Re: [PATCH v5 4/4] vhost-user: add vhost-user

[Laurent Vivier <lvivier@redhat.com>]

On 16/09/2024 09:00, David Gibson wrote:
>> --- a/tap.c
>> +++ b/tap.c
>> @@ -58,6 +58,7 @@
>>   #include "packet.h"
>>   #include "tap.h"
>>   #include "log.h"
>> +#include "vhost_user.h"
>>   
>>   /* IPv4 (plus ARP) and IPv6 message batches from tap/guest to IP handlers */
>>   static PACKET_POOL_NOINIT(pool_tap4, TAP_MSGS, pkt_buf);
>> @@ -78,16 +79,22 @@ void tap_send_single(const struct ctx *c, const void *data, size_t l2len)
>>   	struct iovec iov[2];
>>   	size_t iovcnt = 0;
>>   
>> -	if (c->mode == MODE_PASST) {
>> +	switch (c->mode) {
>> +	case MODE_PASST:
>>   		iov[iovcnt] = IOV_OF_LVALUE(vnet_len);
>>   		iovcnt++;
>> -	}
>> -
>> -	iov[iovcnt].iov_base = (void *)data;
>> -	iov[iovcnt].iov_len = l2len;
>> -	iovcnt++;
>> +		/* fall through */
>> +	case MODE_PASTA:
>> +		iov[iovcnt].iov_base = (void *)data;
>> +		iov[iovcnt].iov_len = l2len;
>> +		iovcnt++;
>>   
>> -	tap_send_frames(c, iov, iovcnt, 1);
>> +		tap_send_frames(c, iov, iovcnt, 1);
>> +		break;
>> +	case MODE_VU:
>> +		vu_send(c->vdev, data, l2len);
> I'm a bit uneasy re-introducing a parallel send function for the slow
> path, rather than using a common tap_send_frames() interface.  Any
> chance you can unify those sensibly?  Bearing in mind that this_is_
> the slow path, so if you have to copy a bunch of stuff, that's ok.

I tried but it's over complicated to take in input an iovec array and to use another iovec 
array (provided by the guest) to send data. It's easier to have a buffer and to copy it to 
the iovec array buffers of the guest. Moreover we don't need to have a 
tap_send_frames_vu() (see vu_handle_tx()), so we will introduce it to always send an iovec 
array with only one entry.

Thanks,
Laurent