On 2018/12/13 13:59, David Miller wrote: > From: jiangyiwen <jiangyiwen@xxxxxxxxxx> > Date: Thu, 13 Dec 2018 11:11:48 +0800 > >> I hope Host can fill fewer bytes into rx virtqueue, so >> I keep structure virtio_vsock_mrg_rxbuf_hdr one byte >> alignment. > > The question is if this actully matters. > > Do you know? > > If the obejct this is embeeded inside of is at least 2 byte aligned, > you are marking it packed for nothing. > > There are only %100 downsides to using the packed attribute. > > Simply define your datastructures properly, with fixed sized types, > and all padding defined explicitly. > > . > Hi David, Thanks a lot, I need to send number buffers from Host to Guest, so I think we need to keep the structure size the same between host and guest. But after your reminder, I feel my code may exist a serious problem, that in mergeable mode, I send the total structure virtio_vsock_pkt from Host to Guest, however, this structure size may be different under different compilers (Guest and Host are different). Then, Guest may parse the wrong packet length. David, I want to ask if there is such a problem? In addition, why I send total virtio_vsock_pkt structure from Host to Guest? - In order to avoid to allocate virtio_vsock_pkt memory when receiving packets, in case of insufficient memory, it may have some advantages, and we may keep consistent with old version. Thanks again, Yiwen.
