On Mon 30 Jan 2017 05:14:41 PM CET, Alberto Garcia wrote:
> This patch keeps the index of the last used (i.e. non-zero) entry in
> the refcount table and updates it every time the table changes. The
> refcount-block overlap check then uses that index instead of reading
> the whole table.
Note that while I decided to go for this approach the patch can be made
much simpler by simply stopping at the first empty entry in the refcount
table:
if ((chk & QCOW2_OL_REFCOUNT_BLOCK) && s->refcount_table) {
for (i = 0; i < s->refcount_table_size; i++) {
if (!(s->refcount_table[i] & REFT_OFFSET_MASK)) {
break;
}
if (overlaps_with(s->refcount_table[i] & REFT_OFFSET_MASK,
s->cluster_size)) {
return QCOW2_OL_REFCOUNT_BLOCK;
}
}
}
I don't think QEMU produces files where refcount_table[i] == 0 but
refcount_table[i + 1] != 0. Do they even make sense? In any case, my
patch would cover those cases too, but this simplified version wouldn't.
Berto
