memfd-util: add wrapper for memfd_create

The wrapper removes the flags MFD_EXEC and MFD_NOEXEC_SEAL when running
on kernels not understanding those flags.

src/basic/memfd-util.c

@@ -20,6 +20,22 @@
 #include "string-util.h"
 #include "utf8.h"
 
+int memfd_create_wrapper(const char *name, unsigned mode) {
+        unsigned mode_compat;
+        int mfd;
+
+        mfd = RET_NERRNO(memfd_create(name, mode));
+        if (mfd != -EINVAL)
+                return mfd;
+
+        mode_compat = mode & ~(MFD_EXEC | MFD_NOEXEC_SEAL);
+
+        if (mode == mode_compat)
+                return mfd;
+
+        return RET_NERRNO(memfd_create(name, mode_compat));
+}
+
 int memfd_new(const char *name) {
         _cleanup_free_ char *g = NULL;
 

src/basic/memfd-util.h

@@ -6,6 +6,8 @@
 #include <stdint.h>
 #include <sys/types.h>
 
+int memfd_create_wrapper(const char *name, unsigned mode);
+
 int memfd_new(const char *name);
 int memfd_new_and_map(const char *name, size_t sz, void **p);
 int memfd_new_and_seal(const char *name, const void *data, size_t sz);