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

[Dave Chinner <david@fromorbit.com>]

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;

{}

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