[PATCH v3] blkdiscard: new applet

[Ari Sundholm]

From: Ari Sundholm <ari at tuxera.com>

This applet discards blocks on a given device.
Tested with multiple 32-bit and 64-bit kernel versions and two different SSDs.

function                                             old     new   delta
blkdiscard_main                                        -     300    +300
.rodata                                           154690  154795    +105
packed_usage                                       30275   30310     +35
applet_names                                        2499    2510     +11
applet_main                                         2904    2912      +8
applet_nameofs                                       726     728      +2
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 5/0 up/down: 461/0)             Total: 461 bytes

v2: Use a common error message format string when !S_ISBLK() to save space.
v3: Make the applet configuration option default to n and add a comment
    regarding two not strictly necessary variables which help readability.

Signed-off-by: Ari Sundholm <ari at tuxera.com>
---
 util-linux/blkdiscard.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 util-linux/blkdiscard.c

diff --git a/util-linux/blkdiscard.c b/util-linux/blkdiscard.c
new file mode 100644
index 0000000..0d28da2
--- /dev/null
+++ b/util-linux/blkdiscard.c
@@ -0,0 +1,86 @@
+/*
+ * Mini blkdiscard implementation for busybox
+ *
+ * Copyright (C) 2015 by Ari Sundholm <ari at tuxera.com> and Tuxera Inc.
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+
+//config:config BLKDISCARD
+//config:	bool "blkdiscard"
+//config:	default n
+//config:	help
+//config:	  blkdiscard discards sectors on a given device.
+
+//kbuild:lib-$(CONFIG_BLKDISCARD) += blkdiscard.o
+//applet:IF_BLKDISCARD(APPLET_NOFORK(blkdiscard, blkdiscard, BB_DIR_USR_BIN, BB_SUID_DROP, blkdiscard))
+
+//usage:#define blkdiscard_trivial_usage
+//usage:       "[-o offset] [-l length] [-s] device"
+//usage:#define blkdiscard_full_usage "\n\n"
+//usage:	"Discard sectors on the given device\n"
+//usage:	"\n	-o offset	Byte offset into device (default: 0)"
+//usage:	"\n	-l length	Number of bytes to discard (default: size of device)"
+//usage:	"\n	-s		Perform a secure discard"
+//usage:
+//usage:#define blkdiscard_example_usage
+//usage:	"$ blkdiscard -o 0 -l 1G /dev/sdb"
+
+#include "libbb.h"
+#include <linux/fs.h>
+
+/* This is a NOFORK applet. Be very careful! */
+
+int blkdiscard_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int blkdiscard_main(int argc UNUSED_PARAM, char **argv)
+{
+	unsigned opts;
+	char *offset_str;
+	char *length_str;
+	uint64_t offset = 0; /* Leaving these two variables out does not  */
+	uint64_t length;     /* shrink code size and hampers readability. */
+	uint64_t range[2];
+	struct stat st;
+	int fd;
+
+	enum {
+		OPT_OFFSET = (1 << 0),
+		OPT_LENGTH = (1 << 1),
+		OPT_SECURE = (1 << 2),
+	};
+
+	opt_complementary = "=1";
+	opts = getopt32(argv, "o:l:s", &offset_str, &length_str);
+
+	xstat(argv[optind], &st);
+	if (!S_ISBLK(st.st_mode))
+		bb_error_msg_and_die("%s: not a block device", argv[optind]);
+
+	fd = xopen(argv[optind], O_RDWR|O_EXCL);
+
+	if (opts & OPT_OFFSET)
+		offset = xatoull_sfx(offset_str, kMG_suffixes);
+
+	if (opts & OPT_LENGTH)
+		length = xatoull_sfx(length_str, kMG_suffixes);
+	else {
+		ioctl_or_perror_and_die(fd, BLKGETSIZE64, &length,
+			"Failed to get device size");
+		length -= offset;
+	}
+
+	range[0] = offset;
+	range[1] = length;
+	ioctl_or_perror_and_die(fd,
+				(opts & OPT_SECURE)
+				? BLKSECDISCARD
+				: BLKDISCARD, &range,
+				"%s failed",
+				(opts & OPT_SECURE)
+				? "BLKSECDISCARD"
+				: "BLKDISCARD");
+
+	xclose(fd);
+
+	return EXIT_SUCCESS;
+}
-- 
1.9.1