May 2016 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

why is there still so much __KERNEL__ testing in include/uapi/?
by Robert P. J. Day May 28, 2016

May 28, 2016

continuing down this road of exporting kernel headers, under include/uapi/ (and mostly further under linux/), there's still a *ton* of testing of the __KERNEL__ preprocessor check. now, i realize that when one does "make headers_install", all those files are run through "unifdef" to sanitize almost all of that kernel content, so it's not like it hurts, but is there any reason so much of it is still there? wouldn't it be tidier to get rid of it? or is there some rationale for leaving it there? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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exporting kernel headers via the include/uapi directory
by Robert P. J. Day May 27, 2016

May 27, 2016

next question about exporting kernel headers, this one related to the content placed under include/uapi/. is there any rationale for header files to be living under include/uapi/<somedir> if they're not listed in the corresponding Kbuild file for export? for example, in include/uapi/drm, there are 24 header files, but only 21 of them are mentioned in that Kbuild file -- the Kbuild file doesn't mention armada_drm.h, etnaviv_drm.h or omap_drm.h, and i've verified that running "make headers_install" doesn't install those three headers. i'm going to assume those are just forgotten remnants or something, unless there is some actual reason to do that. is there? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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some simple(?) questions about Kbuild and installing kernel headers
by Robert P. J. Day May 27, 2016

May 27, 2016

for various reasons, i'm poring over the grotty details of the installation of kernel headers, so a couple questions before i get any further into the code. first, is there any value to a Kbuild file with no content? for example, here's the entirety of arch/cris/include/arch-v10/arch/Kbuild: # CRISv10 arch that is, one commented-out line, no references to any include files. does such a file have any meaning? or can such files be deleted until such time as they need to contain some content? next, with an example from that same directory, the "page.h" header file: #ifndef _CRIS_ARCH_PAGE_H #define _CRIS_ARCH_PAGE_H #ifdef __KERNEL__ ... snip ... #endif #endif in other words, the *entirety* of the contents of that header file are protected by "__KERNEL__". first, that seems silly given that we know the Kbuild file is empty (but that's admittedly an obscure situation). but even if the Kbuild file *wasn't* empty, there are two sub-cases. first, if the "page.h" header file isn't being exported to user space, there's no need for any use of __KERNEL__ to begin with since it's exclusively a kernel header file. and if it *is* being exported, what ends up being exported is, well, an empty header file, correct? which seems a bit silly, *unless* ... are there cases where certain header files *must* exist in user space just as placeholders, even if they're empty? that would explain it, but it still seems yucky. one last query ... is there any value to an unexported header file containing any __KERNEL__ protection? i'm assuming not; examples of that are probably just leftovers that weren't cleaned up properly. more questions later as i get deeper into the code ... rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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IRC channel for linux-block layer and linux-mmc discussion
by Ritesh Harjani May 27, 2016

May 27, 2016

Guys, Can someone please tell IRC channel & server for discussion on linux-block layer and linux-mmc discussion? Regards Ritesh

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GobiNet USB driver support for Big endian
by Narasimha M May 26, 2016

May 26, 2016

Hi All, We have GobiNet usb driver open source, which is working fine with little endian architecture. Facing issues with Big-Endian architecture. Please help if some one supported for Big_endian. -- Narasimha

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Re: Changing the default scheduler
by Frederic Weisbecker May 26, 2016

May 26, 2016

(Sorry I forgot to Cc kernelnewbies, I fixed the Cc line). On Tue, May 24, 2016 at 11:47:37AM +0000, Renato Utsch wrote: > Hi Frederic, > > Thanks, this was exactly what I was looking for! I was suspecting that all > the processes would inherit the policy of the init process, but I didn't > know where to look at. I'll take a look at this and see what happens. > > By the way, how are the scheduler policies and the schedulers related? > Because the RT scheduler can be used with either SCHED_FIFO or SCHED_RR. > Are some policies linked to particular schedulers? If so, can I introduce > new SCHED_* constants? How should I do that if I want to call > sched_setscheduler() to change the policy to, say, SCHED_MY in an userspace > program? What you refer as "scheduler" is in fact a scheduler class. So we have two different notions here: scheduler policy and scheduler class. _ The scheduler policy is set by the user or the system to tell how to schedule a task. That's in the user interface level. _ The scheduler classes handle the tasks scheduling differently on top of their scheduler policy (driven by the user) or on top of kernel internal needs (idle_sched_class and stop_sched_class). We have 4 of them, from lowest prio to highest: _ idle_sched_class = implement idle tasks. The idle tasks (one per CPU) are set with SCHED_NORMAL but the policy of idle tasks are not even checked. _ fair_sched_class = implement SCHED_NORMAL/SCHED_FAIR and SCHED_IDLE (not to be confused with idle tasks. In fact SCHED_IDLE tasks are normal tasks that execute when there is no SCHED_NORMAL tasks to run) _ rt_sched_class = implement SCHED_RR and SCHED_FIFO _ dl_sched_class = deadline realtime tasks (SCHED_DEADLINE) _ stop_sched_class = stop machine tasks. They don't refer to any policy, the stop machine tasks call sched_set_stop_task() to switch to this class. Their policy are SCHED_NORMAL but it's ignored. That's in the implementation level. When the scheduler needs to choose the next task to run on the CPU, it iterates each class from highest prio to lower: (stop, dl, rt, fair, idle) and calls the ->pick_next_task() callback for each of these classes. The first one that has a task to run will have it on the CPU. This is how class priorities are implemented. So if you want to implement a new policy, the easiest is to create a new scheduler class but you'll need to decide where it fits between the classes prio. Now when people talk about re-implementing the scheduler, they usually mean the way to schedule the SCHED_NORMAL tasks. If that's what you're interested in, I think you rather want to rewrite kernel/sched/fair.c and do your own fair_sched_class implementation. Now kernel/sched/fair.c does a lot more than just implement fair_sched_class so rewriting it the way you like to experiment will be painful due to the links it has all around in the core kernel. Perhaps it's easier to create your own policy, define its prio between idle_sched_class and fair_sched_class then run your task under that policy on a CPU that doesn't have any SCHED_NORMAL tasks. You can also set the init/0 task to your policy but there is no guarantee it will propagate all along recursively to the whole process tree as anything can override a parent back to SCHED_NORMAL at some point. Thanks. > > Em ter, 24 de mai de 2016 às 08:39, Frederic Weisbecker <fweisbec(a)gmail.com> > escreveu: > > > Hi Renato, > > > > What you're talking about is not exactly the scheduler but the scheduler > > policy. Basically the scheduler policy is inherited on fork(). The very > > first task (init/0) is initialized with SCHED_NORMAL and this policy is > > inherited recursively through all subsequent fork() calls as it is the root > > parent task. If you want all tasks in the system to inherit a SCHED_FIFO > > policy, you need to change the policy of init/0. This is probably feasible > > in include/linux/init_task.h (I can't check that right now). Now since > > every task will have a real time policy, some of them may starve others. > > You may observe surprising behaviour, your system could even fail to boot. > > > > Have fun. > > Le 20 mai 2016 01:51, "Renato Utsch" <renatoutsch(a)gmail.com> a écrit : > > > >> Hello, > >> > >> I am a new developer trying to learn how to tinker with the kernel. I > >> searched on the internet but couldn't find much info about this (and > >> couldn't find any info up to date). > >> > >> My question is, how does the kernel decide which is the default scheduler > >> that all processes start with? I can change the scheduler of a process by > >> sched_setscheduler(), but how do I change *all* processes from using the > >> CFS scheduler to, for example, the RR scheduler? > >> > >> Sorry if this is too basic, but I don't know where to search for this. If > >> you guys could point me places where I can learn more about this, I would > >> be grateful. > >> > >> _______________________________________________ > >> Kernelnewbies mailing list > >> Kernelnewbies(a)kernelnewbies.org > >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >> > >>

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Re: USB device debugging
by Greg KH May 26, 2016

May 26, 2016

On Wed, May 25, 2016 at 09:11:59PM +0530, Narasimha M wrote: > I am attaching the raw data in two cases (working - 2.mon.out) and not > working (1.mon.out) files. > > working one is with the device having linux 3.10.20 and not working > one is with linux 2.6.32. Here i have run same traffic in both the > cases. You really are on your own with 2.6.32, sorry. If you have issues with that kernel, please contact the vendor that is forcing you to stick with it, as you are paying them to do this work. If that vendor is yourself, well, sorry, it's all your fault, nothing the community can do with such an obsolete and broken kernel release. good luck! greg k-h

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Identify tasks which mmap'ed file
by W. Michael Petullo May 26, 2016

May 26, 2016

Within the kernel and given a struct file *, is it possible to enumerate the tasks which have mmap/MAP_SHARED'ed the file? I have tried to use find_get_pages/rmap_walk on the file's f_mapping field, but this does not seem to work. I find the mapping's first page with find_get_pages, but rmap_walk does not seem to find any vma's as rmap_walk never calls the callback function I pass in. Thank you, -- Mike :wq

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free(), the size to free?
by Wenda Ni May 25, 2016

May 25, 2016

The prototype is void kfree(const void *). As the input pointer is void *, how does the kernel know the size of memory to be freed? There should be some metadata recorded under the hood, right? Thank you for sharing your thoughts. Cheers, Wenda Ni, Ph.D.

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USB device debugging
by Narasimha M May 25, 2016

May 25, 2016

Hi All, Could you please help in checking receive packet flow from USB driver.

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