zram: add dictionary support to lz4hc

Support pre-trained dictionary param.  Just like lz4, lz4hc doesn't
mandate specific format of the dictionary and zstd --train can be used to
train a dictionary for lz4, according to [1].

TEST
====

*** lz4hc
/sys/block/zram0/mm_stat
1750638592 608954620 621031424        0 621031424        1        0    34288    34288

*** lz4hc dict=/etc/lz4-dict-amd64
/sys/block/zram0/mm_stat
1750671360 505068582 514994176        0 514994176        1        0    34278    34278

[1] https://github.com/lz4/lz4/issues/557

Link: https://lkml.kernel.org/r/20240902105656.1383858-22-senozhatsky@chromium.orgSigned-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nick Terrell <terrelln@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/backend_lz4hc.c

@@ -5,6 +5,13 @@
 
 #include "backend_lz4hc.h"
 
+struct lz4hc_ctx {
+	void *mem;
+
+	LZ4_streamDecode_t *dstrm;
+	LZ4_streamHC_t *cstrm;
+};
+
 static void lz4hc_release_params(struct zcomp_params *params)
 {
 }
@@ -19,25 +26,67 @@ static int lz4hc_setup_params(struct zcomp_params *params)
 
 static void lz4hc_destroy(struct zcomp_ctx *ctx)
 {
-	vfree(ctx->context);
+	struct lz4hc_ctx *zctx = ctx->context;
+
+	if (!zctx)
+		return;
+
+	kfree(zctx->dstrm);
+	kfree(zctx->cstrm);
+	vfree(zctx->mem);
+	kfree(zctx);
 }
 
 static int lz4hc_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
 {
-	ctx->context = vmalloc(LZ4HC_MEM_COMPRESS);
-	if (!ctx->context)
+	struct lz4hc_ctx *zctx;
+
+	zctx = kzalloc(sizeof(*zctx), GFP_KERNEL);
+	if (!zctx)
 		return -ENOMEM;
 
+	ctx->context = zctx;
+	if (params->dict_sz == 0) {
+		zctx->mem = vmalloc(LZ4HC_MEM_COMPRESS);
+		if (!zctx->mem)
+			goto error;
+	} else {
+		zctx->dstrm = kzalloc(sizeof(*zctx->dstrm), GFP_KERNEL);
+		if (!zctx->dstrm)
+			goto error;
+
+		zctx->cstrm = kzalloc(sizeof(*zctx->cstrm), GFP_KERNEL);
+		if (!zctx->cstrm)
+			goto error;
+	}
+
 	return 0;
+
+error:
+	lz4hc_destroy(ctx);
+	return -EINVAL;
 }
 
 static int lz4hc_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
 			  struct zcomp_req *req)
 {
+	struct lz4hc_ctx *zctx = ctx->context;
 	int ret;
 
-	ret = LZ4_compress_HC(req->src, req->dst, req->src_len, req->dst_len,
-			      params->level, ctx->context);
+	if (!zctx->cstrm) {
+		ret = LZ4_compress_HC(req->src, req->dst, req->src_len,
+				      req->dst_len, params->level,
+				      zctx->mem);
+	} else {
+		/* Cstrm needs to be reset */
+		LZ4_resetStreamHC(zctx->cstrm, params->level);
+		ret = LZ4_loadDictHC(zctx->cstrm, params->dict,
+				     params->dict_sz);
+		if (ret != params->dict_sz)
+			return -EINVAL;
+		ret = LZ4_compress_HC_continue(zctx->cstrm, req->src, req->dst,
+					       req->src_len, req->dst_len);
+	}
 	if (!ret)
 		return -EINVAL;
 	req->dst_len = ret;
@@ -47,10 +96,22 @@ static int lz4hc_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
 static int lz4hc_decompress(struct zcomp_params *params, struct zcomp_ctx *ctx,
 			    struct zcomp_req *req)
 {
+	struct lz4hc_ctx *zctx = ctx->context;
 	int ret;
 
-	ret = LZ4_decompress_safe(req->src, req->dst, req->src_len,
-				  req->dst_len);
+	if (!zctx->dstrm) {
+		ret = LZ4_decompress_safe(req->src, req->dst, req->src_len,
+					  req->dst_len);
+	} else {
+		/* Dstrm needs to be reset */
+		ret = LZ4_setStreamDecode(zctx->dstrm, params->dict,
+					  params->dict_sz);
+		if (!ret)
+			return -EINVAL;
+		ret = LZ4_decompress_safe_continue(zctx->dstrm, req->src,
+						   req->dst, req->src_len,
+						   req->dst_len);
+	}
 	if (ret < 0)
 		return -EINVAL;
 	return 0;