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

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

On Thu, Jun 22, 2017 at 12:47:23PM -0700, 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;
> >  
> > +	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?), so dividing by sb_blocksize renders units of fs blocks, not
> basic blocks.
> 

fsize returns the field size in bits. Dividing by sb_blocksize gives basic blocks.

> <shrug> the naming isn't helpful at all:

I also found the naming through the call stack to be terrible and damned
confusing (c, d ? really??), but left that battle for another day, another
patch. ;)

Thanks-
Bill

> 
> void
> set_cur(
> 	const typ_t	*t,
> 	int64_t		d,
> 	int		c,
> ...
> 	iocur_top->len = BBTOB(c);
> 
> <codeconfused>
> 
> --D
> 
> > +			DB_RING_IGN, NULL);
> >  	iocur_top->typ = t;
> >  
> >  	/* verify the buffer if the type has one. */
> > -- 
> > 2.9.4
> > 
> > --
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