Re: [PATCH 2/4] xfs_db: use iocursor type to guess btree geometry if bad magic

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Apr 11, 2017 at 10:03:32AM +1000, Dave Chinner wrote:
> On Mon, Apr 10, 2017 at 03:47:53PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > The function block_to_bt plays an integral role in determining the btree
> > geometry of a block that we want to manipulate with the debugger.
> > Normally we use the block magic to find the geometry profile, but if the
> > magic is bad we'll never find it and return NULL.  The callers of this
> > function do not check for NULL and crash.
> > 
> > Therefore, if we can't find a geometry profile matching the magic
> > number, use the iocursor type to guess the profile and scowl about that
> > to stdout.  This makes it so that even with a corrupt magic we can try
> > to print the fields instead of crashing the debugger.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > v2: be less macro-happy and only evaluate hascrc once
> > ---
> >  db/btblock.c |   52 ++++++++++++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 44 insertions(+), 8 deletions(-)
> > 
> > 
> > diff --git a/db/btblock.c b/db/btblock.c
> > index 835a5f0..e494f3e 100644
> > --- a/db/btblock.c
> > +++ b/db/btblock.c
> > @@ -25,6 +25,8 @@
> >  #include "print.h"
> >  #include "bit.h"
> >  #include "init.h"
> > +#include "io.h"
> > +#include "output.h"
> >  
> >  /*
> >   * Definition of the possible btree block layouts.
> > @@ -122,13 +124,50 @@ static struct xfs_db_btree *
> >  block_to_bt(
> >  	struct xfs_btree_block	*bb)
> >  {
> > -	struct xfs_db_btree *btp = &btrees[0];
> > +	struct xfs_db_btree	*btp;
> > +	uint32_t		magic;
> > +	bool			crc;
> > +
> > +	magic = be32_to_cpu((bb)->bb_magic);
> > +	for (btp = &btrees[0]; btp->magic != 0; btp++)
> > +		if (magic == btp->magic)
> > +			return btp;
> 
> {}

Sure.

--D

> 
> -Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> --
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