(It seems like the list was dropped in my reply, sorry about that. Re-adding it now.) On Thursday, August 18th, 2022 at 14:06, Michał Winiarski <michal.winiarski@xxxxxxxxx> wrote: > On Thu, Aug 18, 2022 at 07:39:13AM +0000, Simon Ser wrote: > > > Hm, I'm a bit worried about the user-space implications of this… e.g. libdrm > > can check for the major/minor to find out the type of a node. Dropping CONTROL > > from the enum will break that. > > Yeah, but that would only cause problems if there are more than 64 devices in > the system, and the user-space in question is smart enough to support that. > > IIUC libdrm only looks for 16 devices: > https://gitlab.freedesktop.org/mesa/drm/-/blob/main/xf86drm.h#L47 > > I'm not very familiar with mesa codebase, but I think it has something similar: > https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/gallium/auxiliary/pipe-loader/pipe_loader_drm.c#L52 > > I expect other clients to also have something similar (loop over minors, 0-63 > for primary, 128-191 for render). > > So this shouldn't really cause a regression, it's just that "old" userspace > won't be able to use more devices (but it's also not able to use more devices > without this series). Unfortunately I think there are more assumptions all over the place, see e.g. drmGetMinorType: https://gitlab.freedesktop.org/mesa/drm/-/blob/main/xf86drm.c#L986 Also I'm not very found of dropping DRM_NODE_CONTROL from the kernel enum -- this results in DRM_NODE_RENDER=1 in the kernel but DRM_NODE_RENDER=2 in user-space which sounds pretty error-prone. > I could go with 0-63 primary, 64-127 empty, 128-191 render, 192-255 primary, > 256-319 empty, (...) > But it just seems like a waste to burn 1/3 of minors. Could potentially work I guess. > Perhaps it would also be possible to go with: > 0-63 primary, 64-127 empty, 128-191 render, 192-512K continuous range > where we distribute minors first-come first-serve, without any link to type (so > usually we'd get continuous card192, renderD193, and so on) We would need to re-design drmGetMinorType if we go down this path.
