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List:       busybox
Subject:    Re: [PATCH v3] blkdiscard: new applet
From:       Ari Sundholm <ari () tuxera ! com>
Date:       2015-12-17 17:40:54
Message-ID: 1450374054.30943.6.camel () ari-lenovo
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Hi,

just a friendly ping. This applet is very useful for us working on
filesystem and block device related things on embedded platforms. It
implements a limited set of the operations available in the blkdiscard
in util-linux.

Best regards,
Ari Sundholm
ari@tuxera.com

On Tue, 2015-12-01 at 13:55 +0000, Ari Sundholm wrote:
> From: Ari Sundholm <ari@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@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@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;
> +}


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