On vr, 12 jun 2020 12:03:20 +0200, Oleksij Rempel wrote: > Hello all, > > We have following issues reported on can-utils: > https://github.com/linux-can/can-utils/issues/217 > =============================================================================== > This is a follow-up of the issue #159 . > > When testing the priorities, I noticed, that for the priorities 0 and 1, > the message occurs, that setting the priority is not permitted: > > ./testj1939 -B -s -p3 vcan0:0x80 :,0x0200 > > Works ok. > > ./testj1939 -B -s -p1 vcan0:0x80 :,0x0200 > testj1939: set priority 1: Operation not permitted > > ./testj1939 -B -s -p0 vcan0:0x80 :,0x0200 > testj1939: set priority 0: Operation not permitted > > I am not aware that the priorities 0 & 1 are not permitted. > > > Originally posted by @marckleinebudde in #159 (comment): > > Priorities 0 and 1 are only permitted for root or users with > > capable(CAP_NET_ADMIN), see: > > > https://elixir.bootlin.com/linux/latest/source/net/can/j1939/socket.c#L705 > > > I think this limit is arbitrary and we can discuss if > > this makes sense at all or add this to the > > documentation. If I remember well, there is a similar restriction for ethernet or IP priorities. It's true that this limit is arbritrary. It's based on me never having seen intended prio 0 or 1 messages on a bus, but only as a result of 'we forgot to set the priority'. The goal is to avoid people using 0 as a default without further attention. I think that this could be replaced by some kind of setsockopt call, that sets the highest allowed priority, without ever requiring root. The initial default would then be 2 (or any other value, but 2 seems feasible to me). Kurt
