February 2013 - kernelnewbies@kernelnewbies.org

kbuild: building external module in separate output directory
by Yann Droneaud Feb. 13, 2013

Feb. 13, 2013

Hi, With kbuild, we can build external modules using: make -C $KERNEL_BUILDDIR M=$PWD But I'm looking for the proper way to not clobber my module source directory with files from the build, eg. I'd like the build to output the files in another directory. I'd like to do: mkdir obj-$ARCH cd obj-$ARCH make -C $KERNEL_BUILDDIR M=$PWD/.. O=$PWD But O= is not supported for external module. It can only be used when building the kernel (and its modules) itself. I have found people explaining that the currently only way is to copy/link the sources inside the object directory. But I find this tasteless and error prone. Do someone know another method or a patch to the kbuild system to improve external module compilation ? Regards. -- Yann Droneaud OPTEYA

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kernel driver vs userspace program
by Simon Feb. 12, 2013

Feb. 12, 2013

Hi guys, I'm building an electrical device which will be controlled by computer. It will have an embedded microcontroller and will use USB to communicate with the PC. I believe this calls automatically for a device driver, correct? And for using the machine from the PC, interacting with it, that calls for a userspace program, correct? I mean, doing things differently, such as all in userspace or all in-kernel, would be bad form, right? My question is in case the machine is used in an industrial context where there is really only one usage and one kind of interaction that follows a pre-determined procedure (therefore totally automated). This could give extremely high priority of execution, I guess. Similar to a factory robot controlled by a computer. Would it make more sense to have everything in kernel space, while the userspace (if any) would only serve the purpose of reporting? To be a lot more general, I find it simple at first glance to understand what goes where between kernel and user space. But despite this, I often find myself in a gray zone (to my perspective) or I find myself trying to "fit" something I feel is the wrong place. I would need to read more on the philosophy of these different processing spaces, about the design behind them and the usage this philosophy prescribes. Anyone know where I could read about this in greater detail? Thanks, Simon

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LPC313x support - how to do it right?
by Zoltan Gyarmati Feb. 12, 2013

Feb. 12, 2013

Hi, in the last days i managed to rework and split up to more or less logical units the patch provided by NXP (see here: http://ics.nxp.com/support/software/lpc313x.bsp.linux/) for the LPC313x platform to work with linux 3.7. Hence the original patch was against 2.6.33, it doesn't have any device tree bindings, and anyway needs a lot of cleanup, but at this point it works. I'm willing to add the LPC313x support to the mainline kernel (well, if the community doesn't advice against:), but i'm not totally sure about the workflow i'm supposed to follow, so here are my first questions (which probably will be followed by others later on): 1. Do i think right that to get it into the mainline, it needs to support device trees? 2. If so (and i think yes), is there any tutorial regarding to the porting old machine support code and drivers to use device trees? (i checked the kernel documentation and some other machine support code, so i have some idea, but there are lot of unclear details of course...) 3. Regarding to the drivers, my biggest concern is the serial driver: the hw is close to the traditional 8250, but the NXP driver uses DMA access to handle it, which results a lot of changes in the drivers/tty/serial/8250/8250.c (see in the linked kernel tree below). What is the best strategy to follow in such a case? Adding this modifications to the original 8250 and define config macros to handle the differences(which will be kinda messy...), or create separated driver code (which will duplicate some code from the original 8250 driver...) The patchset is available in this Gitorious repo: https://gitorious.org/linux-3-7-gnublin/linux-3-7-gnublin/commits/gnublin-s… in the gnublin-support branch. Currently it provides support for the serial port, the i2c bus, usb host and gadget, and mmc. Thx in advance -- br, Zoltan Gyarmati mail: mr.zoltan.gyarmati(a)gmail.com freenode nick: zgyarmati

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MAX limit of file descriptor
by horseriver Feb. 12, 2013

Feb. 12, 2013

hi:) In one process ,what is the max number of opening file descriptor ? Can it be set to infinite ? In network programing ,what is the essential for the maximum of connections dealed per second thanks!

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Use of copy_to_user() and copy_from_user() functions
by पारस Feb. 12, 2013

Feb. 12, 2013

Hi All, To read/write data to user-space from kernel-space we use copy_from_user() and copy_to_user() functions. What is the use of these function? Why kernel can't directly access user address and read/write on to it? Can any one explain why kernel can't directly access the user-space address. Thanks

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[PATCH] bind micmute led to capslock led on thinkpads
by Jason A. Donenfeld Feb. 11, 2013

Feb. 11, 2013

Hi folks, The attached patch binds the capslock light to the micmute light on my Thinkpad. It works really well. But it's definitely the wrong way to be doing things. There are two problems I'd like to solve a better way: 1) How do I find a pointer to the led_device struct for that led, so that I can call brightness_set on it? 2) How do I hook the kbd_set_leds functions without having to patch atkbd.c? I'm more interested in (1) than (2), but insights on either would be welcome. Thanks! Jason

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Re: Kernel code interrupted by Timer
by Gaurav Jain Feb. 11, 2013

Feb. 11, 2013

Well, my bad. I was wrong there. Your example was correct. Even in a multi-kernel like Barrelfish, each core manages only its own share of memory. RAM is explicitly partitioned between cores running on each kernel and any data structures that need to be shared across cores have to be replicated in each of the memory partitions and consistency maintained through IPC. ~Gaurav On Fri, Feb 8, 2013 at 10:29 PM, Gaurav Jain <gjainroorkee(a)gmail.com> wrote: > I guess you misinterpreted me... A multi-kernel like Barrelfish would have > separate kernel images running on different cores, but each of the > core/kernel would be able to address the *entire* physical memory > (including any memory-mapped devices). Hence, the database would still be > addressable/reachable from all cores. Traditional locking mechanisms to > protect the database (like in a single-kernel Linux) would be good here, > too. OR, like in Barrelfish, we could have explicit inter-core > communication messages to implement synchronization/consistency. > > ~ Gaurav > > > On Fri, Feb 8, 2013 at 9:34 PM, Jeff Haran <Jeff.Haran(a)citrix.com> wrote: > >> Well, for instance what we do. We maintain a big database of cell phone >> user IP addresses and other info in a kernel module running on a 24 core >> X86-64 system. All 24 cores can and do access that data. If each core had >> access to only a single partition of memory, then that DB would have to be >> spread across the various partitions and if the one core that could access >> a specific cell phone user’s info was busy while others were idle, access >> to that user’s would be delayed. The application is quite performance >> sensitive so having the ability for all cores to operate on all data makes >> for better performance.**** >> >> ** ** >> >> Jeff**** >> >> ** ** >> >> *From:* Gaurav Jain [mailto:gjainroorkee@gmail.com] >> *Sent:* Friday, February 08, 2013 11:54 AM >> >> *To:* Jeff Haran >> *Subject:* Re: Kernel code interrupted by Timer**** >> >> ** ** >> >> "you can solve problems that can’t be easily solved if all the data is >> partitioned by CPU core."**** >> >> ** ** >> >> Can you please give an example or two of the aforementioned problems? I >> can think of efficient scheduling - a single kernel knowing what >> cores/processors are idle would help make better decisions without the >> overhead of message passing in separate kernels on separate cores.**** >> >> ** ** >> >> ~Gaurav**** >> >> ** ** >> >> On Fri, Feb 8, 2013 at 8:16 PM, Jeff Haran <Jeff.Haran(a)citrix.com> wrote: >> **** >> >> I did not write Linux, so just guessing here. I don’t think the issue is >> so much kernel images as shared access to kernel data. The synchronization >> primitives in the kernel (spin locks, read-write locks, RCU, etc) are there >> to protect data from being corrupted during concurrent access, not code. I >> am not familiar with barrelfish but I think most modern OSes, for instance >> the various BSD derivatives, work like this. I have no recent experience >> with it, but I’d bet Windows does the same thing. If you can run multiple >> cores on the same data safely by providing proper locking, you can solve >> problems that can’t be easily solved if all the data is partitioned by CPU >> core.**** >> >> **** >> >> Getting the locking right though can be a challenge, which is of course >> good for software engineer job security. 8^)**** >> >> **** >> >> Jeff**** >> >> **** >> >> *From:* Gaurav Jain [mailto:gjainroorkee@gmail.com] >> *Sent:* Friday, February 08, 2013 11:03 AM >> *To:* Jeff Haran >> *Subject:* Re: Kernel code interrupted by Timer**** >> >> **** >> >> "On multi-core systems this should be done regardless of whether kernel >> pre-emption is enabled or not"**** >> >> **** >> >> -- Do you know why such a design decision was made - That a single kernel >> image should manage all the cores! I have worked on Barrelfish ( >> http://www.barrelfish.org/) a bit, and it boots a separate kernel on >> each of the cores. To me that appears to be the more intuitive approach. >> What advantages do we get by having a single kernel image on all cores? Is >> the convenience of being in the same address space (the single kernel's) at >> all cores at all times, the only/major reason? **** >> >> **** >> >> ~Gaurav**** >> >> **** >> >> On Fri, Feb 8, 2013 at 7:51 PM, Jeff Haran <Jeff.Haran(a)citrix.com> wrote: >> **** >> >> I think you will find that this is a matter of kernel configuration. If >> kernel pre-emption is enabled at build time, then following the interrupt >> another process could get scheduled and it wouldn’t matter what interrupt >> went off. Typically some sort of explicit locking or RCU is used to protect >> critical sections in cases like this. On multi-core systems this should be >> done regardless of whether kernel pre-emption is enabled or not.**** >> >> **** >> >> Jeff Haran**** >> >> **** >> >> *From:* kernelnewbies-bounces(a)kernelnewbies.org [mailto: >> kernelnewbies-bounces(a)kernelnewbies.org] *On Behalf Of *Gaurav Jain >> *Sent:* Friday, February 08, 2013 9:09 AM >> *To:* Kernel Newbies >> *Subject:* Kernel code interrupted by Timer**** >> >> **** >> >> What happens if the kernel executing in some process context (let's say >> executing a time-consuming syscall) gets interrupted by the Timer - which >> is apparently allowed in 2.6 onwards kernels.**** >> >> **** >> >> My understanding is that once the interrupt handler is done executing, we >> should switch back to where the kernel code was executing. Specifically, >> the interrupt handler for the Timer interrupt should not schedule some >> other task since that might leave kernel data in an inconsistent state - >> kernel didn't finish doing whatever it was doing when interrupted. **** >> >> **** >> >> So, does the Timer interrupt handler include such a policy for the above >> case? **** >> >> **** >> >> -- **** >> >> Gaurav Jain**** >> >> **** >> >> **** >> >> >> >> **** >> >> **** >> >> -- **** >> >> Gaurav Jain**** >> >> Associate Software Engineer**** >> >> VxVM Escalations Team, SAMG**** >> >> Symantec Software India Pvt. Ltd.**** >> >> **** >> >> >> >> **** >> >> ** ** >> >> -- **** >> >> Gaurav Jain**** >> >> Associate Software Engineer**** >> >> VxVM Escalations Team, SAMG**** >> >> Symantec Software India Pvt. Ltd.**** >> >> ** ** >> > > > > -- > Gaurav Jain > Associate Software Engineer > VxVM Escalations Team, SAMG > Symantec Software India Pvt. Ltd. > > > -- Gaurav Jain Associate Software Engineer VxVM Escalations Team, SAMG Symantec Software India Pvt. Ltd.

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Re: error : insmod
by Kristof Provost Feb. 11, 2013

Feb. 11, 2013

On 2013-02-11 16:24:17 (+0530), sunil <sunil.slvphsn(a)gmail.com> wrote: > Have a look at this: > > donno wats happening: > > sunil@ubuntu:~/test/drive$ sudo rmmod helloworld > sunil@ubuntu:~/test/drive$ lsmod|grep hellow* > Binary file helloworld.ko matches > Binary file helloworld.o matches This doesn't actually do what you seem to think it does. You're not passing the 'hellow*' argument to grep. The 'hellow*' is first expaned by your shell, so it probably turns that command line into 'lsmod | grep helloworld.c helloworld.o helloworld.ko'. Try using 'lsmod | grep hellow' instead (i.e. without the *). > sunil@ubuntu:~/test/drive$ modprobe -r helloworld > FATAL: Module helloworld not found. Obviously, because your previous command succeeded. The module is no longer loaded. Regards, Kristof PS: Please don't top-post. PS 2: Please keep the mailing list in cc.

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Re: error : insmod
by Kristof Provost Feb. 11, 2013

Feb. 11, 2013

On 2013-02-11 16:10:38 (+0530), sunil <sunil.slvphsn(a)gmail.com> wrote: > -------------output---------------------------- > sunil@ubuntu:~/test/drive$ sudo insmod ./helloworld.ko > insmod: error inserting './helloworld.ko': -1 File exists > This means you've already loaded the module. Try 'sudo rmmod helloworld' to unload it first. This should generate the 'Goodbye, cruel world' dmesg trace. After that you can load the module again. Regards, Kristof

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error : insmod
by sunil Feb. 11, 2013

Feb. 11, 2013

hi all, while inserting module to the linux kernel, m facing this problem -------------------------------------------ERROR----------------------------------------------------- sunil@ubuntu:~/test/drive$ insmod helloworld.ko insmod: error inserting 'helloworld.ko': -1 Operation not permitted sunil@ubuntu:~/test/drive$ sudo modprobe helloworld FATAL: Module helloworld not found. please help!! thanks & regards Sunil

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