_copy_edges() is a helper functions performs a copy from
one part of the device to another for data not page aligned.
If iomap->inline_data is NULL, it memset's the area to zero.
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
fs/dax.c | 41 ++++++++++++++++++++++++++++++++++++++++-
include/linux/iomap.h | 1 +
2 files changed, 41 insertions(+), 1 deletion(-)
diff --git a/fs/dax.c b/fs/dax.c
index ca0671d55aa6..4b4ac51fbd16 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1083,6 +1083,40 @@ int __dax_zero_page_range(struct block_device *bdev,
}
EXPORT_SYMBOL_GPL(__dax_zero_page_range);
+/*
+ * dax_copy_edges - Copies the part of the pages not included in
+ * the write, but required for CoW because
+ * offset/offset+length are not page aligned.
+ */
+static void dax_copy_edges(struct inode *inode, loff_t pos, loff_t length,
+ struct iomap *iomap, void *daddr)
+{
+ unsigned offset = pos & (PAGE_SIZE - 1);
+ loff_t end = pos + length;
+ loff_t pg_end = round_up(end, PAGE_SIZE);
+ void *saddr = iomap->inline_data;
+ /*
+ * Copy the first part of the page
+ * Note: we pass offset as length
+ */
+ if (offset) {
+ if (saddr)
+ memcpy(daddr, saddr, offset);
+ else
+ memset(daddr, 0, offset);
+ }
+
+ /* Copy the last part of the range */
+ if (end < pg_end) {
+ if (saddr)
+ memcpy(daddr + offset + length,
+ saddr + offset + length, pg_end - end);
+ else
+ memset(daddr + offset + length, 0,
+ pg_end - end);
+ }
+}
+
static loff_t
dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
struct iomap *iomap)
@@ -1104,9 +1138,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
return iov_iter_zero(min(length, end - pos), iter);
}
- if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
+ if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED
+ && iomap->type != IOMAP_DAX_COW))
return -EIO;
+
/*
* Write can allocate block for an area which has a hole page mapped
* into page tables. We have to tear down these mappings so that data
@@ -1143,6 +1179,9 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
break;
}
+ if (iomap->type == IOMAP_DAX_COW)
+ dax_copy_edges(inode, pos, length, iomap, kaddr);
+
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..6e885c5a38a3 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -25,6 +25,7 @@ struct vm_fault;
#define IOMAP_MAPPED 0x03 /* blocks allocated at @addr */
#define IOMAP_UNWRITTEN 0x04 /* blocks allocated at @addr in unwritten state */
#define IOMAP_INLINE 0x05 /* data inline in the inode */
+#define IOMAP_DAX_COW 0x06 /* Copy data pointed by inline_data before write*/
/*
* Flags for all iomap mappings:
--
2.16.4
