feat(fcntl): fcntl/open flag handling

src/fcntl/posix_fadvise.c

@@ -0,0 +1,24 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <fcntl.h>
+
+#include "../internal/syscall.h"
+
+/*
+ * posix_fadvise over SYS_fadvise64 (221). POSIX return convention, unlike
+ * the rest of the family: an error NUMBER directly — 0 on success, else
+ * the positive errno value (EBADF, ESPIPE, EINVAL, ...) — and errno is
+ * left untouched. The raw syscall result is therefore mapped without the
+ * syscall_ret() translation (which would write errno): a negative return
+ * is negated, 0 stays 0. On x86_64 the syscall takes the offset as one
+ * 64-bit value (fd, offset, len, advice) — no lo/hi split.
+ */
+int
+posix_fadvise(int fd, off_t offset, off_t len, int advice)
+{
+    long r = __syscall4(SYS_fadvise64, fd, offset, len, advice);
+
+    return r < 0 ? (int)-r : 0;
+}