[dm-devel] Re: [PATCH] dm snapshot: don't use zero chunksize
Alasdair G Kergon
agk at redhat.com
Wed Oct 7 23:36:31 UTC 2009
On Tue, Oct 06, 2009 at 07:01:37PM -0400, Mikulas Patocka wrote:
> Under some special conditions (too big chunk size or zero-sized device),
> the resulting hash_size is calculated as zero.
>
> rounddown_pow_of_two(0) is undefined operation (it expands to shift by -1).
> And init_exception_table with zero argument would fail with -ENOMEM.
>
> This patch makes minimum chunk size 64, just like for pending exception table.
Could we have some more specific information in this patch header?
How does a "too big" chunk size happen? And what is "too big"?
How does a zero-sized device happen and how can this code do anything
sensible if it encounters one - shouldn't it fail with an error instead?
Or do we still have a problem with the sequence in which dm ioctls are being
issued?
Alasdairs
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