On Fri, May 16, 2014 at 02:12:46PM -0400, Brian Foster wrote:
> Create sysfs attributes to export the current runtime state of the log
> to userspace. Note that the filesystem should be frozen for best
> accuracy/consistency when reading these values, but is not required.
> This is for testing and debug purposes only.
> Create the following per-mount attributes: log_head_lsn, log_tail_lsn,
> reserve_head_lsn and write_head_lsn. These represent the physical log
Reserve and write heads are not log sequence numbers (LSNs). A LSN
is a cycle:block count tuple, while a grant head is a cycle:byte
Calling the reserve_grant_head/write_grant_head would make more
sense, I think, as would splitting them into cycle/byte output
pairs. Splitting them make sense because if we increase the log size
beyond 2GB we're going to need a different in-memory representation
for the grant heads (i.e. need more than 32 bits for byte count), so
we should probably handle that up front in the sysfs API...