On (01/18/18 08:53), Eric Dumazet wrote: > > The thing is : MSG_PEEK 'support' will also need SO_PEEK_OFF support.
sure, I'll drop the MSG_PEEK idea (which I wasnt very thrilled about anyway) > So lets properly design things, and not re-use legacy stuff that is > proven to be not multi-thread ready and too complex. > > If you want to design a new channel of communication, do it, and > maintain it. My instinct is to go with the fixed size ancillary data- which itself allows 2 options: 1. cmsg_data has a sock_extended_err preamble with ee_origin = SO_EE_ORIGIN_ZEROCOPY_COOKIE (or similar), and the ee_data is an array of 32 bit cookies (can pack at most 8 32-bit cookies, if we want to pack this into an skb->cb) Using the sock_extended_err as preamble will allow this to be usable by existing tcp zcopy applications (they can use the ee_origin to find out if this a batch of cookies or the existing hi/lo values). 2. If we have the option of passing completion-notification up as ancillary data on the pollin/recvmsg channel itself (instead of MSG_ERRQUEUE) we dont have to try to retain "backward compat" to the SO_EE_ORIGIN_ZEROCOPY API: we can just use a completely new data struct for the notification and potentially pack more cookies into 48 bytes (RDS could be the first guinea pig for this- doesnt even have to be done across all protocol families on day-1). I think the shmem channel suggestion would be an optional optimization that can be added later- it may not even be necessary, since most applications will likely be sending *and* receiving data, so passing up cookies with recvmsg should be "good enough" to save syscall overhead for the common case. I can work #2, if there are no objections to it. --Sowmini
