erofs: tidy up z_erofs_lz4_decompress

To prepare for the upcoming ztailpacking feature and further
cleanups, introduce a unique z_erofs_lz4_decompress_ctx to keep
the context, including inpages, outpages and oend, which are
frequently used by the lz4 decompressor.

No logic changes.

Link: https://lore.kernel.org/r/20211228054604.114518-2-hsiangkao@linux.alibaba.comReviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/decompressor.c

@@ -16,6 +16,14 @@
 #define LZ4_DECOMPRESS_INPLACE_MARGIN(srcsize)  (((srcsize) >> 8) + 32)
 #endif
 
+struct z_erofs_lz4_decompress_ctx {
+	struct z_erofs_decompress_req *rq;
+	/* # of encoded, decoded pages */
+	unsigned int inpages, outpages;
+	/* decoded block total length (used for in-place decompression) */
+	unsigned int oend;
+};
+
 int z_erofs_load_lz4_config(struct super_block *sb,
 			    struct erofs_super_block *dsb,
 			    struct z_erofs_lz4_cfgs *lz4, int size)
@@ -56,11 +64,10 @@ int z_erofs_load_lz4_config(struct super_block *sb,
  * Fill all gaps with bounce pages if it's a sparse page list. Also check if
  * all physical pages are consecutive, which can be seen for moderate CR.
  */
-static int z_erofs_lz4_prepare_dstpages(struct z_erofs_decompress_req *rq,
+static int z_erofs_lz4_prepare_dstpages(struct z_erofs_lz4_decompress_ctx *ctx,
 					struct page **pagepool)
 {
-	const unsigned int nr =
-		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
+	struct z_erofs_decompress_req *rq = ctx->rq;
 	struct page *availables[LZ4_MAX_DISTANCE_PAGES] = { NULL };
 	unsigned long bounced[DIV_ROUND_UP(LZ4_MAX_DISTANCE_PAGES,
 					   BITS_PER_LONG)] = { 0 };
@@ -70,7 +77,7 @@ static int z_erofs_lz4_prepare_dstpages(struct z_erofs_decompress_req *rq,
 	unsigned int i, j, top;
 
 	top = 0;
-	for (i = j = 0; i < nr; ++i, ++j) {
+	for (i = j = 0; i < ctx->outpages; ++i, ++j) {
 		struct page *const page = rq->out[i];
 		struct page *victim;
 
@@ -112,41 +119,36 @@ static int z_erofs_lz4_prepare_dstpages(struct z_erofs_decompress_req *rq,
 	return kaddr ? 1 : 0;
 }
 
-static void *z_erofs_lz4_handle_inplace_io(struct z_erofs_decompress_req *rq,
+static void *z_erofs_lz4_handle_overlap(struct z_erofs_lz4_decompress_ctx *ctx,
 			void *inpage, unsigned int *inputmargin, int *maptype,
 			bool support_0padding)
 {
-	unsigned int nrpages_in, nrpages_out;
-	unsigned int ofull, oend, inputsize, total, i, j;
+	struct z_erofs_decompress_req *rq = ctx->rq;
+	unsigned int omargin, total, i, j;
 	struct page **in;
 	void *src, *tmp;
 
-	inputsize = rq->inputsize;
-	nrpages_in = PAGE_ALIGN(inputsize) >> PAGE_SHIFT;
-	oend = rq->pageofs_out + rq->outputsize;
-	ofull = PAGE_ALIGN(oend);
-	nrpages_out = ofull >> PAGE_SHIFT;
-
 	if (rq->inplace_io) {
+		omargin = PAGE_ALIGN(ctx->oend) - ctx->oend;
 		if (rq->partial_decoding || !support_0padding ||
-		    ofull - oend < LZ4_DECOMPRESS_INPLACE_MARGIN(inputsize))
+		    omargin < LZ4_DECOMPRESS_INPLACE_MARGIN(rq->inputsize))
 			goto docopy;
 
-		for (i = 0; i < nrpages_in; ++i) {
+		for (i = 0; i < ctx->inpages; ++i) {
 			DBG_BUGON(rq->in[i] == NULL);
-			for (j = 0; j < nrpages_out - nrpages_in + i; ++j)
+			for (j = 0; j < ctx->outpages - ctx->inpages + i; ++j)
 				if (rq->out[j] == rq->in[i])
 					goto docopy;
 		}
 	}
 
-	if (nrpages_in <= 1) {
+	if (ctx->inpages <= 1) {
 		*maptype = 0;
 		return inpage;
 	}
 	kunmap_atomic(inpage);
 	might_sleep();
-	src = erofs_vm_map_ram(rq->in, nrpages_in);
+	src = erofs_vm_map_ram(rq->in, ctx->inpages);
 	if (!src)
 		return ERR_PTR(-ENOMEM);
 	*maptype = 1;
@@ -155,7 +157,7 @@ static void *z_erofs_lz4_handle_inplace_io(struct z_erofs_decompress_req *rq,
 docopy:
 	/* Or copy compressed data which can be overlapped to per-CPU buffer */
 	in = rq->in;
-	src = erofs_get_pcpubuf(nrpages_in);
+	src = erofs_get_pcpubuf(ctx->inpages);
 	if (!src) {
 		DBG_BUGON(1);
 		kunmap_atomic(inpage);
@@ -182,9 +184,10 @@ static void *z_erofs_lz4_handle_inplace_io(struct z_erofs_decompress_req *rq,
 	return src;
 }
 
-static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq,
+static int z_erofs_lz4_decompress_mem(struct z_erofs_lz4_decompress_ctx *ctx,
 				      u8 *out)
 {
+	struct z_erofs_decompress_req *rq = ctx->rq;
 	unsigned int inputmargin;
 	u8 *headpage, *src;
 	bool support_0padding;
@@ -210,8 +213,8 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq,
 	}
 
 	rq->inputsize -= inputmargin;
-	src = z_erofs_lz4_handle_inplace_io(rq, headpage, &inputmargin,
-					    &maptype, support_0padding);
+	src = z_erofs_lz4_handle_overlap(ctx, headpage, &inputmargin,
+					 &maptype, support_0padding);
 	if (IS_ERR(src))
 		return PTR_ERR(src);
 
@@ -240,9 +243,9 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq,
 	}
 
 	if (maptype == 0) {
-		kunmap_atomic(src);
+		kunmap_atomic(headpage);
 	} else if (maptype == 1) {
-		vm_unmap_ram(src, PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT);
+		vm_unmap_ram(src, ctx->inpages);
 	} else if (maptype == 2) {
 		erofs_put_pcpubuf(src);
 	} else {
@@ -255,14 +258,18 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq,
 static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
 				  struct page **pagepool)
 {
-	const unsigned int nrpages_out =
-		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
+	struct z_erofs_lz4_decompress_ctx ctx;
 	unsigned int dst_maptype;
 	void *dst;
 	int ret;
 
+	ctx.rq = rq;
+	ctx.oend = rq->pageofs_out + rq->outputsize;
+	ctx.outpages = PAGE_ALIGN(ctx.oend) >> PAGE_SHIFT;
+	ctx.inpages = PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT;
+
 	/* one optimized fast path only for non bigpcluster cases yet */
-	if (rq->inputsize <= PAGE_SIZE && nrpages_out == 1 && !rq->inplace_io) {
+	if (ctx.inpages == 1 && ctx.outpages == 1 && !rq->inplace_io) {
 		DBG_BUGON(!*rq->out);
 		dst = kmap_atomic(*rq->out);
 		dst_maptype = 0;
@@ -270,27 +277,25 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
 	}
 
 	/* general decoding path which can be used for all cases */
-	ret = z_erofs_lz4_prepare_dstpages(rq, pagepool);
-	if (ret < 0)
+	ret = z_erofs_lz4_prepare_dstpages(&ctx, pagepool);
+	if (ret < 0) {
 		return ret;
-	if (ret) {
+	} else if (ret > 0) {
 		dst = page_address(*rq->out);
 		dst_maptype = 1;
-		goto dstmap_out;
+	} else {
+		dst = erofs_vm_map_ram(rq->out, ctx.outpages);
+		if (!dst)
+			return -ENOMEM;
+		dst_maptype = 2;
 	}
 
-	dst = erofs_vm_map_ram(rq->out, nrpages_out);
-	if (!dst)
-		return -ENOMEM;
-	dst_maptype = 2;
-
 dstmap_out:
-	ret = z_erofs_lz4_decompress_mem(rq, dst + rq->pageofs_out);
-
+	ret = z_erofs_lz4_decompress_mem(&ctx, dst + rq->pageofs_out);
 	if (!dst_maptype)
 		kunmap_atomic(dst);
 	else if (dst_maptype == 2)
-		vm_unmap_ram(dst, nrpages_out);
+		vm_unmap_ram(dst, ctx.outpages);
 	return ret;
 }