[PATCH 2/7] fsdax: Introduce dax_copy_edges() for CoW

Shiyang Ruan
2021-02-07T17:09:41Z

dax_copy_edges() is a helper functions performs a copy from one part of
the device to another for data not page aligned.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
---
fs/dax.c | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

diff --git a/fs/dax.c b/fs/dax.c
index b012b2db7ba2..ea4e8a434900 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1038,6 +1038,47 @@ static int dax_iomap_direct_access(struct iomap *iomap, loff_t pos, size_t size,
return rc;
}

+/*
+ * Copies the part of the pages not included in the write, but required for CoW
+ * because offset/offset+length are not page aligned.
+ */
+static int dax_copy_edges(loff_t pos, loff_t length, struct iomap *srcmap,
+ void *daddr, bool pmd)
+{
+ size_t page_size = pmd ? PMD_SIZE : PAGE_SIZE;
+ loff_t offset = pos & (page_size - 1);
+ size_t size = ALIGN(offset + length, page_size);
+ loff_t end = pos + length;
+ loff_t pg_end = round_up(end, page_size);
+ void *saddr = 0;
+ int ret = 0;
+
+ ret = dax_iomap_direct_access(srcmap, pos, size, &saddr, NULL);
+ if (ret)
+ return ret;
+ /*
+ * Copy the first part of the page
+ * Note: we pass offset as length
+ */
+ if (offset) {
+ if (saddr)
+ ret = copy_mc_to_kernel(daddr, saddr, offset);
+ else
+ memset(daddr, 0, offset);
+ }
+
+ /* Copy the last part of the range */
+ if (end < pg_end) {
+ if (saddr)
+ ret = copy_mc_to_kernel(daddr + offset + length,
+ saddr + offset + length, pg_end - end);
+ else
+ memset(daddr + offset + length, 0, pg_end - end);
+ }
+
+ return ret;
+}
+
/*
* The user has performed a load from a hole in the file. Allocating a new
* page in the file would cause excessive storage usage for workloads with
--
2.30.0