Re: [PATCH] xfs_logprint: Fix super block buffer interpretation issue

[Chi Zhiling]

On 2024/10/11 11:24, Darrick J. Wong wrote:
> On Fri, Oct 11, 2024 at 11:08:10AM +0800, Chi Zhiling wrote:
> > From: chizhiling <chizhiling@xxxxxxxxxx>
> >
> > When using xfs_logprint to interpret the buffer of the super block, the
> > icount will always be 6360863066640355328 (0x5846534200001000). This is
> > because the offset of icount is incorrect, causing xfs_logprint to
> > misinterpret the MAGIC number as icount.
> > This patch fixes the offset value of the SB counters in xfs_logprint.
> >
> > Before this patch:
> > icount: 6360863066640355328  ifree: 5242880  fdblks: 0  frext: 0
> >
> > After this patch:
> > icount: 10240  ifree: 4906  fdblks: 37  frext: 0
> >
> > Signed-off-by: chizhiling <chizhiling@xxxxxxxxxx>
> > ---
> >   logprint/log_misc.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/logprint/log_misc.c b/logprint/log_misc.c
> > index 8e86ac34..21da5b8b 100644
> > --- a/logprint/log_misc.c
> > +++ b/logprint/log_misc.c
> > @@ -288,13 +288,13 @@ xlog_print_trans_buffer(char **ptr, int len, int *i, int num_ops)
> >   			/*
> >   			 * memmove because *ptr may not be 8-byte aligned
> >   			 */
> > -			memmove(&a, *ptr, sizeof(__be64));
> > -			memmove(&b, *ptr+8, sizeof(__be64));
> How did this ever work??  This even looks wrong in "Release_1.0.0".
Yes, I was surprised when I find this issue
> > +			memmove(&a, *ptr + offsetof(struct xfs_dsb, sb_icount), sizeof(__be64));
> > +			memmove(&b, *ptr + offsetof(struct xfs_dsb, sb_ifree), sizeof(__be64));
> Why not do:
>
> 			struct xfs_dsb *dsb = *ptr;
>
> 			memcpy(&a, &dsb->sb_icount, sizeof(a));
>
> or better yet, skip the indirection and do
>
> 			printf(_("icount: %llu  ifree: %llu  "),
> 					(unsigned long long)be64_to_cpu(dsb->sb_icount),
> 					(unsigned long long)be64_to_cpu(dsb->sb_ifree));
>
> Hm?

Yes, of course we can do it this way, I just want the fix patch to look 
smaller :)

I think both ok.


chi

> --D
>
> >   			printf(_("icount: %llu  ifree: %llu  "),
> >   			       (unsigned long long) be64_to_cpu(a),
> >   			       (unsigned long long) be64_to_cpu(b));
> > -			memmove(&a, *ptr+16, sizeof(__be64));
> > -			memmove(&b, *ptr+24, sizeof(__be64));
> > +			memmove(&a, *ptr + offsetof(struct xfs_dsb, sb_fdblocks), sizeof(__be64));
> > +			memmove(&b, *ptr + offsetof(struct xfs_dsb, sb_frextents), sizeof(__be64));
> >   			printf(_("fdblks: %llu  frext: %llu\n"),
> >   			       (unsigned long long) be64_to_cpu(a),
> >   			       (unsigned long long) be64_to_cpu(b));
> > --
> > 2.43.0