[dm-devel] Chunk size, mask and shift

[Guilherme Moro <guilherme moro gmail com>]

hello,

Im trying to understand the dm-snapshot target, but Im not sure how it uses the size, mask and shift of the chunks, not sure if I understand it correctly.

Can anyone give an overall idea of why they are initialized this way 

store->chunk_size = chunk_size_ulong;
store->chunk_mask = chunk_size_ulong - 1;
store->chunk_shift = ffs(chunk_size_ulong) - 1;

and why use this to translate sector to chunks 

static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
                      sector_t sector)
{
    return (sector & ~store->chunk_mask) >> store->chunk_shift;
}

thanks,

Guilherme Moro