[Ocfs2-tools-devel] [PATCH] debugfs.ocfs2: fix dump_block_check for big-endian

[Joel Becker]

On Thu, Jul 28, 2011 at 06:50:46PM -0500, Goldwyn Rodrigues wrote:
> Hi Joel,
> 
> On Thu, Jul 28, 2011 at 5:20 AM, Joel Becker <jlbec at evilplan.org> wrote:
> > On Wed, Jul 06, 2011 at 05:19:39PM -0500, Goldwyn Rodrigues wrote:
> >> The block check or metaecc code expects the data to be in little-endian
> >> format for calculating CRC and ECC. However, with big-endian machines,
> >> the block is in big-endian format.
> >>
> >> Convert the block to little-endian format before feeding to meta ecc
> >> computation. After computing, change data format back to CPU.
> >>
> >
> >> ---
> >> diff --git a/debugfs.ocfs2/dump.c b/debugfs.ocfs2/dump.c
> >> index ad58126..d54c31a 100644
> >> --- a/debugfs.ocfs2/dump.c
> >> +++ b/debugfs.ocfs2/dump.c
> >> @@ -166,10 +166,74 @@ void dump_block_check(FILE *out, struct
> >> ocfs2_block_check *bc, void *block)
> >>  {
> >>       struct ocfs2_block_check tmp = *bc;
> >>       int crc_fail;
> >> +     enum dump_block_type bt = detect_block(block);
> >> +
> >> +     /* Swap block to little endian for compute_meta_ecc */
> >> +     switch (bt) {
> >> +             case DUMP_BLOCK_INODE:
> >> +                     ocfs2_swap_inode_from_cpu(gbls.fs, block);
> >> +                     break;
> >
> >        Instead, why not allocate a temporary block, copy the data over,
> > and then swap the temporary buffer.  That way you aren't having to swap
> > back?
> 
> Depends on what you consider more expensive: a memcpy of the block
> which happens in all archs, or a swap which is almost null for
> little-endian archs.

	This is debugfs.ocfs2.  There is no importance to the time taken
by a single memcpy().  We're not in a performance-intensive place.
	My concern is that swaping-and-back in place could have side
effects, eg in the case of corruption.

Joel

-- 

Life's Little Instruction Book #222

	"Think twice before burdening a friend with a secret."

			http://www.jlbec.org/
			jlbec at evilplan.org