Re: [PATCH] xfs_io: add the lseek() SEEK_DATA/SEEK_HOLE support

Eric Sandeen
2013-08-20T23:07:35Z

On 8/16/13 3:54 PM, Mark Tinguely wrote:

> Add the lseek SEEK_DATA/SEEK_HOLE support into xfs_io.
> The result from the lseek() call will be printed to the output.
> For example:
>
> xfs_io> lseek -h 609k
> Type Offset
> hole 630784

HOLE not hole, I guess. ;)

I was going to say that's a lot of verbosity for a single output,
but I guess the other options might have many lines, so I suppose
it makes sense.

(I was just thinking about what xfstests might need to do to filter
& parse output...)

> Signed-off-by: Mark Tinguely <tinguely@sgi.com>
> ---
> Not trying to be difficult. Dave wanted the single hole/data/hole and data
> seperated from the recursive loop, but doing it that way is basically unrolling
> the loop into a if-then-else and is really terrible. If this is still not
> acceptable, then we can throw this feature into /dev/null.
>
> configure.ac | 1
> include/builddefs.in | 1
> io/Makefile | 5 +
> io/init.c | 1
> io/io.h | 6 +
> io/seek.c | 187 ++++++++++++++++++++++++++++++++++++++++++++++++++
> m4/package_libcdev.m4 | 15 ++++
> man/man8/xfs_io.8 | 35 +++++++++
> 8 files changed, 251 insertions(+)
>
> Index: b/configure.ac
> ===================================================================
> --- a/configure.ac
> +++ b/configure.ac
> @@ -110,6 +110,7 @@ AC_HAVE_GETMNTINFO
> AC_HAVE_FALLOCATE
> AC_HAVE_FIEMAP
> AC_HAVE_PREADV
> +AC_HAVE_SEEK_DATA
> AC_HAVE_SYNC_FILE_RANGE
> AC_HAVE_BLKID_TOPO($enable_blkid)
> AC_HAVE_READDIR
> Index: b/include/builddefs.in
> ===================================================================
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -102,6 +102,7 @@ HAVE_GETMNTINFO = @have_getmntinfo@
> HAVE_FALLOCATE = @have_fallocate@
> HAVE_FIEMAP = @have_fiemap@
> HAVE_PREADV = @have_preadv@
> +HAVE_SEEK_DATA = @have_seek_data@
> HAVE_SYNC_FILE_RANGE = @have_sync_file_range@
> HAVE_READDIR = @have_readdir@
>
> Index: b/io/Makefile
> ===================================================================
> --- a/io/Makefile
> +++ b/io/Makefile
> @@ -85,6 +85,11 @@ CFILES += readdir.c
> LCFLAGS += -DHAVE_READDIR
> endif
>
> +ifeq ($(HAVE_SEEK_DATA),yes)
> +LCFLAGS += -DHAVE_SEEK_DATA
> +CFILES += seek.c

see below; we should unconditionally compile, but conditionally
locally define SEEK_DATA / SEEK_HOLE

> +endif
> +
> default: depend $(LTCOMMAND)
>
> include $(BUILDRULES)
> Index: b/io/init.c
> ===================================================================
> --- a/io/init.c
> +++ b/io/init.c
> @@ -64,6 +64,7 @@ init_commands(void)
> help_init();
> imap_init();
> inject_init();
> + seek_init();
> madvise_init();
> mincore_init();
> mmap_init();
> Index: b/io/io.h
> ===================================================================
> --- a/io/io.h
> +++ b/io/io.h
> @@ -108,6 +108,12 @@ extern void quit_init(void);
> extern void shutdown_init(void);
> extern void truncate_init(void);
>
> +#ifdef HAVE_SEEK_DATA
> +extern void seek_init(void);
> +#else
> +#define seek_init() do { } while (0)
> +#endif

this can go when we unconditionally compile it in

> +
> #ifdef HAVE_FADVISE
> extern void fadvise_init(void);
> #else
> Index: b/io/seek.c
> ===================================================================
> --- /dev/null
> +++ b/io/seek.c
> @@ -0,0 +1,187 @@
> +/*
> + * Copyright (c) 2013 SGI
> + * All Rights Reserved.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it would be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write the Free Software Foundation,
> + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <libxfs.h>

hm, including this clashes w/ the min() define in io/init.h,
which is maybe a separate problem down the line, but libxfs.h
isn't required anyway for this file, so I'd just drop this include.

> +#include <linux/fs.h>
> +
> +#include <sys/uio.h>
> +#include <xfs/xfs.h>
> +#include <xfs/command.h>
> +#include <xfs/input.h>
> +#include <ctype.h>
> +#include "init.h"
> +#include "io.h"

#ifndef HAVE_SEEK_DATA
#define SEEK_DATA 3 /* seek to the next data */
#define SEEK_HOLE 4 /* seek to the next hole */
#endif

> +
> +static cmdinfo_t seek_cmd;
> +
> +static void
> +seek_help(void)
> +{
> + printf(_(
> +"\n"
> +" returns the next hole and/or data offset at or after the specified offset\n"
> +"\n"
> +" Example:\n"
> +" 'seek -d 512' - offset of data at or following offset 512\n"
> +" 'seek -a -r 0' - offsets of all data and hole in entire file\n"
> +"\n"
> +" Returns the offset of the next data and/or hole. There is an implied hole\n"
> +" at the end of file.

is this expected, given the hole at the end of the file? This is for a single
non-sparse file:

xfs_io> seek -ar 0
Type offset
DATA 0
HOLE 3022
DATA EOF

That last line doesn't make sense, does it?

> If the specified offset is past end of file, or there\n"
> +" is no data past the specied offset, EOF is returned.\n"

"specified"

> +" -a -- return the next data and hole starting at the specified offset.\n"
> +" -d -- return the next data starting at the specified offset.\n"
> +" -h -- return the next hole starting at the specified offset.\n"
> +" -r -- return all remaining type(s) starting at the specified offset.\n"
> +"\n"));
> +}
> +
> +#define SEEK_DFLAG (1 << 0)
> +#define SEEK_HFLAG (1 << 1)
> +#define SEEK_RFLAG (1 << 2)
> +#define DATA 0
> +#define HOLE 1
> +
> +struct seekinfo {
> + char *name;
> + int seektype;
> + int mask;
> +} seekinfo[] = {
> + {"DATA", SEEK_DATA, SEEK_DFLAG},
> + {"HOLE", SEEK_HOLE, SEEK_HFLAG}

I guess "DATA" doesn't get replaced by "0" ? Sorry, I failed cpp 101.
It prints the right thing so I guess not. ;)

> +};
> +
> +void
> +seek_output(
> + char *type,
> + off64_t offset)
> +{
> + if (offset == -1) {
> + if (errno == ENXIO)
> + printf("%s EOF\n", type);
> + else
> + printf("%s ERR %d\n", type, errno);
> + } else
> + printf("%s %ld\n", type, offset);
> +}
> +
> +static int
> +seek_f(
> + int argc,
> + char **argv)
> +{
> + off64_t offset, result;
> + size_t fsblocksize, fssectsize;
> + int flag;
> + int current; /* specify data or hole */
> + int c;
> +
> + flag = 0;
> + init_cvtnum(&fsblocksize, &fssectsize);
> +
> + while ((c = getopt(argc, argv, "adhr")) != EOF) {
> + switch (c) {
> + case 'a':
> + flag |= (SEEK_HFLAG | SEEK_DFLAG);
> + break;
> + case 'd':
> + flag |= SEEK_DFLAG;
> + break;
> + case 'h':
> + flag |= SEEK_HFLAG;
> + break;
> + case 'r':
> + flag |= SEEK_RFLAG;
> + break;
> + default:
> + return command_usage(&seek_cmd);
> + }
> + }
> + /* must have hole or data specified and an offset */
> + if (!(flag & (SEEK_DFLAG | SEEK_HFLAG)) ||
> + optind != argc - 1)
> + return command_usage(&seek_cmd);
> +
> + offset = cvtnum(fsblocksize, fssectsize, argv[optind]);

need to error check that:

xfs_io> seek -a 8x8
Type offset
HOLE EOF

> +
> + if (flag & SEEK_HFLAG) {
> + result = lseek64(file->fd, offset, SEEK_HOLE);
> + if ((result == offset) ||
> + !(flag & SEEK_DFLAG)) {
> + offset = result; /* in case it was EOF */
> + current = HOLE;
> + goto found_hole;
> + }

what if result < 0?

# io/xfs_io /tmp/fifo
xfs_io> seek -a 0
Type offset
DATA ERR 29

hum I guess seek_output handles it? perror would be nice, maybe?

> + }
> +
> + /* found data or -1 when "-a" option was requested */
> + current = DATA;
> + offset = lseek64(file->fd, offset, SEEK_DATA);

Ok, I guess I have to think harder about how the error handling
from lseek is supposed to work.

> +
> +found_hole:
> + printf("Type offset\n");
> +
> + while (flag) {
> + /*
> + * handle the data / hole entries in assending order from
> + * the specified offset.
> + *
> + * flag determines if there are more items to be displayed.
> + * SEEK_RFLAG is an infinite loop that is terminated with
> + * a offset at EOF.
> + *
> + * current determines next type to process/display where
> + * 0 is data and 1 is data.
> + */
> +
> + if (flag & seekinfo[current].mask) {
> + seek_output(seekinfo[current].name, offset);
> + if (offset == -1)
> + break; /* stop on error or EOF */
> + }
> +
> + /*
> + * When displaying only a single data and/or hole item, mask
> + * off the item as it is displayed. The loop will end when all
> + * requested items have been displayed.
> + */
> + if (!(flag & SEEK_RFLAG))
> + flag &= ~seekinfo[current].mask;
> +
> + current ^= 1; /* alternate between data and hole */
> + if (offset != -1)
> + offset = lseek64(file->fd, offset,
> + seekinfo[current].seektype);
> + }
> + return 0;
> +}
> +
> +void
> +seek_init(void)
> +{
> + seek_cmd.name = "seek";
> + seek_cmd.altname = "seek";

altname isn't required, but I don't think there's a reason to re-specify the same name.

> + seek_cmd.cfunc = seek_f;
> + seek_cmd.argmin = 2;
> + seek_cmd.argmax = 5;
> + seek_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
> + seek_cmd.args = _("-a | -d | -h [-r] off");
> + seek_cmd.oneline = _("locate the next data and/or hole");
> + seek_cmd.help = seek_help;
> +
> + add_command(&seek_cmd);
> +}
> Index: b/m4/package_libcdev.m4
> ===================================================================
> --- a/m4/package_libcdev.m4
> +++ b/m4/package_libcdev.m4
> @@ -154,6 +154,21 @@ AC_DEFUN([AC_HAVE_PREADV],
> ])
>
> #
> +# Check if we have a working fadvise system call

fadvise...? ;)

> +#
> +AC_DEFUN([AC_HAVE_SEEK_DATA],
> + [ AC_MSG_CHECKING([for seek_data ])

So really, we're checking for the SEEK_DATA & SEEK_HOLE defines here.

If they aren't present, we can locally define them, and we'll still get
the functionality (though io has to cope w/ EINVAL or whatnot if the
system xfs_io runs on doesn't understand the flags)

Also, coverity didn't find any errors in seek.c \o/ :)

Thanks,
-Eric

> + AC_TRY_COMPILE([
> +#include <linux/fs.h>
> + ], [
> + lseek(0, 0, SEEK_DATA);
> + ], have_seek_data=yes
> + AC_MSG_RESULT(yes),
> + AC_MSG_RESULT(no))
> + AC_SUBST(have_seek_data)
> + ])
> +
> +#
> # Check if we have a sync_file_range libc call (Linux)
> #
> AC_DEFUN([AC_HAVE_SYNC_FILE_RANGE],
> Index: b/man/man8/xfs_io.8
> ===================================================================
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -418,6 +418,41 @@ to read (in bytes)
> .RE
> .PD
> .TP
> +.TP
> +.BI "seek \-a | \-d | \-h [ \-r ] offset"
> +On platforms that support the
> +.BR lseek (2)
> +.B SEEK_DATA
> +and
> +.B SEEK_HOLE
> +options, display the offsets of the specified segments.
> +.RS 1.0i
> +.PD 0
> +.TP 0.4i
> +.B \-a
> +Display both
> +.B data
> +and
> +.B hole
> +segments starting at the specified
> +.B offset.
> +.TP
> +.B \-d
> +Display the
> +.B data
> +segment starting at the specified
> +.B offset.
> +.TP
> +.B \-h
> +Display the
> +.B hole
> +segment starting at the specified
> +.B offset.
> +.TP
> +.B \-r
> +Recursively display all the specified segments starting at the specified
> +.B offset.
> +.TP
>
> .SH MEMORY MAPPED I/O COMMANDS
> .TP
>
>
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