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Re: [PATCH 03/13] xfs_db: add crc manipulation commands

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH 03/13] xfs_db: add crc manipulation commands
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Thu, 19 Mar 2015 11:07:55 -0400
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1426624395-8258-4-git-send-email-sandeen@xxxxxxxxxx>
References: <1426624395-8258-1-git-send-email-sandeen@xxxxxxxxxx> <1426624395-8258-4-git-send-email-sandeen@xxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Tue, Mar 17, 2015 at 03:33:05PM -0500, Eric Sandeen wrote:
> This adds a new "crc" command to xfs_db for CRC-enabled filesystems.
> 
> If a structure has a CRC field, we can validate it, invalidate/corrupt
> it, or revalidate/rewrite it:
> 
> xfs_db> sb 0
> xfs_db> crc -v
> crc = 0x796c814f (correct)
> xfs_db> crc -i
> Metadata CRC error detected at block 0x0/0x200
> crc = 0x796c8150 (bad)
> xfs_db> crc -r
> crc = 0x796c814f (correct)
> 
> (-i and -r require "expert" write-capable mode)
> 
> This requires temporarily replacing the write verifier with
> a dummy which won't recalculate the CRC on the way to disk.
> 
> It also required me to write a new flist function, which is
> totally foreign to me, so hopefully done right - but it seems
> to work here.
> 
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
>  db/Makefile       |    2 +-
>  db/command.c      |    2 +
>  db/crc.c          |  188 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  db/crc.h          |   22 ++++++
>  db/flist.c        |   34 ++++++++++
>  db/flist.h        |    1 +
>  db/io.c           |   24 ++++++-
>  db/write.h        |    2 +-
>  man/man8/xfs_db.8 |   27 ++++++--
>  9 files changed, 293 insertions(+), 9 deletions(-)
>  create mode 100644 db/crc.c
>  create mode 100644 db/crc.h
> 
> diff --git a/db/Makefile b/db/Makefile
> index fb01bdd..500f94b 100644
> --- a/db/Makefile
> +++ b/db/Makefile
> @@ -8,7 +8,7 @@ include $(TOPDIR)/include/builddefs
>  LTCOMMAND = xfs_db
>  
>  HFILES = addr.h agf.h agfl.h agi.h attr.h attrshort.h bit.h block.h bmap.h \
> -     btblock.h bmroot.h check.h command.h convert.h debug.h \
> +     btblock.h bmroot.h check.h command.h convert.h crc.h debug.h \
>       dir2.h dir2sf.h dquot.h echo.h faddr.h field.h \
>       flist.h fprint.h frag.h freesp.h hash.h help.h init.h inode.h input.h \
>       io.h malloc.h metadump.h output.h print.h quit.h sb.h sig.h strvec.h \
> diff --git a/db/command.c b/db/command.c
> index b7e3165..d44e0a5 100644
> --- a/db/command.c
> +++ b/db/command.c
> @@ -48,6 +48,7 @@
>  #include "write.h"
>  #include "malloc.h"
>  #include "dquot.h"
> +#include "crc.h"
>  
>  cmdinfo_t    *cmdtab;
>  int          ncmds;
> @@ -123,6 +124,7 @@ init_commands(void)
>       bmap_init();
>       check_init();
>       convert_init();
> +     crc_init();
>       debug_init();
>       echo_init();
>       frag_init();
> diff --git a/db/crc.c b/db/crc.c
> new file mode 100644
> index 0000000..b58a594
> --- /dev/null
> +++ b/db/crc.c
> @@ -0,0 +1,188 @@
> +/*
> + * Copyright (c) 2014 Red Hat, Inc.
> + * 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 <xfs/libxfs.h>
> +#include "addr.h"
> +#include "command.h"
> +#include "type.h"
> +#include "faddr.h"
> +#include "fprint.h"
> +#include "field.h"
> +#include "flist.h"
> +#include "io.h"
> +#include "init.h"
> +#include "output.h"
> +#include "bit.h"
> +#include "print.h"
> +
> +static int crc_f(int argc, char **argv);
> +static void crc_help(void);
> +
> +static const cmdinfo_t crc_cmd =
> +     { "crc", NULL, crc_f, 0, 1, 0, "[-i|-r|-v]",
> +       N_("manipulate crc values for V5 filesystem structures"), crc_help };
> +
> +void
> +crc_init(void)
> +{
> +     if (xfs_sb_version_hascrc(&mp->m_sb))
> +             add_command(&crc_cmd);
> +}
> +
> +static void
> +crc_help(void)
> +{
> +     dbprintf(_(
> +"\n"
> +" 'crc' validates, invalidates, or recalculates the crc value for\n"
> +" the current on-disk metadata structures in Version 5 filesystems.\n"
> +"\n"
> +" Usage:  \"crc [-i|-r|-v]\"\n"
> +"\n"
> +));
> +
> +}
> +
> +static int
> +crc_f(
> +     int             argc,
> +     char            **argv)
> +{
> +     struct xfs_buf_ops nowrite_ops;
> +     const struct xfs_buf_ops *stashed_ops = NULL;
> +     extern char     *progname;
> +     const field_t   *fields;
> +     const ftattr_t  *fa;
> +     flist_t         *fl;
> +     int             invalidate = 0;
> +     int             recalculate = 0;
> +     int             validate = 0;
> +     int             c;
> +
> +     if (cur_typ == NULL) {
> +             dbprintf(_("no current type\n"));
> +             return 0;
> +     }
> +
> +     if (cur_typ->fields == NULL) {
> +             dbprintf(_("current type (%s) is not a structure\n"),
> +                      cur_typ->name);
> +             return 0;
> +     }
> +
> +     if (argc) while ((c = getopt(argc, argv, "irv")) != EOF) {

The 'if (argc)' thing strikes again. Does this address something I'm not
aware of?

> +             switch (c) {
> +             case 'i':
> +                     invalidate = 1;
> +                     break;
> +             case 'r':
> +                     recalculate = 1;
> +                     break;
> +             case 'v':
> +                     validate = 1;
> +                     break;
> +             default:
> +                     dbprintf(_("bad option for crc command\n"));
> +                     return 0;
> +             }
> +     } else
> +             validate = 1;
> +
> +     if (invalidate + recalculate + validate > 1) {
> +             dbprintf(_("crc command accepts only one option\n"));
> +             return 0;
> +     }
> +
> +     if ((invalidate || recalculate) &&
> +         ((x.isreadonly & LIBXFS_ISREADONLY) || !expert_mode)) {
> +             dbprintf(_("%s not in expert mode, writing disabled\n"),
> +                     progname);
> +             return 0;
> +     }
> +
> +     fields = cur_typ->fields;
> +
> +     /* if we're a root field type, go down 1 layer to get field list */
> +     if (fields->name[0] == '\0') {
> +             fa = &ftattrtab[fields->ftyp];
> +             ASSERT(fa->ftyp == fields->ftyp);
> +             fields = fa->subfld;
> +     }
> +
> +     /* Search for a CRC field */
> +     fl = flist_find_ftyp(fields, FLDT_CRC);
> +     if (!fl) {
> +             dbprintf(_("No CRC field found for type %s\n"), cur_typ->name);
> +             return 0;
> +     }
> +
> +     /* run down the field list and set offsets into the data */
> +     if (!flist_parse(fields, fl, iocur_top->data, 0)) {
> +             flist_free(fl);
> +             dbprintf(_("parsing error\n"));
> +             return 0;
> +     }
> +
> +     if (invalidate) {
> +             flist_t         *sfl;
> +             int             bit_length;
> +             int             parentoffset;
> +             int             crc;
> +
> +             sfl = fl;
> +             parentoffset = 0;
> +             while (sfl->child) {
> +                     parentoffset = sfl->offset;
> +                     sfl = sfl->child;
> +             }
> +             ASSERT(sfl->fld->ftyp == FLDT_CRC);
> +
> +             bit_length = fsize(sfl->fld, iocur_top->data, parentoffset, 0);
> +             bit_length *= fcount(sfl->fld, iocur_top->data, parentoffset);
> +             crc = getbitval(iocur_top->data, sfl->offset, bit_length, 
> BVUNSIGNED);
> +             /* Off by one.. */
> +             crc = cpu_to_be32(crc + 1);
> +             setbitval(iocur_top->data, sfl->offset, bit_length, &crc);

Some comments on the above code would be nice to explain what it's
calculating.

> +
> +             /* Temporarily remove write verifier to write a bad CRC */
> +             stashed_ops = iocur_top->bp->b_ops;
> +             nowrite_ops.verify_read = stashed_ops->verify_read;
> +             nowrite_ops.verify_write = xfs_dummy_verify;
> +             iocur_top->bp->b_ops = &nowrite_ops;
> +     }
> +
> +     if (invalidate || recalculate) {
> +             if (invalidate)
> +                     dbprintf(_("Invalidating CRC:\n"));
> +             else
> +                     dbprintf(_("Recalculating CRC:\n"));
> +
> +             write_cur();
> +             if (stashed_ops)
> +                     iocur_top->bp->b_ops = stashed_ops;
> +             /* re-verify to get proper b_error state */
> +             iocur_top->bp->b_ops->verify_read(iocur_top->bp);
> +     } else
> +             dbprintf(_("Verifying CRC:\n"));

Does the "verify" aspect of this command do anything, or are we just
printing the state that was determined from a previous cursor load? If
the latter, I wonder if it's worth retaining that option (e.g., just
print an inode to see the crc state)..?

> +
> +     /* And show us what we've got! */
> +     flist_print(fl);
> +     print_flist(fl);
> +     flist_free(fl);
> +     return 0;
> +}
> diff --git a/db/crc.h b/db/crc.h
> new file mode 100644
> index 0000000..9f44615
> --- /dev/null
> +++ b/db/crc.h
> @@ -0,0 +1,22 @@
> +/*
> + * Copyright (c) 2014 Red Hat, Inc.
> + * 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
> + */
> +
> +struct field;
> +
> +extern void  crc_init(void);
> +extern void  crc_struct(const field_t *fields, int argc, char **argv);
> diff --git a/db/flist.c b/db/flist.c
> index 33f7da7..fa19f70 100644
> --- a/db/flist.c
> +++ b/db/flist.c
> @@ -411,6 +411,40 @@ flist_split(
>       return v;
>  }
>  
> +/*
> + * Given a set of fields, scan for a field of the given type.
> + * Return an flist leading to the first found field
> + * of that type.
> + * Return NULL if no field of the given type is found.
> + */
> +flist_t *
> +flist_find_ftyp(
> +     const field_t *fields,
> +     fldt_t  type)
> +{
> +     flist_t *fl;
> +     const field_t   *f;
> +     const ftattr_t  *fa;
> +
> +     for (f = fields; f->name; f++) {
> +             fl = flist_make(f->name);
> +             fl->fld = f;
> +             if (f->ftyp == type)
> +                     return fl;
> +             fa = &ftattrtab[f->ftyp];
> +             if (fa->subfld) {
> +                     flist_t *nfl;
> +                     nfl = flist_find_ftyp(fa->subfld, type);
> +                     if (nfl) {
> +                             fl->child = nfl;
> +                             return fl;
> +                     }
> +             }
> +             flist_free(fl);

Ok, I haven't really dug into the type code to grok this, but it looks
like we're doing an flist allocation/free for each iteration of the
loop. Could we turn that inside out to only do that in the path where we
find the type to return? It looks to me like we could, but I could
easily be missing something.

> +     }
> +     return NULL;
> +}
> +
>  static void
>  ftok_free(
>       ftok_t  *ft)
> diff --git a/db/flist.h b/db/flist.h
> index 5c9fba0..3f4b312 100644
> --- a/db/flist.h
> +++ b/db/flist.h
> @@ -37,3 +37,4 @@ extern int  flist_parse(const struct field *fields, flist_t 
> *fl, void *obj,
>                           int startoff);
>  extern void  flist_print(flist_t *fl);
>  extern flist_t       *flist_scan(char *name);
> +extern flist_t       *flist_find_ftyp(const field_t *fields, fldt_t  type);
> diff --git a/db/io.c b/db/io.c
> index 91858e2..732b320 100644
> --- a/db/io.c
> +++ b/db/io.c
> @@ -27,6 +27,7 @@
>  #include "output.h"
>  #include "init.h"
>  #include "malloc.h"
> +#include "crc.h"
>  
>  static int   pop_f(int argc, char **argv);
>  static void     pop_help(void);
> @@ -466,22 +467,41 @@ xfs_dummy_verify(
>  void
>  write_cur(void)
>  {
> +     int skip_crc = 0;
> +
> +     if (iocur_top->bp->b_ops &&
> +         iocur_top->bp->b_ops->verify_write == xfs_dummy_verify)
> +             skip_crc = 1;
> +
>       if (iocur_sp < 0) {
>               dbprintf(_("nothing to write\n"));
>               return;
>       }
>  
> -     if (iocur_top->ino_buf) {
> +     if (iocur_top->ino_buf && !skip_crc) {
>               libxfs_dinode_calc_crc(mp, iocur_top->data);
>               iocur_top->ino_crc_ok = 1;
>       }
> -     if (iocur_top->dquot_buf)
> +
> +     if (iocur_top->dquot_buf && !skip_crc)
>               xfs_update_cksum(iocur_top->data, sizeof(struct xfs_dqblk),
>                                XFS_DQUOT_CRC_OFF);
>       if (iocur_top->bbmap)
>               write_cur_bbs();
>       else
>               write_cur_buf();
> +
> +     /* If we didn't write the crc automatically, re-check validity */
> +     if (iocur_top->ino_buf && skip_crc) {
> +             xfs_dinode_t    *dip;
> +             xfs_ino_t       ino;
> +
> +             dip = iocur_top->data;
> +             ino = iocur_top->ino;

ino is unused.

> +             iocur_top->ino_crc_ok = xfs_verify_cksum((char *)dip,
> +                                             mp->m_sb.sb_inodesize,
> +                                             XFS_DINODE_CRC_OFF);
> +     } 

Trailing space on the above line.

Brian

>  }
>  
>  void
> diff --git a/db/write.h b/db/write.h
> index 31e2665..664ddcc 100644
> --- a/db/write.h
> +++ b/db/write.h
> @@ -20,5 +20,5 @@ struct field;
>  
>  extern void  write_init(void);
>  extern void  write_block(const field_t *fields, int argc, char **argv);
> -extern void  write_string(const field_t *fields, int argc, char **argv);
>  extern void  write_struct(const field_t *fields, int argc, char **argv);
> +extern void  write_string(const field_t *fields, int argc, char **argv);
> diff --git a/man/man8/xfs_db.8 b/man/man8/xfs_db.8
> index d527230..46a1f39 100644
> --- a/man/man8/xfs_db.8
> +++ b/man/man8/xfs_db.8
> @@ -87,16 +87,14 @@ or
>  .I filename
>  read-only. This option is required if the filesystem is mounted.
>  It is only necessary to omit this flag if a command that changes data
> -.RB ( write ", " blocktrash )
> +.RB ( write ", " blocktrash ", " crc )
>  is to be used.
>  .TP
>  .B \-x
>  Specifies expert mode.
>  This enables the
> -.B write
> -and
> -.B blocktrash
> -commands.
> +.RB ( write ", " blocktrash ", " crc
> +invalidate/revalidate) commands.
>  .TP
>  .B \-V
>  Prints the version number and exits.
> @@ -409,6 +407,25 @@ conversions such as
>  .I agb
>  .BR fsblock .
>  .TP
> +.B crc [\-i|\-r|\-v]
> +Invalidates, revalidates, or validates the CRC (checksum)
> +field of the current structure, if it has one.
> +This command is available only on CRC-enabled filesystems.
> +With no argument, validation is performed.
> +Each command will display the resulting CRC value and state.
> +.RS 1.0i
> +.TP 0.4i
> +.B \-i
> +Invalidate the structure's CRC value (incrementing it by one),
> +and write it to disk.
> +.TP
> +.B \-r
> +Recalculate the current structure's correct CRC value, and write it to disk.
> +.TP
> +.B \-v
> +Validate and display the current value and state of the structure's CRC.
> +.RE
> +.TP
>  .BI "daddr [" d ]
>  Set current address to the daddr (512 byte block) given by
>  .IR d .
> -- 
> 1.7.1
> 
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