netdev - Re: [patch net-next RFC 2/3] switchdev: allow caller to explicitly use deferred attr

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Date:	Fri, 9 Oct 2015 08:46:38 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Scott Feldman <sfeldma@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ido Schimmel <idosch@...lanox.com>, eladr@...lanox.com,
	Florian Fainelli <f.fainelli@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	"andrew@...n.ch" <andrew@...n.ch>,
	john fastabend <john.fastabend@...il.com>,
	David Laight <David.Laight@...lab.com>
Subject: Re: [patch net-next RFC 2/3] switchdev: allow caller to explicitly
 use deferred attr_set version

Fri, Oct 09, 2015 at 06:39:41AM CEST, sfeldma@...il.com wrote:
>On Thu, Oct 8, 2015 at 1:26 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>> Thu, Oct 08, 2015 at 08:03:35AM CEST, sfeldma@...il.com wrote:
>>>On Wed, Oct 7, 2015 at 10:39 PM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>> Thu, Oct 08, 2015 at 06:27:07AM CEST, sfeldma@...il.com wrote:
>>>>>On Wed, Oct 7, 2015 at 11:30 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>>>> From: Jiri Pirko <jiri@...lanox.com>
>>>>>>
>>>>>> Caller should know if he can call attr_set directly (when holding RTNL)
>>>>>> or if he has to use deferred version of this function.
>>>>>>
>>>>>> This also allows drivers to sleep inside attr_set and report operation
>>>>>> status back to switchdev core. Switchdev core then warns if status is
>>>>>> not ok, instead of silent errors happening in drivers.
>>>>>>
>>>>>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>>>>>> ---
>>>>>>  include/net/switchdev.h   |   2 +
>>>>>>  net/bridge/br_stp.c       |   4 +-
>>>>>>  net/switchdev/switchdev.c | 113 +++++++++++++++++++++++++---------------------
>>>>>>  3 files changed, 65 insertions(+), 54 deletions(-)
>>>>>>
>>>>>> diff --git a/include/net/switchdev.h b/include/net/switchdev.h
>>>>>> index 89266a3..320be44 100644
>>>>>> --- a/include/net/switchdev.h
>>>>>> +++ b/include/net/switchdev.h
>>>>>> @@ -168,6 +168,8 @@ int switchdev_port_attr_get(struct net_device *dev,
>>>>>>                             struct switchdev_attr *attr);
>>>>>>  int switchdev_port_attr_set(struct net_device *dev,
>>>>>>                             struct switchdev_attr *attr);
>>>>>> +int switchdev_port_attr_set_deferred(struct net_device *dev,
>>>>>> +                                    struct switchdev_attr *attr);
>>>>>
>>>>>Rather than adding another op, use attr->flags and define:
>>>>>
>>>>>#define SWITCHDEV_F_DEFERRED          BIT(x)
>>>>>
>>>>>So we get:
>>>>>
>>>>>void br_set_state(struct net_bridge_port *p, unsigned int state)
>>>>>{
>>>>>        struct switchdev_attr attr = {
>>>>>                .id = SWITCHDEV_ATTR_ID_PORT_STP_STATE,
>>>>>+              .flags = SWITCHDEV_F_DEFERRED,
>>>>>                .u.stp_state = state,
>>>>>        };
>>>>>        int err;
>>>>>
>>>>>        p->state = state;
>>>>>        err = switchdev_port_attr_set(p->dev, &attr);
>>>>>        if (err && err != -EOPNOTSUPP)
>>>>>                br_warn(p->br, "error setting offload STP state on
>>>>>port %u(%s)\n",
>>>>>                                (unsigned int) p->port_no,
>>>>>p->dev->name);
>>>>>}
>>>>>
>>>>>(And add obj->flags to do the same).
>>>>
>>>> That's what I wanted to avoid. Also because the obj is const and for
>>>> call from work, this flag would have to be removed.
>>>
>>>What did you want to avoid?
>>
>> Having this as a flag. I don't like it too much.
>> But that is cosmetics. Other than that, does the patchset make sense?
>> Do you see some possible issues?
>
>patch 1/3 makes sense, I tested it out and no issues.  (Looks like
>there are other places to assert rtnl_lock, are you going to add
>those?)

Sure, can you pinpoint the places?

>
>patch 2/3: Rather than trying to guess the call context in the core,
>make the caller call the right variant for its context.  That part is
>good.  On the flag vs. no flags, the reasons why I want this as a flag
>are:
>
>a) I want to keep the switchdev ops set to the core set: get/set attr
>and add/del/dump objs.  I've pushed back on changing this before.  I
>don't want ops explosion (like netdev_ops), and I'd like to avoid the
>1000-line patch when the arg list in an op changes, and we need to
>update N drivers.  The flags lets the caller modify the algo behavior,
>while keeping the core call (and args) fixed.
>
>b) the caller can combine flags, where it makes sense.  For example,
>maybe I'm in a locked context and I don't want to recurse the device
>tree, so I would make the call with NO_RECURSE | DEFERRED.  If we
>didn't use flags, then we need to supply ops for each variant on the
>call, and then things explode.

Fair enough. I'll process this in.


>
>patch 3/3 I haven't looked at yet...I'm stuck on 2/3.

It is very similar to 2/3, only for obj_add/del.
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