Re: [PATCH] xfs_db: update sector size when type is set

[Bill O'Donnell <billodo@redhat.com>]

On Thu, Jun 22, 2017 at 03:16:27PM -0500, Eric Sandeen wrote:
> 
> 
> On 6/22/17 2:47 PM, Darrick J. Wong wrote:
> > On Thu, Jun 22, 2017 at 02:33:52PM -0500, Bill O'Donnell wrote:
> >> xfs_db doesn't take sector size into account when setting type.
> >> This can result in an errant crc. For example, with a sector size
> >> of 4096:
> >>
> >> xfs_db> agi 0
> >> xfs_db> p crc
> >> crc = 0xab85043e (correct)
> >> xfs_db> daddr
> >> current daddr is 16
> >> xfs_db> daddr 42
> >> xfs_db> daddr 16
> >> xfs_db> type agi
> >> Metadata CRC error detected at xfs_agi block 0x10/0x200
> >> xfs_db> p crc
> >> crc = 0xab85043e (bad)
> >>
> >> When xfs_db sets the new daddr in daddr_f, it does so with one
> >> BBSIZE sector (512). Changing the type doesn't change the size
> >> of the current buffer in iocur_top, so the checksum is calculated
> >> on the wrong length for the type (when the actual sector size > BBSIZE (512).
> >>
> >> For types with fields, reread the buffer to pick up the correct size for
> >> the new type when it gets set. Facilitate the reread by setting the cursor
> >> with set_cur().
> >>
> >> Signed-off-by: Bill O'Donnell <billodo@redhat.com>
> >> ---
> >>  db/io.c | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >> diff --git a/db/io.c b/db/io.c
> >> index 9918a51..7e6d330 100644
> >> --- a/db/io.c
> >> +++ b/db/io.c
> >> @@ -616,6 +616,12 @@ set_iocur_type(
> >>  {
> >>  	struct xfs_buf	*bp = iocur_top->bp;
> >>  
> 
> a comment about why only this "if" case is there would be good.

agreed.

> 
> >> +	if (t->fields)
> >> +		set_cur(t,
> >> +			iocur_top->bb,
> >> +			fsize(t->fields, iocur_top->data,
> >> +			      0, 0) / mp->m_sb.sb_blocksize,
> > 
> > I thought the third parameter to set_cur (which is fed as the third
> > parameter to libxfs_readbuf) was expressed in units of basic blocks
> > (i.e. 512 bytes)?  fsize returns the size of the field in bytes (I
> > think?), 
> 
> nope, bits :)
> 
> > so dividing by sb_blocksize renders units of fs blocks, not
> > basic blocks.
> 
> As Darrick just pointed out to me, you treated bits as bytes and
> daddr as fsblock so for 4k blocks, 8/8 came out right ;)

Yeah. Doh! I tested with sector sizes 512 and 4096 and it all just worked,
since mp->m_sb.sb_blocksize returned 1 and 8, respectively.

> 
> I think what you want for the size is something like:
> 
> BTOBB(byteize(fsize(t->fields, iocur_top->data, 0, 0)));
> 
> It might be a little nicer to stash that in a temp var so you
> don't have all that gunk in the call to set_cur.

Yep.


> > <shrug> the naming isn't helpful at all:
> > 
> > void
> > set_cur(
> > 	const typ_t	*t,
> > 	int64_t		d,
> > 	int		c,
> > ...
> > 	iocur_top->len = BBTOB(c);
> > 
> > <codeconfused>
> 
> yup isn't xfs_db fun?
> 
> > 
> > --D
> > 
> >> +			DB_RING_IGN, NULL);
> >>  	iocur_top->typ = t;
> >>  
> >>  	/* verify the buffer if the type has one. */
> >> -- 
> >> 2.9.4
> >>
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> >> the body of a message to majordomo@vger.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html