Re: [PATCH 09/10] xfs_db: trash the block at the top of the cursor stack

Darrick J. Wong
2015-08-19T15:12:32Z

On Tue, Aug 18, 2015 at 02:59:28PM -0500, Eric Sandeen wrote:
> On 8/14/15 8:44 PM, Darrick J. Wong wrote:
> > Add a new -z option to blocktrash to make it trash the block that's at
> > the top of the stack, so that we can perform targeted fuzzing. While
> > we're at it, prevent fuzzing off the end of the buffer and add a -o
> > parameter so that we can specify an offset to start fuzzing from.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > db/check.c | 81 +++++++++++++++++++++++++++++++++++++++++------------
> > man/man8/xfs_db.8 | 15 +++++++++-
> > 2 files changed, 77 insertions(+), 19 deletions(-)
> >
> >
> > diff --git a/db/check.c b/db/check.c
> > index 965d0f5..7c11b0b 100644
> > --- a/db/check.c
> > +++ b/db/check.c
> > @@ -930,8 +930,7 @@ typedef struct ltab {
> >
> > static void
> > blocktrash_b(
> > - xfs_agnumber_t agno,
> > - xfs_agblock_t agbno,
> > + int offset,
>
> a comment about "offset into what?" might be nice
>
> > dbm_t type,
> > ltab_t *ltabp,
> > int mode)
> > @@ -943,23 +942,36 @@ blocktrash_b(
> > int len;
> > int mask;
> > int newbit;
> > - int offset;
> > const struct xfs_buf_ops *stashed_ops;
> > static char *modestr[] = {
> > N_("zeroed"), N_("set"), N_("flipped"), N_("randomized")
> > };
> > + xfs_agnumber_t agno;
> > + xfs_agblock_t agbno;
> >
> > + agno = XFS_FSB_TO_AGNO(mp, XFS_DADDR_TO_FSB(mp, iocur_top->bb));
> > + agbno = XFS_FSB_TO_AGBNO(mp, XFS_DADDR_TO_FSB(mp, iocur_top->bb));
> > + if (iocur_top->len == 0) {
> > + dbprintf(_("zero-length block %u/%u buffer to trash??\n"),
> > + agno, agbno);
> > + return;
> > + }
> > len = (int)((random() % (ltabp->max - ltabp->min + 1)) + ltabp->min);
> > - offset = (int)(random() % (int)(mp->m_sb.sb_blocksize * NBBY));
> > + /*
> > + * offset >= 0: start fuzzing at this exact offset.
>
> "this exact bit offset"
>
> > + * offset < 0: pick an offset at least as high at -(offset + 1).
>
> "a bit offset ..."
>
> (units would be nice, in the comments. I had assumed bytes, even though you have NBBY)

Ok.

> Ow, my brain. ;)
>
> Your manpage says:
>
> > If the value is preceded by a '+', the
> > +trashing will start at a randomly chosen offset that is larger than the value
> > +supplied.
>
> which seems sane.
>
> If we supply +10,
>
> + if (relative)
> + offset = -offset - 1;
>
> so now offset = -10 - 1, and we get -11.
> Then:
>
> > + */
> > + if (offset < 0) {
> > + offset = -(offset + 1);
>
> now offset = -(-11 + 1) = -(-10) = 10. Okay... so 10 or higher.
>
> What's w/ the +/- 1?

It's to distinguish "start fuzzing at exactly zero" from "pick anywhere
(at least as high as bit offset zero) to start fuzzing".

>
> Why not just:
>
> if (relative)
> offset = -offset; /* i.e. -10 */
>
> ...
>
> if (offset < 0) {
> offset = -offset; /* i.e. 10 */
> offset = offset + (int)(random() % (int)((iocur_top->len - offset) * NBBY)); ...
>
>
> > + offset = offset + (int)(random() % (int)((iocur_top->len - offset) * NBBY));
> > + }
> > + if (offset + len >= iocur_top->len * NBBY)
> > + len = (iocur_top->len * NBBY) - offset;
> > newbit = 0;
> > - push_cur();
> > - set_cur(NULL,
> > - XFS_AGB_TO_DADDR(mp, agno, agbno), blkbb, DB_RING_IGN, NULL);
> > stashed_ops = iocur_top->bp->b_ops;
> > iocur_top->bp->b_ops = NULL;
> > if ((buf = iocur_top->data) == NULL) {
> > dbprintf(_("can't read block %u/%u for trashing\n"), agno, agbno);
> > - pop_cur();
> > return;
> > }
> > for (bitno = 0; bitno < len; bitno++) {
> > @@ -988,7 +1000,6 @@ blocktrash_b(
> > }
> > write_cur();
> > iocur_top->bp->b_ops = stashed_ops;
> > - pop_cur();
> > printf(_("blocktrash: %u/%u %s block %d bit%s starting %d:%d %s\n"),
> > agno, agbno, typename[type], len, len == 1 ? "" : "s",
> > offset / NBBY, offset % NBBY, modestr[mode]);
> > @@ -1019,11 +1030,9 @@ blocktrash_f(
> > uint seed;
> > int sopt;
> > int tmask;
> > + bool this_block = false;
> > + int offset = -1;
> >
> > - if (!dbmap) {
> > - dbprintf(_("must run blockget first\n"));
> > - return 0;
> > - }
> > optind = 0;
> > count = 1;
> > min = 1;
> > @@ -1050,7 +1059,7 @@ blocktrash_f(
> > (1 << DBM_RTSUM) |
> > (1 << DBM_SYMLINK) |
> > (1 << DBM_SB);
> > - while ((c = getopt(argc, argv, "0123n:s:t:x:y:")) != EOF) {
> > + while ((c = getopt(argc, argv, "0123n:o:s:t:x:y:z")) != EOF) {
> > switch (c) {
> > case '0':
> > mode = 0;
> > @@ -1071,6 +1080,21 @@ blocktrash_f(
> > return 0;
> > }
> > break;
> > + case 'o': {
> > + int relative = 0;
> > + if (optarg[0] == '+') {
> > + optarg++;
> > + relative = 1;
> > + }
> > + offset = (int)strtol(optarg, &p, 0);
> > + if (*p != '\0' || offset < 0) {
> > + dbprintf(_("bad blocktrash offset %s\n"), optarg);
> > + return 0;
> > + }
> > + if (relative)
> > + offset = -offset - 1;
> > + break;
> > + }
> > case 's':
> > seed = (uint)strtoul(optarg, &p, 0);
> > sopt = 1;
> > @@ -1102,11 +1126,22 @@ blocktrash_f(
> > return 0;
> > }
> > break;
> > + case 'z':
> > + this_block = true;
> > + break;
>
> is there any mnemonic for 'z'? Maybe 'c' for Current, or 'b' for (this one) Block?
>
> Not that big a deal, just wondering.

-z for "Corrupt 'zis block, pleaze". :)

I was hoping it is less confusing than "-t" for "select eligible block types"
and "-T" for "corrupt this exact block"?

>
> > default:
> > dbprintf(_("bad option for blocktrash command\n"));
> > return 0;
> > }
> > }
> > + if (!this_block && !dbmap) {
> > + dbprintf(_("must run blockget first\n"));
> > + return 0;
> > + }
> > + if (this_block && iocur_sp == 0) {
> > + dbprintf(_("nothing on stack\n"));
> > + return 0;
> > + }
> > if (min > max) {
> > dbprintf(_("bad min/max for blocktrash command\n"));
> > return 0;
> > @@ -1125,6 +1160,14 @@ blocktrash_f(
> > } else
> > lentab[lentablen - 1].max = i;
> > }
> > + if (!sopt)
> > + dbprintf(_("blocktrash: seed %u\n"), seed);
>
> does this extra output break any xfstests?
>
> # grep -r blocktrash common/ tests/xfs
> #
>
> maybe not!

<shrug> I made the same observation.

--D

>
> > + srandom(seed);
> > + if (this_block) {
> > + blocktrash_b(offset, DBM_UNKNOWN, &lentab[random() % lentablen],
> > + mode);
> > + goto out;
> > + }
> > for (blocks = 0, agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
> > for (agbno = 0, p = dbmap[agno];
> > agbno < mp->m_sb.sb_agblocks;
> > @@ -1137,9 +1180,6 @@ blocktrash_f(
> > dbprintf(_("blocktrash: no matching blocks\n"));
> > goto out;
> > }
> > - if (!sopt)
> > - dbprintf(_("blocktrash: seed %u\n"), seed);
> > - srandom(seed);
> > for (i = 0; i < count; i++) {
> > randb = (xfs_rfsblock_t)((((__int64_t)random() << 32) |
> > random()) % blocks);
> > @@ -1153,8 +1193,13 @@ blocktrash_f(
> > continue;
> > if (bi++ < randb)
> > continue;
> > - blocktrash_b(agno, agbno, (dbm_t)*p,
> > + push_cur();
> > + set_cur(NULL,
> > + XFS_AGB_TO_DADDR(mp, agno, agbno),
> > + blkbb, DB_RING_IGN, NULL);
> > + blocktrash_b(offset, (dbm_t)*p,
> > &lentab[random() % lentablen], mode);
> > + pop_cur();
> > done = 1;
> > break;
> > }
> > diff --git a/man/man8/xfs_db.8 b/man/man8/xfs_db.8
> > index df54bb7..681efc4 100644
> > --- a/man/man8/xfs_db.8
> > +++ b/man/man8/xfs_db.8
> > @@ -232,7 +232,7 @@ enables verbose output. Messages will be printed for every block and
> > inode processed.
> > .RE
> > .TP
> > -.BI "blocktrash [\-n " count "] [\-x " min "] [\-y " max "] [\-s " seed "] [\-0|1|2|3] [\-t " type "] ..."
> > +.BI "blocktrash [-z] [\-o " offset "] [\-n " count "] [\-x " min "] [\-y " max "] [\-s " seed "] [\-0|1|2|3] [\-t " type "] ..."
> > Trash randomly selected filesystem metadata blocks.
> > Trashing occurs to randomly selected bits in the chosen blocks.
> > This command is available only in debugging versions of
> > @@ -259,6 +259,13 @@ supplies the
> > .I count
> > of block-trashings to perform (default 1).
> > .TP
> > +.B \-o
> > +supplies the bit
> > +.I offset
> > +at which to start trashing the block. If the value is preceded by a '+', the
> > +trashing will start at a randomly chosen offset that is larger than the value
> > +supplied. The default is to randomly choose an offset anywhere in the block.
> > +.TP
> > .B \-s
> > supplies a
> > .I seed
> > @@ -282,6 +289,12 @@ size of bit range to be trashed. The default value is 1.
> > sets the
> > .I maximum
> > size of bit range to be trashed. The default value is 1024.
> > +.TP
> > +.B \-z
> > +trashes the block at the top of the stack. It is not necessary to
> > +run
> > +.BI blockget
> > +if this option is supplied.
> > .RE
> > .TP
> > .BI "blockuse [\-n] [\-c " count ]
> >
> > _______________________________________________
> > xfs mailing list
> > xfs@oss.sgi.com
> > http://oss.sgi.com/mailman/listinfo/xfs
> >
>
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