libc: io: implement file io buffering and internal locking for concurrency

lib/libc/io/unistd/write.c

@@ -0,0 +1,21 @@
+#include <errno.h>
+#include <mango/handle.h>
+#include <mango/msg.h>
+#include <rosetta/fs.h>
+#include <sys/remote.h>
+
+int write(int fd, const void *buf, size_t count)
+{
+	int err;
+	size_t nr_written;
+	kern_status_t status = fs_write(fd, buf, count, &err, &nr_written);
+	if (status != KERN_OK) {
+		return __set_errno(__errno_from_kern_status(status));
+	}
+
+	if (err != SUCCESS) {
+		return __set_errno(err);
+	}
+
+	return nr_written;
+}