On Thursday 13 May 2004 18:30, Dave Olien wrote: > I'm using your udm1 patch set to linux 2.6.6-rc2. > The man page for lvcreate says the chunksize parameter for a > snapshot can be a power of two value between 4k and 1024k. > > When I try --chunksize 1024, I hit a BUG() in the bvec_index() > function. > > Putting some checking code into snapshot_ctr(), I observe that > when the lvcreate --chunksize 1024 parameter is used, snapshot_ctr() > reports a chunksize of 2048. This is the value just after the > simple_strtoul() call. > > So, why is the value being doubled (by the lvcreate command?). The value isn't being doubled. dm-snapshot expects the chunk-size value in sectors, whereas the user-space tools present the option in kilobytes. So....I guess the value *is* being doubled, but for the right reason. > Also, why is there no range check on the value in snapshot_ctr(), > with a error code failure, rather than a BUG() call in bvec_index? So it seems there are some implicit limits when using the dm-io APIs. For the time being, we might need to add a size check in dm-snapshot to prevent chunk-sizes greater than 512kB. We should also review the dm-io code to see if these limitations are real, or if there's a way to get around them. -- Kevin Corry kevincorry@xxxxxxxxxxxxx
