Re: [Qemu-devel] [PATCH v4 09/11] netfilter: add a netbuffer filter

[Jason Wang]

On 08/06/2015 04:19 PM, Yang Hongyang wrote:
>
>
> On 08/06/2015 03:21 PM, Jason Wang wrote:
>>
>>
>> On 08/04/2015 04:30 PM, Yang Hongyang wrote:
>>> This filter is to buffer/release packets, this feature can be used
>>> when using MicroCheckpointing, or other Remus like VM FT solutions, you
>>> can also use it to simulate the network delay.
>>> It has an interval option, if supplied, this filter will release
>>> packets by interval.
>>>
>>> Usage:
>>>   -netdev tap,id=bn0
>>>   -netfilter buffer,id=f0,netdev=bn0,chain=in,interval=1000
>>>
>>> NOTE:
>>>   the scale of interval is microsecond.
>>>
>>> Signed-off-by: Yang Hongyang <address@hidden>
>>> ---
>>> v4: remove bh
>>>      pass the packet to next filter instead of receiver
>>> v3: check packet's sender and sender->peer when flush it
>>> ---
>>>   net/Makefile.objs   |   1 +
>>>   net/filter-buffer.c | 120
>>> ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>   net/filter.c        |   2 +
>>>   net/filters.h       |  17 ++++++++
>>>   qapi-schema.json    |  18 +++++++-
>>>   5 files changed, 157 insertions(+), 1 deletion(-)
>>>   create mode 100644 net/filter-buffer.c
>>>   create mode 100644 net/filters.h
>>>
>>> diff --git a/net/Makefile.objs b/net/Makefile.objs
>>> index 914aec0..5fa2f97 100644
>>> --- a/net/Makefile.objs
>>> +++ b/net/Makefile.objs
>>> @@ -14,3 +14,4 @@ common-obj-$(CONFIG_SLIRP) += slirp.o
>>>   common-obj-$(CONFIG_VDE) += vde.o
>>>   common-obj-$(CONFIG_NETMAP) += netmap.o
>>>   common-obj-y += filter.o
>>> +common-obj-y += filter-buffer.o
>>> diff --git a/net/filter-buffer.c b/net/filter-buffer.c
>>> new file mode 100644
>>> index 0000000..fd467db
>>> --- /dev/null
>>> +++ b/net/filter-buffer.c
>>> @@ -0,0 +1,120 @@
>>> +/*
>>> + * Copyright (c) 2015 FUJITSU LIMITED
>>> + * Author: Yang Hongyang <address@hidden>
>>> + *
>>> + * This work is licensed under the terms of the GNU GPL, version 2 or
>>> + * later.  See the COPYING file in the top-level directory.
>>> + */
>>> +
>>> +#include "net/filter.h"
>>> +#include "net/queue.h"
>>> +#include "filters.h"
>>> +#include "qemu-common.h"
>>> +#include "qemu/timer.h"
>>> +#include "qemu/iov.h"
>>> +
>>> +typedef struct FILTERBUFFERState {
>>> +    NetFilterState nf;
>>> +    NetQueue *incoming_queue;
>>> +    int64_t interval;
>>
>> Can interval be negative?
>
> No.
>
>> If not please uint. And not sure you really
>> need a 64 bit integer, if not, please use uint32_t.
>
> Ok, will use uint32_t instead.
>
>>
>>> +    QEMUTimer release_timer;
>>> +} FILTERBUFFERState;
>>
>> Filter buffer is not abbreviation. So better name it as
>> FilterBufferState.
>
> Ok, thanks.
>
>>
>>> +
>>> +static void packet_send_completed(NetClientState *nc, ssize_t len)
>>> +{
>>> +    return;
>>> +}
>>
>> Why need a dummy sent cb?
>
> Need to work around with queue_append, if there's no sent_cb,
> queue_append
> will simply drop the packet...Even we provide a sent_cb param to
> receive_iov,
> this dummy might still be needed because sent_cb might be null.

Dropping happens only when the number of queued packet exceeds queue
limitation and no sent_cb. Isn't this just what we want? And like we've
discussed, we need track packet->sent_cb so it was not a problem?

>
>>
>>> +
>>> +static void filter_buffer_flush(NetFilterState *nf)
>>> +{
>>> +    FILTERBUFFERState *s = DO_UPCAST(FILTERBUFFERState, nf, nf);
>>> +    NetQueue *queue = s->incoming_queue;
>>> +    NetPacket *packet;
>>> +
>>> +    while (queue && !QTAILQ_EMPTY(&queue->packets)) {
>>> +        packet = QTAILQ_FIRST(&queue->packets);
>>> +        QTAILQ_REMOVE(&queue->packets, packet, entry);
>>> +        queue->nq_count--;
>>> +
>>> +        if (packet->sender && packet->sender->peer) {
>>> +            qemu_netfilter_pass_to_next(nf, packet->sender,
>>> packet->flags,
>>> +                                        packet->data, packet->size);
>>> +        }
>>> +
>>> +        /*
>>> +         * now that we pass the packet to next filter, we don't
>>> care the
>>> +         * reture value here, because the filter layer or other filter
>>> +         * will take care of this packet
>>> +         */
>>> +        g_free(packet);
>>
>> This seems wrong, since packet could be queued into incoming queue.
>> Doing this may cause use after free.
>
> The incoming queue will make a copy of packet data when queued a packet.
> So I think it's ok to free this packet here...because this packet is
> alloced by this filter when calling qemu_net_queue_append_iov.
>

You're right. I see.

>>
>>> +    }
>>> +}
>>> +
>>> +static void filter_buffer_release_timer(void *opaque)
>>> +{
>>> +    FILTERBUFFERState *s = opaque;
>>> +    filter_buffer_flush(&s->nf);
>>> +    timer_mod(&s->release_timer,
>>> +              qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) + s->interval);
>>> +}
>>> +
>>> +/* filter APIs */
>>> +static ssize_t filter_buffer_receive_iov(NetFilterState *nf,
>>> +                                         NetClientState *sender,
>>> +                                         unsigned flags,
>>> +                                         const struct iovec *iov,
>>> +                                         int iovcnt)
>>> +{
>>> +    FILTERBUFFERState *s = DO_UPCAST(FILTERBUFFERState, nf, nf);
>>> +    NetQueue *queue = s->incoming_queue;
>>> +
>>> +    qemu_net_queue_append_iov(queue, sender, flags, iov, iovcnt,
>>> +                              packet_send_completed);
>>> +    return iov_size(iov, iovcnt);
>>
>> So if interval is zero, packet will be blocked forever and memory will
>> be exhausted.
>
> Yes, but this supposed to be used by FT solutions, so it will
> be released periodically. Currently only used with interval makes sense.
>

Then you need terminate the initialization when interval is zero.

[...]