January 2013 - kernelnewbies@kernelnewbies.org

What is asmlinkage ?
by Rahul Bedarkar Jan. 11, 2013

Jan. 11, 2013

Hi, I was searching for asmlinkage and found that it is already explained at http://kernelnewbies.org/FAQ/asmlinkage But I didn't get this. Can someone tell me about it in brief ? Thanks, Rahul

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internel implemention of file operation
by horseriver Jan. 11, 2013

Jan. 11, 2013

hi: when one file is opened , does its data be put into memory ? and all operation on this file will be implemented by operation on its mapping memory area ? thanks!

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why are scheduling domains used in multiprocessor systems
by Bond Jan. 11, 2013

Jan. 11, 2013

Hi, please see this question http://stackoverflow.com/questions/14229793/what-does-struct-sched-domain-s… I checked following http://lwn.net/Articles/169277/ and following http://www.kernel.org/doc/Documentation/scheduler/sched-domains.txt the first line of kernel.org doc says ............. Each CPU has a "base" scheduling domain (struct sched_domain).............. and second para says " each scheduling domain spans a number of CPUs (stored in the ->span field)." third para says " Each scheduling domain must have one or more CPU groups.................. The intersection of cpumasks from any two of these groups MUST be the empty set." then some where in doc it says "Balancing within a sched domain occurs between groups. That is, each group is treated as one entity." the doc in details talks about the implementation of scheduling domains and mentions that CPUs should belong to one of the scheduling domain in a way that cpumasks intersection should be an empty set The answer of the question that I want to know is why is a scheduling domain actually needed?

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Kernelnewbies Digest, Vol 26, Issue 28
by Ganesh B Jan. 11, 2013

Jan. 11, 2013

Hello, Building a install-able build for linux Kernel, that is it. I have done these: $ make help $ make ARCH=x86 defconfig $ make ARCH=x86 $ make ARCH=x86 module_install gave error nothing to make $ make ARCH=x86 install gave error lilo needs to to be installed. The kernel is built (for all processor types along with multiprocessor support as well), vmlinux.iso and bzimage.iso is there, the libraries are built, modules need to be configured though with grub/ lilo. Will get Lilo installed or a grub creator (what do I use for this?). /boot, /kernel, /library, /.... are there. I do not have /bin, /usr, /etc folders in this. Am I missing something or will that be built during the process. Can someone help me with the steps and syntax's just ahead step by step (like above) further to make a Installer CD and workable boot to be written to a system? The system does not boot with the above, even with a complete copy paste to USB or to a CD. i will take care of complexities myself, just mention any dont's or do's for configuration that is all, I will need help with. TnR, Ganesh

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RE: Kernel-space flirting with user-space
by Rajat Sharma Jan. 11, 2013

Jan. 11, 2013

If you do not have much dependency to be in kernel mode, you can implement, or atleast initially, a user mode filesystem using fuse. ------------------------------ From: Simon Sent: 11-01-2013 02:45 To: kernelnewbies(a)kernelnewbies.org Subject: Kernel-space flirting with user-space Hi there, I'm rather new to kernel development, but I am somewhat experienced with Linux, kernel compilation, etc. I'm just passed writing a helloworld module, dummy filesystem (ramfs wrapper) and proc entry. I would like to know how communication between kernel & user-space is done (the standard) for a high number of tiny and large messages going in both directions (large messages would need to be transfered incrementally, in chunks, can be sequential or random access). I plan on developping a network filesystem. I would appreciate if someone could clarify where I'm wrong and confirm where I'm right, and ideally suggest some vocabulary, source files to lookup, online docs or even books. The minimum you can give will be most appreciated! =) Firstly, I was wondering if it would be possible to implement the filesystem entirely as a kernel module. I would need TCP/UDP sockets. I think this is really not the recommended approach, but an advantage I see is it could be used to mount the root filesystem before calling init (that would be before user-space exists, right?). On the other hand, separating the work to have a program/daemon in user-space do the communication and processing would allow me to write that part in C++ (which I personally prefer). Secondly, I wonder how I can "bind" a user-space program/daemon with the kernel-space of the module. Using procfs: It seems technically possible to achieve my goal with it, but I feel this would not be the standard approach. I would rather keep it for live config & live status reporting. Using sysfs: I've read too much misleading information that I'm not sure anymore what it's for or even if it's still used or deprecated! Can someone clarify? It looks technically identical to procfs, but it's mission is a different one, correct? Using pipes: This may be a good way, but again, I'm not sure if it's the standard way. Using IPC: As far as I understand, IPC would be the way if we'd be talking of two threads within the same process, or at least within kernel-space. Though I am likely to be wrong. Using a char device: It seems technically possible as well, but it may be difficult to deal with if I ever have more than one user-space process. Using a block device: My file system works with files and their metadata, but not with blocks, so this is not suitable. Though it might be a nice experiment to build a network block device containing an ext2 filesystem (which I think would be similar to iSCSI). Using net interface: Not applicable. And an experiment to try to make it applicable doesn't even seem remotely fun. ;) I've seen the functions copy_to/from_user() or something like that, but I haven't seen the user-space counter-part of these. I think this may actually be the best approach by far, but I really lack info/docs to go that way. The truly best way might be to use shared memory to avoid copying data internally, but I haven't looked into that much yet. Finally, is it possible/correct/standard to do something similar to the following for the local kernel & user-space communication? (I haven't reviewed the syntax, so take it as some kind of pseudo-code!) struct foo {...} outgoingFoo; // foo contains no pointers, so it is of a fixed size always. fwrite(&outgoingFoo, 1, sizeof(outgoingFoo), output); [...then on the other end...] if(sizeof(fread( buffer, 1, buffer_size, input); struct foo * incomingFoo = (struct foo *) buffer; Regards, Simon

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where is the build rules for drivers/* ?
by horseriver Jan. 10, 2013

Jan. 10, 2013

hi: when building kernel , kbuild will work into every subdirs . for example: drivers/acpi directory ,there is a makefile , which construct all object files ,but where is the building rules for these file? how kbuild build them out ? Is script/makefile.build doing this work? thanks!

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Cross Compiling a different architechture
by Ganesh B Jan. 10, 2013

Jan. 10, 2013

Hello, I am receiving a configuration and CC1 Errors when cross compiling ARM64 machine from a i386 version. Any help on correct cross compiling a architechture from a different machine. A weblink is also fine. Been trying the docs and some scripts did not work. Is there a method to compile all architectures at the same to save time? I have not been able to do that. TnR, Ganesh

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how to flush stdin buffer in linux
by Niroj Pokhrel Jan. 9, 2013

Jan. 9, 2013

Hi all, I tried to use fflush(stdin) in gcc as I used to in other compilers. But It didn't clear my buffer so I am wondering how can I clear the stdin buffer in GCC. I tried using lseek but got -EPIPE (as tty devices doesn't support lseek operation). Thanx in advance.

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Linux Kernel Map
by Peter Teoh Jan. 9, 2013

Jan. 9, 2013

http://www.makelinux.net/kernel_map/ -- Regards, Peter Teoh

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Re: Kernelnewbies Digest, Vol 26, Issue 24
by Ganesh B Jan. 9, 2013

Jan. 9, 2013

Peter, This was the best. I was struggling to find this. Thank you. TnR, Ganesh ________________________________ From: "kernelnewbies-request(a)kernelnewbies.org" <kernelnewbies-request(a)kernelnewbies.org> To: kernelnewbies(a)kernelnewbies.org Sent: Wednesday, January 9, 2013 5:00 PM Subject: Kernelnewbies Digest, Vol 26, Issue 24 Send Kernelnewbies mailing list submissions to kernelnewbies(a)kernelnewbies.org To subscribe or unsubscribe via the World Wide Web, visit http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies or, via email, send a message with subject or body 'help' to kernelnewbies-request(a)kernelnewbies.org You can reach the person managing the list at kernelnewbies-owner(a)kernelnewbies.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Kernelnewbies digest..." Today's Topics: 1. Linux Kernel Map (Peter Teoh) 2. Re: /usr/ld Not enough room for program headers (horseriver) ---------------------------------------------------------------------- Message: 1 Date: Wed, 9 Jan 2013 21:25:11 +0800 From: Peter Teoh <htmldeveloper(a)gmail.com> Subject: Linux Kernel Map To: "kernelnewbies(a)kernelnewbies.org" <kernelnewbies(a)kernelnewbies.org> Message-ID: <CAHnt0GVj%3DT-E39DLVcYxBL2O48eJZoTeMQuftkk4dKXZrigMKA(a)mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" http://www.makelinux.net/kernel_map/ -- Regards, Peter Teoh

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