On Fri, Dec 17, 2010 at 3:02 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> On Fri, Dec 17, 2010 at 02:55:11PM -0500, William A. (Andy) Adamson wrote:
>> On Fri, Dec 17, 2010 at 2:33 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>> > On Fri, Dec 17, 2010 at 02:16:35PM -0500, William A. (Andy) Adamson wrote:
>> >> On Fri, Dec 17, 2010 at 2:10 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>> >> > On Fri, Dec 17, 2010 at 01:57:50PM -0500, William A. (Andy) Adamson wrote:
>> >> >> On Fri, Dec 17, 2010 at 1:54 PM, William A. (Andy) Adamson
>> >> >> <androsadamson@xxxxxxxxx> wrote:
>> >> >> > On Fri, Dec 17, 2010 at 1:40 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>> >> >> >> On Fri, Dec 17, 2010 at 01:20:02PM -0500, andros@xxxxxxxxxx wrote:
>> >> >> >>> From: Andy Adamson <andros@xxxxxxxxxx>
>> >> >> >>>
>> >> >> >>> Create a new transport for the shared back channel.l Move the current sock
>> >> >> >>> create and destroy routines into the new transport ops.
>> >> >> >>>
>> >> >> >>> Reference the back channel transport across message processing (recv/send).
>> >> >> >>>
>> >> >> >>> Signed-off-by: Andy Adamson <andros@xxxxxxxxxx>
>> >> >> >>> ---
>> >> >> >>> include/linux/sunrpc/svcsock.h | 1 +
>> >> >> >>> net/sunrpc/svc.c | 18 +++---
>> >> >> >>> net/sunrpc/svcsock.c | 122 +++++++++++++++++++++++++++++++++-------
>> >> >> >>> 3 files changed, 112 insertions(+), 29 deletions(-)
>> >> >> >>>
>> >> >> >>> diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
>> >> >> >>> index 1b353a7..3a45a80 100644
>> >> >> >>> --- a/include/linux/sunrpc/svcsock.h
>> >> >> >>> +++ b/include/linux/sunrpc/svcsock.h
>> >> >> >>> @@ -45,6 +45,7 @@ int svc_sock_names(struct svc_serv *serv, char *buf,
>> >> >> >>> int svc_addsock(struct svc_serv *serv, const int fd,
>> >> >> >>> char *name_return, const size_t len);
>> >> >> >>> void svc_init_xprt_sock(void);
>> >> >> >>> +void svc_init_bc_xprt_sock(void);
>> >> >> >>> void svc_cleanup_xprt_sock(void);
>> >> >> >>> struct svc_xprt *svc_sock_create(struct svc_serv *serv, int prot);
>> >> >> >>> void svc_sock_destroy(struct svc_xprt *);
>> >> >> >>> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
>> >> >> >>> index 6359c42..3520cb3 100644
>> >> >> >>> --- a/net/sunrpc/svc.c
>> >> >> >>> +++ b/net/sunrpc/svc.c
>> >> >> >>> @@ -488,10 +488,6 @@ svc_destroy(struct svc_serv *serv)
>> >> >> >>> if (svc_serv_is_pooled(serv))
>> >> >> >>> svc_pool_map_put();
>> >> >> >>>
>> >> >> >>> -#if defined(CONFIG_NFS_V4_1)
>> >> >> >>> - svc_sock_destroy(serv->bc_xprt);
>> >> >> >>> -#endif /* CONFIG_NFS_V4_1 */
>> >> >> >>> -
>> >> >> >>> svc_unregister(serv);
>> >> >> >>> kfree(serv->sv_pools);
>> >> >> >>> kfree(serv);
>> >> >> >>> @@ -1264,7 +1260,7 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
>> >> >> >>> {
>> >> >> >>> struct kvec *argv = &rqstp->rq_arg.head[0];
>> >> >> >>> struct kvec *resv = &rqstp->rq_res.head[0];
>> >> >> >>> - int error;
>> >> >> >>> + int ret;
>> >> >> >>>
>> >> >> >>> /* Build the svc_rqst used by the common processing routine */
>> >> >> >>> rqstp->rq_xprt = serv->bc_xprt;
>> >> >> >>> @@ -1292,12 +1288,16 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
>> >> >> >>> svc_getu32(argv); /* XID */
>> >> >> >>> svc_getnl(argv); /* CALLDIR */
>> >> >> >>>
>> >> >> >>> - error = svc_process_common(rqstp, argv, resv);
>> >> >> >>> - if (error <= 0)
>> >> >> >>> - return error;
>> >> >> >>> + /* Hold a reference to the back channel socket across the call */
>> >> >> >>> + svc_xprt_get(serv->bc_xprt);
>> >> >> >>
>> >> >> >> Either we already have a reference, in which case this is unnecessary,
>> >> >> >> or we don't, in which case this is risky.
>> >> >> >
>> >> >> > This is done so that when svc_xprt_put is called due to an svc_drop
>> >> >> > (svc_xprt_release, svc_xprt_put) it is not freed. It's not risky
>> >> >> > because AFAICS it's the way the rpc server code is intended to work.
>> >> >> > Note that svc_recv calls svc_xprt_get, and svc_send calls svc_xprt_put
>> >> >> > for the same reason.
>> >> >
>> >> > The svc_xprt_put()'s in svc_send/svc_drop balance the get in svc_recv().
>> >> > They're needed because on a normal server connections can come and go
>> >> > (because clients come and go) during the lifetime of the server.
>> >> >
>> >> > As I understand it, the client is just creating a new server for each
>> >> > backchannel. So the server will never outlive the one connection it
>> >> > uses. So you don't need that stuff. It's harmless--just leave it
>> >> > alone--but definitely don't try to add additional reference counting
>> >> > during the processing.
>> >>
>> >> If I don't add an svc_xprt_get prior to the svc_process_call, the
>> >> svc_xprt_put called in the svc_drop case will free the bc_xprt, which
>> >> is not what I want.
>> >
>> > Looking at the code some more.... Oh, right, because the backchannel
>> > doesn't call svc_recv, it calls its own bc_send, which doesn't do a put.
>> >
>> > Oh, yuch, I see: svc_process_common returns "1" to mean send, "0" to
>> > mean drop, and leaves it up to the caller to do the put in the send
>> > case. That's confusing.
>> >
>> > Maybe it would be simpler to have the caller be made responsible for
>> > both cases? So:
>> >
>> > if (svc_process_common(rqstp))
>> > send it
>> > else
>> > drop it
>>
>> That would work well. I'll send a patch
>
> If you do that you may want your own bc_svc_drop that doesn't bother
> with the put?
>
> You'd want to look through svc_xprt_release() to see if any of the rest
> of that makes sense in the bc case.
Yep :)
-->Andy
> --b.
>
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