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Date: Wed, 10 Nov 2010 15:14:47 +0100 From: Kay Sievers <kay.sievers@...y.org> To: Ingo Molnar <mingo@...e.hu> Cc: Peter Zijlstra <peterz@...radead.org>, Greg KH <gregkh@...e.de>, LKML <linux-kernel@...r.kernel.org>, Lin Ming <ming.m.lin@...el.com>, Stephane Eranian <eranian@...gle.com>, "robert.richter" <robert.richter@....com>, Corey Ashford <cjashfor@...ux.vnet.ibm.com>, fweisbec <fweisbec@...il.com>, paulus <paulus@...ba.org>, "H. Peter Anvin" <hpa@...or.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Arnaldo Carvalho de Melo <acme@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: sysfs: Add an 'events' class. (was: Re: [RFC][PATCH] perf: sysfs type id) On Wed, Nov 10, 2010 at 14:36, Ingo Molnar <mingo@...e.hu> wrote: > * Peter Zijlstra <peterz@...radead.org> wrote: > >> On Tue, 2010-11-09 at 14:13 -0800, Greg KH wrote: >> >> > You missed the embedded track at Plumbers where we talked about never >> > adding another class to the kernel. Please use bus_id instead for this. >> >> I did, it was early and I wasn't aware this all comes under the heading >> of embedded. >> >> Anyway, anybody got a good example of bus_type I can 'borrow' ? >> >> Also, it would be really nice if you (plural) could make this subsystem thing >> happen, calling tihngs a bus that aren't a bus just makes me upset ;-) > > Same here - calling events a 'bus' is like totally brain-dead IMHO. It implies > something hardware, while many events are not related to any hardware component but > are pure software abstractions: such as context-switches, or syscall entries, or VM > events. Please use a bus, regardless of the name, class is dead and you will need stuff tha can only happen at bus. We'll fix the name later. > So i'd rather have 'events' or 'event_source' as a 'class' temporarily, than have it > as a 'bus' temporarily - and we get the real fix whenever the sysfs unification > happens. Nope, that can not work. > I also have a question about this future plan mentioned in > Documentation/sysfs-rules.txt: > > - Hierarchy in a single device tree > There is only one valid place in sysfs where hierarchy can be examined > and this is below: /sys/devices. > It is planned that all device directories will end up in the tree > below this directory. > > So did i get it right, sysfs is going to convert from a VFS hiearchy/enumeration to > a flat enumeration of entities, all listed in /dev/devices/? I guess you mean /sys. No, /sys/devices/ is and stays as a hierarchy and will not be flat. > Why is that done? I think it's quite nice that the actual topology is represented > right now via the sysfs VFS structure - so that we have things like: > > /sys/devices/system/ioapic/ioapic0/ That does not change at all. > Where there's is a proper hierarchy showing that we have a 'system', which has an > 'ioapic', which has an ioapic numbered '0'. That entity could then grow 'events' and > have: > > /sys/devices/system/ioapic/ioapic0/events/ > > And could show various IO-APIC events, such as (future, possible events): > > /sys/devices/system/ioapic/ioapic0/events/irq/ > /sys/devices/system/ioapic/ioapic0/events/register-read/ > /sys/devices/system/ioapic/ioapic0/events/register-write/ > /sys/devices/system/ioapic/ioapic0/events/affinity/ > [...] > > So is the plan to get rid of such rich hiearchies and just use a flat store of > everything in /sys/devices/? No. Where do you get that idea from? > My hope would be to _increase_ the depth of sysfs in the future, to express every > meaningful hiearchy that exists in the system (be that hw hierarchy or some sw > abstraction hierarchy). But maybe i got it all wrong so please advise. Yeah, seems all wrong. :) /sys/device is the hierarchy (ans will stay as it is), /sys/class,bus (later /sys/subsystem/) is the flat list of devices per subsystem (to find all devices of a specific subsystem). The list _points_ to devices in /sys/devices, it does never contain any devices. You might want re-read the last mail in this thread, where I explained the difference between hierarchy and classification in more details. Kay -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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