mkXXXX: unify [KBYTES] parameter handling (added it to mkswap)

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/get_volsize.c

@@ -0,0 +1,48 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2010 Denys Vlasenko
+ *
+ * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ */
+#include "libbb.h"
+
+uoff_t FAST_FUNC get_volume_size_in_bytes(int fd,
+		const char *override,
+		unsigned override_units,
+		int extend)
+{
+	uoff_t result;
+
+	if (override) {
+		result = XATOOFF(override);
+		if (result >= (uoff_t)(MAXINT(off_t)) / override_units)
+			bb_error_msg_and_die("image size is too big");
+		result *= override_units;
+		/* seek past end fails on block devices but works on files */
+		if (lseek(fd, result - 1, SEEK_SET) != (off_t)-1) {
+			if (extend)
+				xwrite(fd, "", 1); /* file grows if needed */
+		}
+		//else {
+		//	bb_error_msg("warning, block device is smaller");
+		//}
+	} else {
+		/* more portable than BLKGETSIZE[64] */
+		result = xlseek(fd, 0, SEEK_END);
+	}
+
+	xlseek(fd, 0, SEEK_SET);
+
+	/* Prevent things like this:
+	 * $ dd if=/dev/zero of=foo count=1 bs=1024
+	 * $ mkswap foo
+	 * Setting up swapspace version 1, size = 18446744073709548544 bytes
+	 *
+	 * Picked 16k arbitrarily: */
+	if (result < 16*1024)
+		bb_error_msg_and_die("image is too small");
+
+	return result;
+}