compress: introduce dlopen_compress() and friends

src/basic/compress.c

@@ -424,6 +424,32 @@ int dlopen_bzip2(int log_level) {
 #endif
 }
 
+int dlopen_compress_journal(Compression c, int log_level) {
+        switch (c) {
+        case COMPRESSION_NONE:
+                return 0;
+        case COMPRESSION_XZ:
+                return dlopen_xz(log_level);
+        case COMPRESSION_LZ4:
+                return dlopen_lz4(log_level);
+        case COMPRESSION_ZSTD:
+                return dlopen_zstd(log_level);
+        default:
+                return -EOPNOTSUPP;
+        }
+}
+
+int dlopen_compress(Compression c, int log_level) {
+        switch (c) {
+        case COMPRESSION_GZIP:
+                return dlopen_zlib(log_level);
+        case COMPRESSION_BZIP2:
+                return dlopen_bzip2(log_level);
+        default:
+                return dlopen_compress_journal(c, log_level);
+        }
+}
+
 static int compress_blob_xz(
                 const void *src,
                 uint64_t src_size,

src/basic/compress.h

@@ -102,6 +102,12 @@ int dlopen_zstd(int log_level) _dlopen_loader_;
 int dlopen_zlib(int log_level) _dlopen_loader_;
 int dlopen_bzip2(int log_level) _dlopen_loader_;
 
+int dlopen_compress(Compression c, int log_level);
+int dlopen_compress_journal(Compression c, int log_level);
+static inline int dlopen_compress_default(int log_level) {
+        return dlopen_compress_journal(DEFAULT_COMPRESSION, log_level);
+}
+
 static inline const char* default_compression_extension(void) {
         return compression_extension_to_string(DEFAULT_COMPRESSION) ?: "";
 }