[PATCH 2/2] erofs: simplify z_erofs_transform_plain()

[Gao Xiang]

Use memcpy_to_page() instead of open-coding them.

In addition, add a missing flush_dcache_page() even though almost all
modern architectures clear `PG_dcache_clean` flag for new file cache
pages so that it doesn't change anything in practice.

Signed-off-by: Gao Xiang <hsiang...@linux.alibaba.com>
---
preliminary tested with silesia dataset.

 fs/erofs/decompressor.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index ad53cf52d899..cfad1eac7fd9 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -328,7 +328,7 @@ static int z_erofs_transform_plain(struct 
z_erofs_decompress_req *rq,
        const unsigned int lefthalf = rq->outputsize - righthalf;
        const unsigned int interlaced_offset =
                rq->alg == Z_EROFS_COMPRESSION_SHIFTED ? 0 : rq->pageofs_out;
-       unsigned char *src, *dst;
+       u8 *src;
 
        if (outpages > 2 && rq->alg == Z_EROFS_COMPRESSION_SHIFTED) {
                DBG_BUGON(1);
@@ -341,22 +341,19 @@ static int z_erofs_transform_plain(struct 
z_erofs_decompress_req *rq,
        }
 
        src = kmap_local_page(rq->in[inpages - 1]) + rq->pageofs_in;
-       if (rq->out[0]) {
-               dst = kmap_local_page(rq->out[0]);
-               memcpy(dst + rq->pageofs_out, src + interlaced_offset,
-                      righthalf);
-               kunmap_local(dst);
-       }
+       if (rq->out[0])
+               memcpy_to_page(rq->out[0], rq->pageofs_out,
+                              src + interlaced_offset, righthalf);
 
        if (outpages > inpages) {
                DBG_BUGON(!rq->out[outpages - 1]);
                if (rq->out[outpages - 1] != rq->in[inpages - 1]) {
-                       dst = kmap_local_page(rq->out[outpages - 1]);
-                       memcpy(dst, interlaced_offset ? src :
-                                       (src + righthalf), lefthalf);
-                       kunmap_local(dst);
+                       memcpy_to_page(rq->out[outpages - 1], 0, src +
+                                       (interlaced_offset ? 0 : righthalf),
+                                      lefthalf);
                } else if (!interlaced_offset) {
                        memmove(src, src + righthalf, lefthalf);
+                       flush_dcache_page(rq->in[inpages - 1]);
                }
        }
        kunmap_local(src);
-- 
2.24.4