libkmod/zstd: Allow to load libzstd.so on demand

Use dlfcn helpers to load libzstd once it's needed.

Signed-off-by: Lucas De Marchi <[email protected]>
Reviewed-by: Emil Velikov <[email protected]>
Link: #262

libkmod/libkmod-file-zstd.c

@@ -3,6 +3,9 @@
  * Copyright © 2024 Intel Corporation
  */
 
+/* TODO: replace with build system define once supported */
+#define DLSYM_LOCALLY_ENABLED 0
+
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -19,6 +22,24 @@
 #include "libkmod-internal.h"
 #include "libkmod-internal-file.h"
 
+#define DL_SYMBOL_TABLE(M)          \
+	M(ZSTD_decompress)          \
+	M(ZSTD_getErrorName)        \
+	M(ZSTD_getFrameContentSize) \
+	M(ZSTD_isError)
+
+DL_SYMBOL_TABLE(DECLARE_SYM)
+
+static int dlopen_zstd(void)
+{
+	static void *dl = NULL;
+
+	if (!DLSYM_LOCALLY_ENABLED)
+		return 0;
+
+	return dlsym_many(&dl, "libzstd.so.1", DL_SYMBOL_TABLE(DLSYM_ARG) NULL);
+}
+
 int kmod_file_load_zstd(struct kmod_file *file)
 {
 	void *src_buf = MAP_FAILED, *dst_buf = NULL;
@@ -27,6 +48,13 @@ int kmod_file_load_zstd(struct kmod_file *file)
 	struct stat st;
 	int ret;
 
+	ret = dlopen_zstd();
+	if (ret < 0) {
+		ERR(file->ctx, "zstd: can't load and resolve symbols (%s)",
+		    strerror(-ret));
+		return -EINVAL;
+	}
+
 	if (fstat(file->fd, &st) < 0) {
 		ret = -errno;
 		ERR(file->ctx, "zstd: %m\n");
@@ -45,7 +73,7 @@ int kmod_file_load_zstd(struct kmod_file *file)
 		goto out;
 	}
 
-	frame_size = ZSTD_getFrameContentSize(src_buf, src_size);
+	frame_size = sym_ZSTD_getFrameContentSize(src_buf, src_size);
 	if (frame_size == 0 || frame_size == ZSTD_CONTENTSIZE_UNKNOWN ||
 	    frame_size == ZSTD_CONTENTSIZE_ERROR) {
 		ret = -EINVAL;
@@ -65,9 +93,9 @@ int kmod_file_load_zstd(struct kmod_file *file)
 		goto out;
 	}
 
-	dst_size = ZSTD_decompress(dst_buf, dst_size, src_buf, src_size);
-	if (ZSTD_isError(dst_size)) {
-		ERR(file->ctx, "zstd: %s\n", ZSTD_getErrorName(dst_size));
+	dst_size = sym_ZSTD_decompress(dst_buf, dst_size, src_buf, src_size);
+	if (sym_ZSTD_isError(dst_size)) {
+		ERR(file->ctx, "zstd: %s\n", sym_ZSTD_getErrorName(dst_size));
 		ret = -EINVAL;
 		goto out;
 	}