Avoid symbol collision with in-kernel zstdlib

For Linux, when zfs is compiled as an in kernel static variant
and the in kernel zstd library is compiled statically into the kernel
a symbol collision will occur.  This wrapper header renames all
of the relevant zstd functions to avoid this problem.
Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Sebastian Gottschall <s.gottschall@dd-wrt.com>
Closes #10775 

include/sys/zstd/zstd.h

@@ -83,13 +83,13 @@ typedef struct zfs_zstd_header {
 int zstd_init(void);
 void zstd_fini(void);
 
-size_t zstd_compress(void *s_start, void *d_start, size_t s_len, size_t d_len,
-    int level);
-int zstd_get_level(void *s_start, size_t s_len, uint8_t *level);
-int zstd_decompress_level(void *s_start, void *d_start, size_t s_len,
+size_t zfs_zstd_compress(void *s_start, void *d_start, size_t s_len,
+    size_t d_len, int level);
+int zfs_zstd_get_level(void *s_start, size_t s_len, uint8_t *level);
+int zfs_zstd_decompress_level(void *s_start, void *d_start, size_t s_len,
     size_t d_len, uint8_t *level);
-int zstd_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len,
-    int n);
+int zfs_zstd_decompress(void *s_start, void *d_start, size_t s_len,
+    size_t d_len, int n);
 
 #ifdef	__cplusplus
 }

lib/libzstd/Makefile.am

@@ -13,3 +13,9 @@ KERNEL_C = \
 	zfs_zstd.c
 
 nodist_libzstd_la_SOURCES = $(KERNEL_C)
+
+lib/zstd.$(OBJEXT):  CFLAGS += -fno-tree-vectorize -include $(top_srcdir)/module/zstd/include/zstd_compat_wrapper.h -Wp,-w
+lib/zstd.l$(OBJEXT): CFLAGS += -fno-tree-vectorize -include $(top_srcdir)/module/zstd/include/zstd_compat_wrapper.h -Wp,-w
+
+zfs_zstd.$(OBJEXT):  CFLAGS += -include $(top_srcdir)/module/zstd/include/zstd_compat_wrapper.h
+zfs_zstd.l$(OBJEXT): CFLAGS += -include $(top_srcdir)/module/zstd/include/zstd_compat_wrapper.h

module/zfs/zio_compress.c

@@ -66,8 +66,8 @@ zio_compress_info_t zio_compress_table[ZIO_COMPRESS_FUNCTIONS] = {
 	{"gzip-9",	9,	gzip_compress,	gzip_decompress, NULL},
 	{"zle",		64,	zle_compress,	zle_decompress, NULL},
 	{"lz4",		0,	lz4_compress_zfs, lz4_decompress_zfs, NULL},
-	{"zstd",	ZIO_ZSTD_LEVEL_DEFAULT,	zstd_compress, zstd_decompress,
-	    zstd_decompress_level},
+	{"zstd",	ZIO_ZSTD_LEVEL_DEFAULT,	zfs_zstd_compress,
+	    zfs_zstd_decompress, zfs_zstd_decompress_level},
 };
 
 uint8_t

module/zstd/Makefile.in

@@ -24,7 +24,9 @@ $(obj)/lib/zstd.o: c_flags += -fno-tree-vectorize
 $(obj)/lib/zstd.o: c_flags += -Wframe-larger-than=20480
 
 # Disable aarch64 neon SIMD instructions for kernel mode
-$(obj)/lib/zstd.o: c_flags += -include $(zstd_include)/aarch64_compat.h
+$(obj)/lib/zstd.o: c_flags += -include $(zstd_include)/aarch64_compat.h -include $(zstd_include)/zstd_compat_wrapper.h -Wp,-w
+
+$(obj)/zfs_zstd.o: c_flags += -include $(zstd_include)/zstd_compat_wrapper.h
 
 $(MODULE)-objs += zfs_zstd.o
 $(MODULE)-objs += lib/zstd.o

module/zstd/README.md

@@ -48,6 +48,11 @@ ${zstd}/contrib/single_file_libs/combine.sh \
     -r ${zstd}/lib -o module/zstd/lib/zstd.c module/zstd/zstd-in.c
 ~~~
 
+Note: if the zstd library for zfs is updated to a newer version,
+the macro list in include/zstd_compat_wrapper.h usually needs to be updated.
+this can be done with some hand crafting of the output of the following
+script: nm zstd.o | awk '{print "#define "$3 " zfs_" $3}' > macrotable
+
 
 ## Altering ZSTD and breaking changes
 

module/zstd/zfs_zstd.c

@@ -342,7 +342,7 @@ zstd_enum_to_level(enum zio_zstd_levels level, int16_t *zstd_level)
 
 /* Compress block using zstd */
 size_t
-zstd_compress(void *s_start, void *d_start, size_t s_len, size_t d_len,
+zfs_zstd_compress(void *s_start, void *d_start, size_t s_len, size_t d_len,
     int level)
 {
 	size_t c_len;
@@ -446,8 +446,8 @@ zstd_compress(void *s_start, void *d_start, size_t s_len, size_t d_len,
 
 /* Decompress block using zstd and return its stored level */
 int
-zstd_decompress_level(void *s_start, void *d_start, size_t s_len, size_t d_len,
-    uint8_t *level)
+zfs_zstd_decompress_level(void *s_start, void *d_start, size_t s_len,
+    size_t d_len, uint8_t *level)
 {
 	ZSTD_DCtx *dctx;
 	size_t result;
@@ -521,11 +521,12 @@ zstd_decompress_level(void *s_start, void *d_start, size_t s_len, size_t d_len,
 
 /* Decompress datablock using zstd */
 int
-zstd_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len,
+zfs_zstd_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len,
     int level __maybe_unused)
 {
 
-	return (zstd_decompress_level(s_start, d_start, s_len, d_len, NULL));
+	return (zfs_zstd_decompress_level(s_start, d_start, s_len, d_len,
+	    NULL));
 }
 
 /* Allocator for zstd compression context using mempool_allocator */
@@ -731,7 +732,7 @@ ZFS_MODULE_DESCRIPTION("ZSTD Compression for ZFS");
 ZFS_MODULE_LICENSE("BSD");
 ZFS_MODULE_VERSION(ZSTD_VERSION_STRING);
 
-EXPORT_SYMBOL(zstd_compress);
-EXPORT_SYMBOL(zstd_decompress_level);
-EXPORT_SYMBOL(zstd_decompress);
+EXPORT_SYMBOL(zfs_zstd_compress);
+EXPORT_SYMBOL(zfs_zstd_decompress_level);
+EXPORT_SYMBOL(zfs_zstd_decompress);
 #endif