On (03/15/16 11:09), Eric Dumazet wrote: > > You said "just as user-space SO_SNDBUF allows ridiculous values > for buffer size.." > > So I understood you believe SOCK_MIN_SNDBUF and/or SOCK_MIN_RCVBUF are > ridiculous ;)
No, no! I was saying that as a clueless user-space app, I can SO_SNDBUF to 1, and happily think that everything is fine (error == 0), when in reality the kernel has helpfully fixed up the value for me.. > I pointed to you the actual code. > > sk->sk_sndbuf = max_t(u32, val * 2, SOCK_MIN_SNDBUF); yes, I'm in the process of changing rds-tcp now (doing sanity tests etc on it, will send out update in a short while) > > > No error is returned. kernel enforces a minimal value. > > #define SOCK_MIN_SNDBUF (TCP_SKB_MIN_TRUESIZE * 2) > #define TCP_SKB_MIN_TRUESIZE (2048 + SKB_DATA_ALIGN(sizeof(struct > sk_buff))) > > -> 2 * (2048 + 256) = 4608 given current sk_buff overhead (that might > change in linux 5.4 ... ) Yes, I've seen the comments somewhere (in sock_setsockopt?) it's a bit unexpectd for someone coming from bsd/solaris because the value returned by getsockopt is quite unpredictable (as you point out, depends on the kernel version among other things). > But again if your sysctl allows to set a value below SOCK_MIN_SNDBUF, > that might be a problem, because stack could have a hidden bug for very > small values of sndbuf/rcvbuf. sure, fixing/testing it as I write this. --Sowmini
