[PATCH][V2] libbpf: add support for canceling cached_cons advance

[PATCH][V2] libbpf: add support for canceling cached_cons advance

[Li RongQing]

Add a new function for returning descriptors the user received
after an xsk_ring_cons__peek call. After the application has
gotten a number of descriptors from a ring, it might not be able
to or want to process them all for various reasons. Therefore,
it would be useful to have an interface for returning or
cancelling a number of them so that they are returned to the ring.

This patch adds a new function called xsk_ring_cons__cancel that
performs this operation on nb descriptors counted from the end of
the batch of descriptors that was received through the peek call.

Signed-off-by: Li RongQing <lirongqing@baidu.com>
[ Magnus Karlsson: rewrote changelog ]
Cc: Magnus Karlsson <magnus.karlsson@intel.com>
---
diff with v1: fix the building, and rewrote changelog

 tools/lib/bpf/xsk.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
index 1069c46364ff..1719a327e5f9 100644
--- a/tools/lib/bpf/xsk.h
+++ b/tools/lib/bpf/xsk.h
@@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
 	return entries;
 }
 
+static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
+					 size_t nb)
+{
+	cons->cached_cons -= nb;
+}
+
 static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
 {
 	/* Make sure data has been read before indicating we are done
-- 
2.17.3

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Magnus Karlsson]

On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
>
> Add a new function for returning descriptors the user received
> after an xsk_ring_cons__peek call. After the application has
> gotten a number of descriptors from a ring, it might not be able
> to or want to process them all for various reasons. Therefore,
> it would be useful to have an interface for returning or
> cancelling a number of them so that they are returned to the ring.
>
> This patch adds a new function called xsk_ring_cons__cancel that
> performs this operation on nb descriptors counted from the end of
> the batch of descriptors that was received through the peek call.
>
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> [ Magnus Karlsson: rewrote changelog ]
> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
> ---
> diff with v1: fix the building, and rewrote changelog
>
>  tools/lib/bpf/xsk.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> index 1069c46364ff..1719a327e5f9 100644
> --- a/tools/lib/bpf/xsk.h
> +++ b/tools/lib/bpf/xsk.h
> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
>         return entries;
>  }
>
> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
> +                                        size_t nb)
> +{
> +       cons->cached_cons -= nb;
> +}
> +
>  static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>  {
>         /* Make sure data has been read before indicating we are done
> --
> 2.17.3

Thank you RongQing.

Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Daniel Borkmann]

On 11/24/20 9:12 AM, Magnus Karlsson wrote:
> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
>>
>> Add a new function for returning descriptors the user received
>> after an xsk_ring_cons__peek call. After the application has
>> gotten a number of descriptors from a ring, it might not be able
>> to or want to process them all for various reasons. Therefore,
>> it would be useful to have an interface for returning or
>> cancelling a number of them so that they are returned to the ring.
>>
>> This patch adds a new function called xsk_ring_cons__cancel that
>> performs this operation on nb descriptors counted from the end of
>> the batch of descriptors that was received through the peek call.
>>
>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
>> [ Magnus Karlsson: rewrote changelog ]
>> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
>> ---
>> diff with v1: fix the building, and rewrote changelog
>>
>>   tools/lib/bpf/xsk.h | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
>> index 1069c46364ff..1719a327e5f9 100644
>> --- a/tools/lib/bpf/xsk.h
>> +++ b/tools/lib/bpf/xsk.h
>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
>>          return entries;
>>   }
>>
>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
>> +                                        size_t nb)
>> +{
>> +       cons->cached_cons -= nb;
>> +}
>> +
>>   static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>>   {
>>          /* Make sure data has been read before indicating we are done
>> --
>> 2.17.3
> 
> Thank you RongQing.
> 
> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

@Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?

Thanks,
Daniel

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Magnus Karlsson]

On Tue, Nov 24, 2020 at 10:58 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 11/24/20 9:12 AM, Magnus Karlsson wrote:
> > On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
> >>
> >> Add a new function for returning descriptors the user received
> >> after an xsk_ring_cons__peek call. After the application has
> >> gotten a number of descriptors from a ring, it might not be able
> >> to or want to process them all for various reasons. Therefore,
> >> it would be useful to have an interface for returning or
> >> cancelling a number of them so that they are returned to the ring.
> >>
> >> This patch adds a new function called xsk_ring_cons__cancel that
> >> performs this operation on nb descriptors counted from the end of
> >> the batch of descriptors that was received through the peek call.
> >>
> >> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> >> [ Magnus Karlsson: rewrote changelog ]
> >> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
> >> ---
> >> diff with v1: fix the building, and rewrote changelog
> >>
> >>   tools/lib/bpf/xsk.h | 6 ++++++
> >>   1 file changed, 6 insertions(+)
> >>
> >> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> >> index 1069c46364ff..1719a327e5f9 100644
> >> --- a/tools/lib/bpf/xsk.h
> >> +++ b/tools/lib/bpf/xsk.h
> >> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
> >>          return entries;
> >>   }
> >>
> >> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
> >> +                                        size_t nb)
> >> +{
> >> +       cons->cached_cons -= nb;
> >> +}
> >> +
> >>   static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
> >>   {
> >>          /* Make sure data has been read before indicating we are done
> >> --
> >> 2.17.3
> >
> > Thank you RongQing.
> >
> > Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
>
> @Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?

All the other interfaces have size_t as the type for "nb". It is kind
of weird as a __u32 would have made more sense, but cannot actually
remember why I chose a size_t two years ago. But for consistency with
the other interfaces, let us keep it a size_t for now. I will do some
research around the reason.

> Thanks,
> Daniel

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Daniel Borkmann]

On 11/25/20 9:30 AM, Magnus Karlsson wrote:
> On Tue, Nov 24, 2020 at 10:58 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>> On 11/24/20 9:12 AM, Magnus Karlsson wrote:
>>> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
>>>>
>>>> Add a new function for returning descriptors the user received
>>>> after an xsk_ring_cons__peek call. After the application has
>>>> gotten a number of descriptors from a ring, it might not be able
>>>> to or want to process them all for various reasons. Therefore,
>>>> it would be useful to have an interface for returning or
>>>> cancelling a number of them so that they are returned to the ring.
>>>>
>>>> This patch adds a new function called xsk_ring_cons__cancel that
>>>> performs this operation on nb descriptors counted from the end of
>>>> the batch of descriptors that was received through the peek call.
>>>>
>>>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
>>>> [ Magnus Karlsson: rewrote changelog ]
>>>> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
>>>> ---
>>>> diff with v1: fix the building, and rewrote changelog
>>>>
>>>>    tools/lib/bpf/xsk.h | 6 ++++++
>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
>>>> index 1069c46364ff..1719a327e5f9 100644
>>>> --- a/tools/lib/bpf/xsk.h
>>>> +++ b/tools/lib/bpf/xsk.h
>>>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
>>>>           return entries;
>>>>    }
>>>>
>>>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
>>>> +                                        size_t nb)
>>>> +{
>>>> +       cons->cached_cons -= nb;
>>>> +}
>>>> +
>>>>    static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>>>>    {
>>>>           /* Make sure data has been read before indicating we are done
>>>> --
>>>> 2.17.3
>>>
>>> Thank you RongQing.
>>>
>>> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
>>
>> @Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?
> 
> All the other interfaces have size_t as the type for "nb". It is kind
> of weird as a __u32 would have made more sense, but cannot actually
> remember why I chose a size_t two years ago. But for consistency with
> the other interfaces, let us keep it a size_t for now. I will do some
> research around the reason.

It's actually a bit of a mix currently which is what got me confused:

static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod *prod, size_t nb, __u32 *idx)
static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, size_t nb, __u32 *idx)
static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)

(I can take it in as-is, but would be nice to clean it up a bit to avoid confusion.)

Thanks,
Daniel

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Magnus Karlsson]

On Wed, Nov 25, 2020 at 10:02 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 11/25/20 9:30 AM, Magnus Karlsson wrote:
> > On Tue, Nov 24, 2020 at 10:58 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
> >> On 11/24/20 9:12 AM, Magnus Karlsson wrote:
> >>> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
> >>>>
> >>>> Add a new function for returning descriptors the user received
> >>>> after an xsk_ring_cons__peek call. After the application has
> >>>> gotten a number of descriptors from a ring, it might not be able
> >>>> to or want to process them all for various reasons. Therefore,
> >>>> it would be useful to have an interface for returning or
> >>>> cancelling a number of them so that they are returned to the ring.
> >>>>
> >>>> This patch adds a new function called xsk_ring_cons__cancel that
> >>>> performs this operation on nb descriptors counted from the end of
> >>>> the batch of descriptors that was received through the peek call.
> >>>>
> >>>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> >>>> [ Magnus Karlsson: rewrote changelog ]
> >>>> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
> >>>> ---
> >>>> diff with v1: fix the building, and rewrote changelog
> >>>>
> >>>>    tools/lib/bpf/xsk.h | 6 ++++++
> >>>>    1 file changed, 6 insertions(+)
> >>>>
> >>>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> >>>> index 1069c46364ff..1719a327e5f9 100644
> >>>> --- a/tools/lib/bpf/xsk.h
> >>>> +++ b/tools/lib/bpf/xsk.h
> >>>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
> >>>>           return entries;
> >>>>    }
> >>>>
> >>>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
> >>>> +                                        size_t nb)
> >>>> +{
> >>>> +       cons->cached_cons -= nb;
> >>>> +}
> >>>> +
> >>>>    static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
> >>>>    {
> >>>>           /* Make sure data has been read before indicating we are done
> >>>> --
> >>>> 2.17.3
> >>>
> >>> Thank you RongQing.
> >>>
> >>> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
> >>
> >> @Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?
> >
> > All the other interfaces have size_t as the type for "nb". It is kind
> > of weird as a __u32 would have made more sense, but cannot actually
> > remember why I chose a size_t two years ago. But for consistency with
> > the other interfaces, let us keep it a size_t for now. I will do some
> > research around the reason.
>
> It's actually a bit of a mix currently which is what got me confused:
>
> static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
> static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
> static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod *prod, size_t nb, __u32 *idx)
> static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
> static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, size_t nb, __u32 *idx)
> static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>
> (I can take it in as-is, but would be nice to clean it up a bit to avoid confusion.)

Hmm, that is confusing indeed. Well, the best choice would be __u32
everywhere since the ring pointers themselves are __u32. But I am
somewhat afraid of changing an API. Can we guarantee that a change
from size_t to __u32 will not break some user's compilation? Another
option would be to clean this up next year when we will very likely
produce a 1.0 version of this API and at that point we can change some
things. What do you think would be the best approach?

> Thanks,
> Daniel

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Daniel Borkmann]

On 11/25/20 10:13 AM, Magnus Karlsson wrote:
> On Wed, Nov 25, 2020 at 10:02 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>> On 11/25/20 9:30 AM, Magnus Karlsson wrote:
>>> On Tue, Nov 24, 2020 at 10:58 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>>> On 11/24/20 9:12 AM, Magnus Karlsson wrote:
>>>>> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
>>>>>>
>>>>>> Add a new function for returning descriptors the user received
>>>>>> after an xsk_ring_cons__peek call. After the application has
>>>>>> gotten a number of descriptors from a ring, it might not be able
>>>>>> to or want to process them all for various reasons. Therefore,
>>>>>> it would be useful to have an interface for returning or
>>>>>> cancelling a number of them so that they are returned to the ring.
>>>>>>
>>>>>> This patch adds a new function called xsk_ring_cons__cancel that
>>>>>> performs this operation on nb descriptors counted from the end of
>>>>>> the batch of descriptors that was received through the peek call.
>>>>>>
>>>>>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
>>>>>> [ Magnus Karlsson: rewrote changelog ]
>>>>>> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
>>>>>> ---
>>>>>> diff with v1: fix the building, and rewrote changelog
>>>>>>
>>>>>>     tools/lib/bpf/xsk.h | 6 ++++++
>>>>>>     1 file changed, 6 insertions(+)
>>>>>>
>>>>>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
>>>>>> index 1069c46364ff..1719a327e5f9 100644
>>>>>> --- a/tools/lib/bpf/xsk.h
>>>>>> +++ b/tools/lib/bpf/xsk.h
>>>>>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
>>>>>>            return entries;
>>>>>>     }
>>>>>>
>>>>>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
>>>>>> +                                        size_t nb)
>>>>>> +{
>>>>>> +       cons->cached_cons -= nb;
>>>>>> +}
>>>>>> +
>>>>>>     static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>>>>>>     {
>>>>>>            /* Make sure data has been read before indicating we are done
>>>>>> --
>>>>>> 2.17.3
>>>>>
>>>>> Thank you RongQing.
>>>>>
>>>>> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
>>>>
>>>> @Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?
>>>
>>> All the other interfaces have size_t as the type for "nb". It is kind
>>> of weird as a __u32 would have made more sense, but cannot actually
>>> remember why I chose a size_t two years ago. But for consistency with
>>> the other interfaces, let us keep it a size_t for now. I will do some
>>> research around the reason.
>>
>> It's actually a bit of a mix currently which is what got me confused:
>>
>> static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
>> static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
>> static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod *prod, size_t nb, __u32 *idx)
>> static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
>> static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, size_t nb, __u32 *idx)
>> static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>>
>> (I can take it in as-is, but would be nice to clean it up a bit to avoid confusion.)
> 
> Hmm, that is confusing indeed. Well, the best choice would be __u32
> everywhere since the ring pointers themselves are __u32. But I am
> somewhat afraid of changing an API. Can we guarantee that a change
> from size_t to __u32 will not break some user's compilation? Another
> option would be to clean this up next year when we will very likely
> produce a 1.0 version of this API and at that point we can change some
> things. What do you think would be the best approach?

Given they're all inlines, imho, risk should be fairly low to switch all to __u32.
I would probably go and verify first with DPDK as main user of the lib and/or write
some test cases to see if compiler spills any new warnings and the like, but if not
the case then we should do it for bpf-next so this has plenty of exposure in the
meantime. Any nb large than u32 max is a bug in any case.

Thanks,
Daniel

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Magnus Karlsson]

On Wed, Nov 25, 2020 at 11:07 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 11/25/20 10:13 AM, Magnus Karlsson wrote:
> > On Wed, Nov 25, 2020 at 10:02 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
> >> On 11/25/20 9:30 AM, Magnus Karlsson wrote:
> >>> On Tue, Nov 24, 2020 at 10:58 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
> >>>> On 11/24/20 9:12 AM, Magnus Karlsson wrote:
> >>>>> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
> >>>>>>
> >>>>>> Add a new function for returning descriptors the user received
> >>>>>> after an xsk_ring_cons__peek call. After the application has
> >>>>>> gotten a number of descriptors from a ring, it might not be able
> >>>>>> to or want to process them all for various reasons. Therefore,
> >>>>>> it would be useful to have an interface for returning or
> >>>>>> cancelling a number of them so that they are returned to the ring.
> >>>>>>
> >>>>>> This patch adds a new function called xsk_ring_cons__cancel that
> >>>>>> performs this operation on nb descriptors counted from the end of
> >>>>>> the batch of descriptors that was received through the peek call.
> >>>>>>
> >>>>>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> >>>>>> [ Magnus Karlsson: rewrote changelog ]
> >>>>>> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
> >>>>>> ---
> >>>>>> diff with v1: fix the building, and rewrote changelog
> >>>>>>
> >>>>>>     tools/lib/bpf/xsk.h | 6 ++++++
> >>>>>>     1 file changed, 6 insertions(+)
> >>>>>>
> >>>>>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> >>>>>> index 1069c46364ff..1719a327e5f9 100644
> >>>>>> --- a/tools/lib/bpf/xsk.h
> >>>>>> +++ b/tools/lib/bpf/xsk.h
> >>>>>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
> >>>>>>            return entries;
> >>>>>>     }
> >>>>>>
> >>>>>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
> >>>>>> +                                        size_t nb)
> >>>>>> +{
> >>>>>> +       cons->cached_cons -= nb;
> >>>>>> +}
> >>>>>> +
> >>>>>>     static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
> >>>>>>     {
> >>>>>>            /* Make sure data has been read before indicating we are done
> >>>>>> --
> >>>>>> 2.17.3
> >>>>>
> >>>>> Thank you RongQing.
> >>>>>
> >>>>> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
> >>>>
> >>>> @Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?
> >>>
> >>> All the other interfaces have size_t as the type for "nb". It is kind
> >>> of weird as a __u32 would have made more sense, but cannot actually
> >>> remember why I chose a size_t two years ago. But for consistency with
> >>> the other interfaces, let us keep it a size_t for now. I will do some
> >>> research around the reason.
> >>
> >> It's actually a bit of a mix currently which is what got me confused:
> >>
> >> static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
> >> static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
> >> static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod *prod, size_t nb, __u32 *idx)
> >> static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
> >> static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, size_t nb, __u32 *idx)
> >> static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
> >>
> >> (I can take it in as-is, but would be nice to clean it up a bit to avoid confusion.)
> >
> > Hmm, that is confusing indeed. Well, the best choice would be __u32
> > everywhere since the ring pointers themselves are __u32. But I am
> > somewhat afraid of changing an API. Can we guarantee that a change
> > from size_t to __u32 will not break some user's compilation? Another
> > option would be to clean this up next year when we will very likely
> > produce a 1.0 version of this API and at that point we can change some
> > things. What do you think would be the best approach?
>
> Given they're all inlines, imho, risk should be fairly low to switch all to __u32.
> I would probably go and verify first with DPDK as main user of the lib and/or write
> some test cases to see if compiler spills any new warnings and the like, but if not
> the case then we should do it for bpf-next so this has plenty of exposure in the
> meantime. Any nb large than u32 max is a bug in any case.

Sounds good. Will do and get back to you.

> Thanks,
> Daniel

Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Daniel Borkmann]

On 11/25/20 11:09 AM, Magnus Karlsson wrote:
> On Wed, Nov 25, 2020 at 11:07 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>
>> On 11/25/20 10:13 AM, Magnus Karlsson wrote:
>>> On Wed, Nov 25, 2020 at 10:02 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>>> On 11/25/20 9:30 AM, Magnus Karlsson wrote:
>>>>> On Tue, Nov 24, 2020 at 10:58 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>>>>> On 11/24/20 9:12 AM, Magnus Karlsson wrote:
>>>>>>> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
>>>>>>>>
>>>>>>>> Add a new function for returning descriptors the user received
>>>>>>>> after an xsk_ring_cons__peek call. After the application has
>>>>>>>> gotten a number of descriptors from a ring, it might not be able
>>>>>>>> to or want to process them all for various reasons. Therefore,
>>>>>>>> it would be useful to have an interface for returning or
>>>>>>>> cancelling a number of them so that they are returned to the ring.
>>>>>>>>
>>>>>>>> This patch adds a new function called xsk_ring_cons__cancel that
>>>>>>>> performs this operation on nb descriptors counted from the end of
>>>>>>>> the batch of descriptors that was received through the peek call.
>>>>>>>>
>>>>>>>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
>>>>>>>> [ Magnus Karlsson: rewrote changelog ]
>>>>>>>> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
>>>>>>>> ---
>>>>>>>> diff with v1: fix the building, and rewrote changelog
>>>>>>>>
>>>>>>>>      tools/lib/bpf/xsk.h | 6 ++++++
>>>>>>>>      1 file changed, 6 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
>>>>>>>> index 1069c46364ff..1719a327e5f9 100644
>>>>>>>> --- a/tools/lib/bpf/xsk.h
>>>>>>>> +++ b/tools/lib/bpf/xsk.h
>>>>>>>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
>>>>>>>>             return entries;
>>>>>>>>      }
>>>>>>>>
>>>>>>>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
>>>>>>>> +                                        size_t nb)
>>>>>>>> +{
>>>>>>>> +       cons->cached_cons -= nb;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>>      static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>>>>>>>>      {
>>>>>>>>             /* Make sure data has been read before indicating we are done
>>>>>>>> --
>>>>>>>> 2.17.3
>>>>>>>
>>>>>>> Thank you RongQing.
>>>>>>>
>>>>>>> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
>>>>>>
>>>>>> @Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?
>>>>>
>>>>> All the other interfaces have size_t as the type for "nb". It is kind
>>>>> of weird as a __u32 would have made more sense, but cannot actually
>>>>> remember why I chose a size_t two years ago. But for consistency with
>>>>> the other interfaces, let us keep it a size_t for now. I will do some
>>>>> research around the reason.
>>>>
>>>> It's actually a bit of a mix currently which is what got me confused:
>>>>
>>>> static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
>>>> static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
>>>> static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod *prod, size_t nb, __u32 *idx)
>>>> static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
>>>> static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, size_t nb, __u32 *idx)
>>>> static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>>>>
>>>> (I can take it in as-is, but would be nice to clean it up a bit to avoid confusion.)
>>>
>>> Hmm, that is confusing indeed. Well, the best choice would be __u32
>>> everywhere since the ring pointers themselves are __u32. But I am
>>> somewhat afraid of changing an API. Can we guarantee that a change
>>> from size_t to __u32 will not break some user's compilation? Another
>>> option would be to clean this up next year when we will very likely
>>> produce a 1.0 version of this API and at that point we can change some
>>> things. What do you think would be the best approach?
>>
>> Given they're all inlines, imho, risk should be fairly low to switch all to __u32.
>> I would probably go and verify first with DPDK as main user of the lib and/or write
>> some test cases to see if compiler spills any new warnings and the like, but if not
>> the case then we should do it for bpf-next so this has plenty of exposure in the
>> meantime. Any nb large than u32 max is a bug in any case.
> 
> Sounds good. Will do and get back to you.

Great, thanks, I took in the current patch to bpf-next in that case and the rest can
be followed-up as discussed.

Thanks,
Daniel