Re: [RFC v3 3/8] conf: Add context fields, epoll types and the --vhost flag to pasta

["Ammar Yasser" <aerosound161@gmail.com>]

On Mon Aug 10, 2026 at 4:11 AM EEST, David Gibson wrote: 
>> Add the fd_vhost field on the context which will carry the file
>> descriptor of the device and will indicate that the setup was
>> successful. The vq field contains the kick, call and err file
>> descriptors for both queues.
>> 
>> Also add vhost (mark if vhost acceleration was requested) and
>> virtio_features field.
>
> A couple of concerns about the command line interface.   IIUC, once
> this is all ready the difference between vhost-kernel and regular
> tuntap should be neither guest-visible nor user-visible.  So, assuming
> it does perform better, we'll probably want to make it the default.
>
> So, making this explicitly an opt-in probably isn't what we want.
> Maybe --vhost on|off|auto would be a better idea, defaulting to off
> now, but auto (use if available) in future.  "on" would be if the user
> definitely wants vhost, and would rather we exit than fall back if
> it's not available.

The auto option seems like a nice suggestion. will incorporate it in the
next revision

> A more minor concern is that there's the potential confusion between
> this and --vhost-user.  Not immediately sure what we can do about
> this, since that's just reflecting the confusingly similar names of
> the underlying features.

Good point, will try to find a better fitting name

>> @@ -258,11 +263,14 @@ struct ctx {
>>  	int fd_control;
>>  	int fd_repair_listen;
>>  	int fd_repair;
>> +
>> +	int fd_vhost;
>>  	unsigned char our_tap_mac[ETH_ALEN];
>>  	unsigned char guest_mac[ETH_ALEN];
>>  	uint16_t mtu;
>>  
>>  	uint64_t hash_secret[2];
>> +	uint64_t virtio_features;
>>  
>>  	int ifi4;
>>  	struct ip4_ctx ip4;
>> @@ -288,6 +296,12 @@ struct ctx {
>>  	struct udp_ctx udp;
>>  	int no_icmp;
>>  
>> +	struct {
>> +		int kick_fd;
>> +		int call_fd;
>> +		int err_fd;
>> +	} vq[2];
>> +
>>  	int no_dns;
>>  	int no_dns_search;
>>  	int no_dhcp_dns;
>> @@ -300,6 +314,7 @@ struct ctx {
>>  	int splice_only;
>>  	int host_lo_to_ns_lo;
>>  	int freebind;
>> +	int vhost;
>>  	bool chroot_fallback;
>>  
>>  	int low_wmem;
>
> It might be a bit neater to put the new vhost-kernel related fields
> into a substructure, rather than spreading them across struct ctx.  At
> some point it would be nice to make the various tap backends a bit
> more pluggable / independent from each other.  Doing that's obviously
> not in scope for this series, but keeping it's internal data all
> together will at least not make that job harder in the future.

Good suggestion. Will make things more organized for sure

>
>> -- 
>> 2.34.1
>>