On Tue, Mar 18, 2008 at 01:22:54AM +0800, Andreas Dilger wrote:
> On Mar 17, 2008 09:28 -0400, Theodore Ts'o wrote:
> > +STATIC __u16 ext2fs_group_desc_csum(ext2_filsys fs, dgrp_t group)
....
> > + if (fs->super->s_feature_ro_compat & EXT4_FEATURE_RO_COMPAT_GDT_CSUM) {
> > + int offset = offsetof(struct ext2_group_desc, bg_checksum);
> > +
...
> > + offset += sizeof(desc->bg_checksum); /* skip checksum */
> > + assert(offset == sizeof(*desc));
>
> Note that this assertion needs to be removed when the group descriptor
> becomes larger, unless ext2_group_desc never changes in the future..
Yeah, I looked at this, and was half tempted to remove it.
Indeed ext2_group_desc will never change in the future. Too many
things would break if we change it. That's why there is an
ext4_group_desc which looks exactly like ext2_group_desc for the first
32 bytes, and adds the high 32-bits for the various fields in the
second 32-bytes.
But if ext2_group_desc is never going to change, then there's no real
good reason to use a run-time check here. Better to turn it into a
compile time check, using #error. The tricky part is doing it in a
way which is ANSI-C compliant (or maybe we just wrap it in a #ifdef
GCC and only do the sanity check if you are compiling with GCC).
- Ted
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