zram: add zstd compression backend support

Add s/w zstd compression.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Sergey Senozhatsky <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Nick Terrell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/block/zram/Kconfig

···
 	select LZ4HC_COMPRESS
 	select LZ4_DECOMPRESS
 
+config ZRAM_BACKEND_ZSTD
+	bool "zstd compression support"
+	depends on ZRAM
+	select ZSTD_COMPRESS
+	select ZSTD_DECOMPRESS
+
 choice
 	prompt "Default zram compressor"
 	default ZRAM_DEF_COMP_LZORLE
···
 	bool "lz4hc"
 	depends on ZRAM_BACKEND_LZ4HC
 
+config ZRAM_DEF_COMP_ZSTD
+	bool "zstd"
+	depends on ZRAM_BACKEND_ZSTD
+
 endchoice
 
 config ZRAM_DEF_COMP
···
 	default "lzo" if ZRAM_DEF_COMP_LZO
 	default "lz4" if ZRAM_DEF_COMP_LZ4
 	default "lz4hc" if ZRAM_DEF_COMP_LZ4HC
+	default "zstd" if ZRAM_DEF_COMP_ZSTD
 	default "unset-value"
 
 config ZRAM_WRITEBACK

drivers/block/zram/Makefile

···
 zram-$(CONFIG_ZRAM_BACKEND_LZO)		+= backend_lzorle.o backend_lzo.o
 zram-$(CONFIG_ZRAM_BACKEND_LZ4)		+= backend_lz4.o
 zram-$(CONFIG_ZRAM_BACKEND_LZ4HC)	+= backend_lz4hc.o
+zram-$(CONFIG_ZRAM_BACKEND_ZSTD)	+= backend_zstd.o
 
 obj-$(CONFIG_ZRAM)	+=	zram.o

drivers/block/zram/backend_zstd.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/zstd.h>
+
+#include "backend_zstd.h"
+
+struct zstd_ctx {
+	zstd_cctx *cctx;
+	zstd_dctx *dctx;
+	void *cctx_mem;
+	void *dctx_mem;
+	s32 level;
+};
+
+static void zstd_destroy(void *ctx)
+{
+	struct zstd_ctx *zctx = ctx;
+
+	vfree(zctx->cctx_mem);
+	vfree(zctx->dctx_mem);
+	kfree(zctx);
+}
+
+static void *zstd_create(void)
+{
+	zstd_parameters params;
+	struct zstd_ctx *ctx;
+	size_t sz;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return NULL;
+
+	ctx->level = zstd_default_clevel();
+	params = zstd_get_params(ctx->level, 0);
+	sz = zstd_cctx_workspace_bound(&params.cParams);
+	ctx->cctx_mem = vzalloc(sz);
+	if (!ctx->cctx_mem)
+		goto error;
+
+	ctx->cctx = zstd_init_cctx(ctx->cctx_mem, sz);
+	if (!ctx->cctx)
+		goto error;
+
+	sz = zstd_dctx_workspace_bound();
+	ctx->dctx_mem = vzalloc(sz);
+	if (!ctx->dctx_mem)
+		goto error;
+
+	ctx->dctx = zstd_init_dctx(ctx->dctx_mem, sz);
+	if (!ctx->dctx)
+		goto error;
+
+	return ctx;
+
+error:
+	zstd_destroy(ctx);
+	return NULL;
+}
+
+static int zstd_compress(void *ctx, const unsigned char *src, size_t src_len,
+			 unsigned char *dst, size_t *dst_len)
+{
+	struct zstd_ctx *zctx = ctx;
+	const zstd_parameters params = zstd_get_params(zctx->level, 0);
+	size_t ret;
+
+	ret = zstd_compress_cctx(zctx->cctx, dst, *dst_len,
+				 src, src_len, &params);
+	if (zstd_is_error(ret))
+		return -EINVAL;
+	*dst_len = ret;
+	return 0;
+}
+
+static int zstd_decompress(void *ctx, const unsigned char *src, size_t src_len,
+			   unsigned char *dst, size_t dst_len)
+{
+	struct zstd_ctx *zctx = ctx;
+	size_t ret;
+
+	ret = zstd_decompress_dctx(zctx->dctx, dst, dst_len, src, src_len);
+	if (zstd_is_error(ret))
+		return -EINVAL;
+	return 0;
+}
+
+const struct zcomp_ops backend_zstd = {
+	.compress	= zstd_compress,
+	.decompress	= zstd_decompress,
+	.create_ctx	= zstd_create,
+	.destroy_ctx	= zstd_destroy,
+	.name		= "zstd",
+};

drivers/block/zram/backend_zstd.h

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_ZSTD_H__
+#define __BACKEND_ZSTD_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_zstd;
+
+#endif /* __BACKEND_ZSTD_H__ */

drivers/block/zram/zcomp.c

···
 #include "backend_lzorle.h"
 #include "backend_lz4.h"
 #include "backend_lz4hc.h"
+#include "backend_zstd.h"
 
 static const struct zcomp_ops *backends[] = {
 #if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZO)
···
 #endif
 #if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZ4HC)
 	&backend_lz4hc,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_ZSTD)
+	&backend_zstd,
 #endif
 	NULL
 };