shred: new applet

function                                             old     new   delta
shred_main                                             -     361    +361
packed_usage                                       31427   31467     +40
applet_names                                        2578    2584      +6
applet_main                                         1492    1496      +4
run_applet_and_exit                                  679     682      +3
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 4/0 up/down: 414/0)             Total: 414 bytes

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

coreutils/cksum.c

@@ -17,9 +17,9 @@
 //kbuild:lib-$(CONFIG_CKSUM) += cksum.o
 
 //usage:#define cksum_trivial_usage
-//usage:       "FILES..."
+//usage:       "FILE..."
 //usage:#define cksum_full_usage "\n\n"
-//usage:       "Calculate the CRC32 checksums of FILES"
+//usage:       "Calculate the CRC32 checksums of FILEs"
 
 #include "libbb.h"
 #include "common_bufsiz.h"

coreutils/shred.c

@@ -0,0 +1,104 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//config:config SHRED
+//config:	bool "shred"
+//config:	default y
+//config:	help
+//config:	  Overwrite a file to hide its contents, and optionally delete it
+
+//applet:IF_SHRED(APPLET(shred, BB_DIR_USR_BIN, BB_SUID_DROP))
+
+//kbuild:lib-$(CONFIG_SHRED) += shred.o
+
+//usage:#define shred_trivial_usage
+//usage:       "FILE..."
+//usage:#define shred_full_usage "\n\n"
+//usage:       "Overwrite/delete FILEs\n"
+//usage:     "\n	-f	Chmod to ensure writability"
+//usage:     "\n	-n N	Overwrite N times (default 3)"
+//usage:     "\n	-z	Final overwrite with zeros"
+//usage:     "\n	-u	Remove file"
+//-x and -v are accepted but have no effect
+
+/* shred (GNU coreutils) 8.25:
+-f, --force		change permissions to allow writing if necessary
+-u			truncate and remove file after overwriting
+-z, --zero		add a final overwrite with zeros to hide shredding
+-n, --iterations=N	overwrite N times instead of the default (3)
+-v, --verbose		show progress
+-x, --exact		do not round file sizes up to the next full block; this is the default for non-regular files
+--random-source=FILE	get random bytes from FILE
+-s, --size=N		shred this many bytes (suffixes like K, M, G accepted)
+--remove[=HOW]		like -u but give control on HOW to delete;  See below
+*/
+
+#include "libbb.h"
+
+int shred_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int shred_main(int argc UNUSED_PARAM, char **argv)
+{
+	int rand_fd = rand_fd; /* for compiler */
+	int zero_fd;
+	unsigned num_iter = 3;
+	unsigned opt;
+	enum {
+		OPT_f = (1 << 0),
+		OPT_u = (1 << 1),
+		OPT_z = (1 << 2),
+		OPT_n = (1 << 3),
+		OPT_v = (1 << 4),
+		OPT_x = (1 << 5),
+	};
+
+	opt = getopt32(argv, "fuzn:+vx", &num_iter);
+	argv += optind;
+
+	zero_fd = xopen("/dev/zero", O_RDONLY);
+	if (num_iter != 0)
+		rand_fd = xopen("/dev/urandom", O_RDONLY);
+
+	if (!*argv)
+		bb_show_usage();
+
+	for (;;) {
+		struct stat sb;
+		unsigned i;
+		int fd = -1;
+
+		if (opt & OPT_f) {
+			fd = open(*argv, O_WRONLY);
+			if (fd < 0)
+				chmod(*argv, 0666);
+		}
+		if (fd < 0)
+			fd = xopen(*argv, O_WRONLY);
+
+		if (fstat(fd, &sb) == 0 && sb.st_size > 0) {
+			off_t size = sb.st_size;
+
+			for (i = 0; i < num_iter; i++) {
+				bb_copyfd_size(rand_fd, fd, size);
+				fdatasync(fd);
+				xlseek(fd, 0, SEEK_SET);
+			}
+			if (opt & OPT_z) {
+				bb_copyfd_size(zero_fd, fd, size);
+				fdatasync(fd);
+			}
+			if (opt & OPT_u) {
+				ftruncate(fd, 0);
+				xunlink(*argv);
+			}
+			xclose(fd);
+		}
+		argv++;
+		if (!*argv)
+			break;
+	}
+
+	return EXIT_SUCCESS;
+}