On Fri, Jan 3, 2025 at 11:59 AM Guillaume Nault <gnault@xxxxxxxxxx> wrote: > > On Fri, Jan 03, 2025 at 10:35:55AM -0500, Xin Long wrote: > > On Thu, Jan 2, 2025 at 11:34 AM Guillaume Nault <gnault@xxxxxxxxxx> wrote: > > > > > > Define inet_sk_dscp() to get a dscp_t value from struct inet_sock, so > > > that sctp_v4_get_dst() can easily set ->flowi4_tos from a dscp_t > > > variable. For the SCTP_DSCP_SET_MASK case, we can just use > > > inet_dsfield_to_dscp() to get a dscp_t value. > > > > > > Then, when converting ->flowi4_tos from __u8 to dscp_t, we'll just have > > > to drop the inet_dscp_to_dsfield() conversion function. > > With inet_dsfield_to_dscp() && inet_dsfield_to_dscp(), the logic > > looks like: tos(dsfield) -> dscp_t -> tos(dsfield) > > It's a bit confusing, but it has been doing that all over routing places. > > The objective is to have DSCP values stored in dscp_t variables in the > kernel and keep __u8 values in user space APIs and packet headers. In > practice this means using inet_dscp_to_dsfield() and > inet_dsfield_to_dscp() at boundaries with user space or networking. > > However, since core kernel functions and structures are getting updated > incrementally, some inet_dscp_to_dsfield() and inet_dsfield_to_dscp() > conversions are temporarily needed between already converted and not yet > converted parts of the stack. > > > In sctp_v4_xmit(), there's the similar tos/dscp thing, although it's not > > for fl4.flowi4_tos. > > The sctp_v4_xmit() case is special because its dscp variable, despite > its name, doesn't only carry a DSCP value, but also ECN bits. > Converting it to a dscp_t variable would lose the ECN information. > > To be more precise, this is only the case if the SCTP_DSCP_SET_MASK > flag is not set. That is, when the "dscp" variable is set using > inet->tos. Since inet->tos contains both DSCP and ECN bits, this allows > the socket owner to manage ECN. I don't know if that's intented by the > SCTP code. If that isn't, and the ECN bits aren't supposed to be taken > into account here, then I'm happy to send a patch to convert > sctp_v4_xmit() to dscp_t too.
