On Wed, Jan 15, 2020 at 05:38:13PM +0000, Chris Wilson wrote: > Quoting Sean Paul (2020-01-15 14:21:18) > > On Wed, Jan 15, 2020 at 02:01:19PM +0000, Chris Wilson wrote: > > > Quoting Sean Paul (2020-01-15 13:41:58) > > > > On Wed, Jan 15, 2020 at 10:36:36AM +0000, Chris Wilson wrote: > > > > > Quoting Sean Paul (2020-01-14 17:21:43) > > > > > > From: Sean Paul <seanpaul@xxxxxxxxxxxx> > > > > > > > > > > > > This patch uses a ring_buffer to keep a "flight recorder" (name credit Weston) > > > > > > of DRM logs for a specified set of debug categories. The user writes a > > > > > > bitmask of debug categories to the "trace_mask" node and can read log > > > > > > messages from the "trace" node. > > > > > > > > > > > > These nodes currently exist in debugfs under the dri directory. I > > > > > > intended on exposing all of this through tracefs originally, but the > > > > > > tracefs entry points are not exposed, so there's no way to create > > > > > > tracefs files from drivers at the moment. I think it would be a > > > > > > worthwhile endeavour, but one requiring more time and conversation to > > > > > > ensure the drm traces fit somewhere sensible. > > > > > > > > > > Fwiw, I have a need for client orientated debug message store, with > > > > > the primary purpose of figuring out -EINVAL. We need per-client so we can > > > > > put sensitive information about the potentially buggy client behaviour, > > > > > and of course it needs to be accessible by the non-privileged client. > > > > > > > > > > On the execution side, it's easy to keep track of the client so we could > > > > > trace execution flow per client, within reason. And we could do > > > > > similarly for kms clients. > > > > > > > > Could you build such a thing with drm_trace underpinning it, just put the > > > > pertinent information in the message? > > > > > > Not as is. The global has to go, and there's no use for debugfs. So we > > > are just left with a sprintf() around a ring_buffer. I am left in the > > > same position as just wanting to generalise tracek to take the ringbuffer > > > as a parameter. > > > > > > > Ah, I think I see what you're getting at now. I think it would be reasonable to > > split out a drm_trace_buffer from the current code for this purpose. We could > > have an interface like: > > > > struct drm_trace_buffer *drm_trace_buffer_init(unsigned int num_pages); > > int drm_trace_buffer_resize(struct drm_trace_buffer *buf, unsigned int num_pages); > > int drm_trace_buffer_printf(struct drm_trace_buffer *buf, const char *format, ...); > > int drm_trace_buffer_output(struct seq_file *seq); > > void drm_trace_buffer_cleanup(struct drm_trace_buffer *buf); > > > > Then to Joonas' point, we could have drm_trace_log which uses this interface to > > mirror the logs with a debugfs interface. > > > > Would that work for your purpose? > > The seq_file doesn't marry with the anticipated uAPI, I'll probably need > a raw file_ops (thinking along the lines of return an fd to userspace, > that is read ala /dev/kmsg). Agree, that should have been struct file_operations *drm_trace_buffer_file_ops(struct drm_trace_buffer *buf); or something like that.. > > I would be tempted to drop the drm_ and put it straight in lib/ I think if we wanted to share this more broadly, we'd probably look at adding it in kernel/trace/ and enabling subsystems to add their own traces to tracefs. Sean > -Chris -- Sean Paul, Software Engineer, Google / Chromium OS
