[PATCH v3] blkdiscard: new applet

[Ari Sundholm]

Hi!

Your changes to the patch look fine, apart from one detail. The reason
why the applet checks for block deviceness before open(2) is that the
behavior of open(2) with the O_EXCL flag, but without the O_CREAT flag,
is undefined unless the file is a block device. It is your call whether
this is a sufficient reason for increasing the code size a bit.

Best regards,
Ari Sundholm
ari at tuxera.com

On Sat, 2016-01-02 at 00:21 +0000, Denys Vlasenko wrote:
> Applied, thanks!
> 
> Please try and yell at me if something's not right.
> 
> On Tue, Dec 1, 2015 at 2:55 PM, Ari Sundholm <ari at tuxera.com> wrote:
> > 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
> >
> >
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