[RFC PATCH v2] erofs: support uncompressed pcluster with more than 1 block

[Yue Hu <zbestahu@gmail.com>]

From: Yue Hu <huyue2@coolpad.com>

The length of uncompressed pcluster may exceed one block in some new
scenarios such as non 4K-sized lcluster (which will be supported later).
So, let's support the decompression for this firstly.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
---
v2: fix tail data length.

 fs/erofs/decompressor.c | 64 ++++++++++++++++++++++++++---------------
 1 file changed, 41 insertions(+), 23 deletions(-)

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 2d55569f96ac..77d2b6cb6eda 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -320,41 +320,59 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
 static int z_erofs_shifted_transform(struct z_erofs_decompress_req *rq,
 				     struct page **pagepool)
 {
+	const unsigned int nrpages_in = rq->inputsize >> PAGE_SHIFT;
 	const unsigned int nrpages_out =
 		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
-	const unsigned int righthalf = min_t(unsigned int, rq->outputsize,
-					     PAGE_SIZE - rq->pageofs_out);
-	const unsigned int lefthalf = rq->outputsize - righthalf;
+	unsigned int righthalf, lefthalf, i;
 	unsigned char *src, *dst;
 
-	if (nrpages_out > 2) {
+	if (nrpages_in == 1 && nrpages_out > 2) {
 		DBG_BUGON(1);
 		return -EIO;
 	}
 
-	if (rq->out[0] == *rq->in) {
-		DBG_BUGON(nrpages_out != 1);
-		return 0;
-	}
+	i = 0;
+	do {
+		unsigned int outputsize = rq->outputsize;
+
+		righthalf = min_t(unsigned int, outputsize,
+				  PAGE_SIZE - rq->pageofs_out);
+		lefthalf = min_t(unsigned int, outputsize - righthalf,
+				 PAGE_SIZE - righthalf);
+
+		src = kmap_atomic(rq->in[i]) + rq->pageofs_in;
+		if (rq->out[i]) {
+			if (rq->out[i] == rq->in[i]) {
+				DBG_BUGON(nrpages_in == 1 && nrpages_out != 1);
+			} else {
+				dst = kmap_atomic(rq->out[i]);
+				memcpy(dst + rq->pageofs_out, src, righthalf);
+				kunmap_atomic(dst);
+			}
+		}
 
-	src = kmap_atomic(*rq->in) + rq->pageofs_in;
-	if (rq->out[0]) {
-		dst = kmap_atomic(rq->out[0]);
-		memcpy(dst + rq->pageofs_out, src, righthalf);
-		kunmap_atomic(dst);
-	}
+		if (i + 1 == nrpages_out) {
+			kunmap_atomic(src);
+			break;
+		}
 
-	if (nrpages_out == 2) {
-		DBG_BUGON(!rq->out[1]);
-		if (rq->out[1] == *rq->in) {
-			memmove(src, src + righthalf, lefthalf);
+		if (rq->out[i + 1]) {
+			if (rq->out[i + 1] == rq->in[i]) {
+				memmove(src, src + righthalf, lefthalf);
+			} else {
+				dst = kmap_atomic(rq->out[i + 1]);
+				memcpy(dst, src + righthalf, lefthalf);
+				kunmap_atomic(dst);
+			}
 		} else {
-			dst = kmap_atomic(rq->out[1]);
-			memcpy(dst, src + righthalf, lefthalf);
-			kunmap_atomic(dst);
+			DBG_BUGON(nrpages_in == 1 && nrpages_out == 2);
 		}
-	}
-	kunmap_atomic(src);
+		kunmap_atomic(src);
+
+		if (outputsize > PAGE_SIZE)
+			outputsize -= PAGE_SIZE;
+	} while (++i < nrpages_in);
+
 	return 0;
 }
 
-- 
2.17.1