On Fri, 19 Aug 2022 10:54:51 -0700 Jakub Kicinski wrote: > > Ugh, I repressed all those memories ... I don't remember now, I guess > > I'd have to try it. Also it doesn't just apply to normal stuff but also > > multicast, and that can be even trickier. > > No worries, let me try myself. Annoyingly I have this doc on a different > branch than my netlink code, that's why I was being lazy :) Buffer sizing ------------- Netlink sockets are datagram sockets rather than stream sockets, meaning that each message must be received in its entirety by a single recv()/recvmsg() system call. If the buffer provided by the user is too short, the message will be truncated and the ``MSG_TRUNC`` flag set in struct msghdr (struct msghdr is the second argument of the recvmsg() system call, *not* a Netlink header). Upon truncation the remaining part of the message is discarded. Netlink expects that the user buffer will be at least 8kB or a page size of the CPU architecture, whichever is bigger. Particular Netlink families may, however, require a larger buffer. 32kB buffer is recommended for most efficient handling of dumps (larger buffer fits more dumped objects and therefore fewer recvmsg() calls are needed).
