[dpdk-dev] [PATCH v4 06/24] ethdev: enable hotplug on multi-process

[Zhang, Qi Z]

> -----Original Message-----
> From: Burakov, Anatoly
> Sent: Tuesday, June 26, 2018 8:09 PM
> To: Zhang, Qi Z <qi.z.zhang at intel.com>; thomas at monjalon.net
> Cc: Ananyev, Konstantin <konstantin.ananyev at intel.com>; dev at dpdk.org;
> Richardson, Bruce <bruce.richardson at intel.com>; Yigit, Ferruh
> <ferruh.yigit at intel.com>; Shelton, Benjamin H
> <benjamin.h.shelton at intel.com>; Vangati, Narender
> <narender.vangati at intel.com>
> Subject: Re: [PATCH v4 06/24] ethdev: enable hotplug on multi-process
> 
> On 26-Jun-18 8:08 AM, Qi Zhang wrote:
> > We are going to introduce the solution to handle different hotplug
> > cases in multi-process situation, it include below scenario:
> >
> > 1. Attach a share device from primary
> > 2. Detach a share device from primary
> > 3. Attach a share device from secondary 4. Detach a share device from
> > secondary 5. Attach a private device from secondary 6. Detach a
> > private device from secondary 7. Detach a share device from secondary
> > privately 8. Attach a share device from secondary privately
> >
> > In primary-secondary process model, we assume device is shared by default.
> > that means attach or detach a device on any process will broadcast to
> > all other processes through mp channel then device information will be
> > synchronized on all processes.
> >
> > Any failure during attaching process will cause inconsistent status
> > between processes, so proper rollback action should be considered.
> > Also it is not safe to detach a share device when other process still
> > use it, so a handshake mechanism is introduced.
> >
> > This patch covers the implementation of case 1,2,5,6,7,8.
> > Case 3,4 will be implemented on separate patch as well as handshake
> > mechanism.
> >
> > Scenario for Case 1, 2:
> >
> > attach device
> > a) primary attach the new device if failed goto h).
> > b) primary send attach sync request to all secondary.
> > c) secondary receive request and attach device and send reply.
> > d) primary check the reply if all success go to i).
> > e) primary send attach rollback sync request to all secondary.
> > f) secondary receive the request and detach device and send reply.
> > g) primary receive the reply and detach device as rollback action.
> > h) attach fail
> > i) attach success
> >
> > detach device
> > a) primary perform pre-detach check, if device is locked, goto i).
> > b) primary send pre-detach sync request to all secondary.
> > c) secondary perform pre-detach check and send reply.
> > d) primary check the reply if any fail goto i).
> > e) primary send detach sync request to all secondary
> > f) secondary detach the device and send reply (assume no fail)
> > g) primary detach the device.
> > h) detach success
> > i) detach failed
> >
> > Case 5, 6:
> > Secondary process can attach private device which only visible to
> > itself, in this case no IPC is involved, primary process is not
> > allowed to have private device so far.
> >
> > Case 7, 8:
> > Secondary process can also temporally to detach a share device "privately"
> > then attach it back later, this action also not impact other processes.
> >
> > APIs changes:
> >
> > rte_eth_dev_attach and rte_eth_dev_attach are extended to support
> > share device attach/detach in primary-secondary process model, it will
> > be called in case 1,2,3,4.
> >
> > New API rte_eth_dev_attach_private and rte_eth_dev_detach_private are
> > introduced to cover case 5,6,7,8, this API can only be invoked in
> > secondary process.
> >
> > Signed-off-by: Qi Zhang <qi.z.zhang at intel.com>
> > ---
> 
> <snip>
> 
> > +static int
> > +handle_primary_request(const struct rte_mp_msg *msg, const void
> > +*peer) {
> > +
> > +	struct rte_mp_msg mp_resp;
> > +	const struct eth_dev_mp_req *req =
> > +		(const struct eth_dev_mp_req *)msg->param;
> > +	struct eth_dev_mp_req *resp =
> > +		(struct eth_dev_mp_req *)mp_resp.param;
> > +	struct mp_reply_bundle *bundle;
> > +	int ret = 0;
> > +
> > +	memset(&mp_resp, 0, sizeof(mp_resp));
> > +	strlcpy(mp_resp.name, ETH_DEV_MP_ACTION_REQUEST,
> sizeof(mp_resp.name));
> > +	mp_resp.len_param = sizeof(*req);
> > +	memcpy(resp, req, sizeof(*resp));
> > +
> > +	bundle = calloc(1, sizeof(*bundle));
> > +	if (bundle == NULL) {
> > +		resp->result = -ENOMEM;
> > +		ret = rte_mp_reply(&mp_resp, peer);
> > +		if (ret) {
> > +			ethdev_log(ERR, "failed to send reply to primary request\n");
> > +			return ret;
> > +		}
> > +	}
> > +
> > +	bundle->msg = *msg;
> > +	bundle->peer = peer;
> > +
> > +	ret = rte_eal_mp_task_add(__handle_primary_request, bundle);
> > +	if (ret) {
> > +		resp->result = ret;
> > +		ret = rte_mp_reply(&mp_resp, peer);
> > +		if (ret) {
> > +			ethdev_log(ERR, "failed to send reply to primary request\n");
> > +			return ret;
> > +		}
> > +	}
> 
> What you're doing here is quite dangerous. The parameter "const void *peer"
> is only guaranteed to be valid at the time of the callback - not necessarily
> afterwards. So, if you're handing off sending replies to a separate thread,
> things might blow up because the pointer may no longer be valid.

OK, so what about clone the content a buffer, I think the content should be valid before reply is sent, right?

Thanks
Qi
> 
> --
> Thanks,
> Anatoly