[linux-lvm] A question about the metadata circular buffer

[Alasdair G Kergon]

On Fri, Dec 12, 2008 at 08:35:46PM +0800, yuan yuan wrote:
>     if ((new_wrap && old_wrap) ||
>             (rlocn && (new_wrap || old_wrap) && (new_end > rlocn->offset))
> ||
>             (mdac->rlocn.size >= mdah->size)) {
>                 log_error("VG %s metadata too large for circular buffer",
>                           vg->name);

> My question is , for a circular buffer, why should we check so many
> conditions instead of just checking (mdac->rlocn.size >= mdah->size)?

The buffer has to hold *two* versions of the metadata during a change,
the old and the new version, and those two could be different sizes.

Alasdair
-- 
agk at redhat.com