On Fri, Dec 22, 2017 at 09:25:53AM -0500, J. Bruce Fields wrote:
> On Fri, Dec 22, 2017 at 09:29:15AM +0000, Reshetova, Elena wrote:
> >
> > On Wed, Nov 29, 2017 at 01:15:43PM +0200, Elena Reshetova wrote:
> > > atomic_t variables are currently used to implement reference
> > > counters with the following properties:
> > > - counter is initialized to 1 using atomic_set()
> > > - a resource is freed upon counter reaching zero
> > > - once counter reaches zero, its further
> > > increments aren't allowed
> > > - counter schema uses basic atomic operations
> > > (set, inc, inc_not_zero, dec_and_test, etc.)
> >
> > >Whoops, I forgot that this doesn't apply to h_count.
> >
> > >Well, it's confusing, because h_count is actually used in two different
> > >ways: depending on whether a nlm_host represents a client or server, it
> > >may have the above properties or not.
> >
> >
> > So, what happens when it is not having the above properties? Is the object
> > being reused or?
>
> The object isn't destroyed when the counter hits zero--zero is just
> taken as a hint to some garbage collection algorithm that it would be OK
> to destroy it. So decrementing to or incrementing from zero is OK.
In more detail: the nlm_host objects that are used on the NFS server to
represent NFS clients are put by nlmsvc_release_host, and then may
eventually be freed by nlm_gc_hosts.
The nlm_host objects that are used on the NFS client to represent NFS
servers are put (and freed when h_count goes to zero) by
nlmclnt_release_host.
In both cases reference are taken by nlm_get_host. It would be possible
to replace nlm_get_host by two different functions if that would help.
Most callers are obviously only client-side or server-side. The only
exception is next_host_state. It could be passed a pointer to the "get"
function it should use.
After that we might actually just want to define separate client and
server structs like:
struct nlm_clnt_host {
struct nlm_host ch_host;
refcount_t ch_count;
...
}
struct nlm_srv_host {
struct nlm_host sh_host;
refcount_t sh_count;
...
}
rather than have a single h_count which is used in two confusingly
different ways. There are also some other nlm_host fields that really
only make sense for client or server.
--b.
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