March 2012 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Playing with Network Stack
by james jones March 14, 2012

March 14, 2012

Greetings, I hoping someone here can help point me in the right direction. I had an idea for project, but I lack some of the know how. I was wonder if it might be possible to have a kernel module or an application that can inspect and mangle a packet before it gets routed? I don't want to just sniff the traffic. I want to be able to look at the packet and then hand it back to the network stack for processing. If so is there some reading or example code I could look at? Thanks in advance, -James

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How to avoid kernel Oops 0x81F in function do_alignment() ?
by 卜弋天 March 14, 2012

March 14, 2012

Hi experts: an user application generates a un-alignment data abort, then in function do_alignment, kernel read the instruction from the address where data abort occurs by: fault = __get_user(instr, (u32 *)instrptr); after this sentence, instr is the error instruction that generate data abort. i change this instruction from strict alignment check instruction to not strict alignmentcheck instruction by: instr = instr&030; at last i write this instruction back to ram, and let cpu execute this instruction again: *((u32*)instrptr) = instr; it works on kernel 2.6.35, but on version 3.0, it failed, the last sentence above generates a Oops: [ 58.966552] Unable to handle kernel paging request at virtual address 000084ec [ 58.974029] pgd = db9f4000 [ 58.976806] [000084ec] *pgd=1b9db831, *pte=0ae5f59f, *ppte=0ae5fe7e [ 58.986877] Internal error: Oops: 81f [#1] PREEMPT SMP 1. it seems that kernel 3.0 can not modify user mode program instructions directly even underSVC mode. 2. how can i change the page permisson before write back instruction of user mode application? for example, find out the page tables of current application, find out the pte which representsthe instruction that generate data abort, then modify pte, write back instruction, restore pte, done. how to do these? please advise, thanks very much. Best Regards

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remap_pfn_range doubt
by subin gangadharan March 14, 2012

March 14, 2012

Hi All, I am trying to understand how this remap_pfn_range is implemented. I almost got an idea on the implementation. However one thing is not clear, they always subtract userspace address pfn from the physican pfn (http://lxr.linux.no/#linux+v3.2.11/mm/memory.c#L2278) and then adding it back http://lxr.linux.no/#linux+v3.2.11/mm/memory.c#L2284 and calling the inside function. I don't understand why they are not directly passing it. Is there any specific reason for this. Could you please give some pointers on this? -- With Regards Subin Gangadharan I am not afraid and I am also not afraid of being afraid.

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Error while sending patch using git send-email
by Amit Mehta March 13, 2012

March 13, 2012

Hi All, This is not a Linux Kernel related query but is rather on the infrastructure to manage patches using git. Before asking here, I did some search on Internet and also posted this query in a different Linux forum but no luck so far. Hence thought of asking here as someone might have faced this issue, while using the git send-email feature. I've installed git-core and git-send-email packages on my Ubuntu machine and I'm using git to generate patch. Now I want to send this patch, but while doing so, git returns with following error: "5.7.0 Must issue a STARTTLS command first." Some information regarding my setup: slackjaw@swamp:~/linux-next$ cat /etc/issue Ubuntu 11.10 \n \l slackjaw@swamp:~/linux-next$ cat ~/.gitconfig [user] name = Amit email = <XYZ(a)xyz.com> [sendemail] smtpserver = smtp.googlemail.com git command to send patch: slackjaw@swamp:~/linux-next$ git send-email --to "abc(a)xyz.com" 0001-Adding-debugging-level-for-printk.patch The above command returns with error message as mentioned above, whereas my expectation was that git should ask me to enter my password and then send the mail to the destination mail id. I'm able to send and receive mails when I use thunderbird's default settings (In-fact I 'm sending this mail through Thunderbird) which means that there is no issue with the port number or the authentication method for the outgoing mails. -Amit

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New version of beginner's kernel programming course coming soon
by Robert P. J. Day March 13, 2012

March 13, 2012

Hoping I'm not abusing my good will on this list, but I decided it was well past time to bring my original online kernel programming course for beginners up to date, and rather than update the existing course, I'm doing it as a brand new course (2nd ed) here: http://crashcourse.ca/introduction-linux-kernel-programming-2nd-edition/int… FULL DISCLAIMER in that the *full course* will be for paying subscribers only but, just like the original course, the first several lessons will be publicly available and permanently free of charge, and will walk beginners through how to configure, build and reboot a new kernel, as well as write and load their first kernel module and a few other entertaining features of basic kernel programming. Only the first *technical* lesson is up so far, but at the very least, all of the free material should show up over the next several days. So drop by and, as the free lessons show up, play along on your system. And tell your friends. Everyone's welcome. 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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32-bit linux on 64 bit intel arch.
by Onkar N Mahajan March 13, 2012

March 13, 2012

What type of Paging is used when 32-bit linux runs on 64 bit Intel Architecture? (1) 32-bit Paging (2) PAE Paging (3) IA-32e Paging In other words , What kind of paging is used in what situation ? Regards, Onkar

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Macro explanation
by Vijay Chauhan March 13, 2012

March 13, 2012

Hi, I'm checking the container_of and offsetof macro #define container_of(ptr, type, member) ({ \ const typeof( ((type *)0)->member ) *__mptr = (ptr); (type *)( (char *)__mptr - offsetof(type,member) );}) #define offsetof(TYPE, MEMBER) \ ((size_t) &((TYPE *)0)->MEMBER) I did not understand the first line of both macro. Will it not create the NULL pointer dereference problem? I know it works and read some article but it did not explain this part, so can anyone explain why the NULL pointer error is not coming. Am I missing something? Any C language specification of such example.

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Kernel threads and system usage metric.
by Daniel Hilst March 12, 2012

March 12, 2012

Doubt! The processes that appear in top with brackets are the kernel threads? If so, this threads spend all its time on system mode, right? By the system mode I mean the %sy on top header, since kernel threads hasn't any memory mapped to user space, it can't run on user space at any time, right? So the total of system mode usage is the sum of all processes processing in kernel space, plus the kernel threads processing, right? Thanks in advance! -- Follow the white rabbit!

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Correct Place of calling a driver initialization function.
by KARTHIK SEKURU March 12, 2012

March 12, 2012

Hi, I am new to linux-kernel and am using kernel 3.1.6 and working on arm-SemiHosting(through USB) drivers. We are using SemiHosting to exchange/transfer data from the arm-board to the PC. Board details – Using ARM926e-js processor with 128MB SDRAM., Clock-33Mhz SDRAM Size = 128M CONFIG_PAGE_OFFSET = 0xc0000000 CONFIG_PHYS_OFFSET= 0x80000000 Kernel Lowmem = 32M including 8M for initramfs (starting from 24M to 32M). HighMEM is not configured. Vmalloc_start = end address of LowMem (i.e 0xC200000) VMALLOC_END = Vmalloc_start + 64M = 0xC6000000 The SemiHosting(USB) drivers have read(); write(); seek(); functionalities along with an InitUSB function that initializes the semihosting USB hardware unit on the arm board. We are using kernel ioremap() function for accessing the USB register set, which is remaped to malloc section. Functionality in semihosting init (InitUSB) function – 1. We send header command to hostPC via USB DMA operation by setting few USB registers. USB DMA takes the start address of the header and it’s size and these two params (addr, size) are set into corresponding USB registers. The USB transfer is enabled by setting USB_EN register to appropriate value. 2.After header transfer acknowledgement from hostPC should be received. As acknowledgement , hostPC should set INTC_USB register, we poll for this register and once this is set we are done with the initialisation. I wanted to test if the InitUSB function is working as expected. So I called this function in the start_kernel(after Console_Init()). As this function is just setting few registers and polling for few registers., I io_remaped this register set in the InitUSB function.. But the INTC_USB register that is set by the hostPC as acknowledgement is not getting set and the code is never coming out of the while loop. Now, I wanted to know if the place from where the InitUSB() function is called is the culprit and due to it if I am not receiving acknowledgement from the PC. As mentioned I am calling the Init_USB function in the start_kernel(after Console_Init()). Karthik.

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Inlined functions in network code
by Łukasz Czyż March 11, 2012

March 11, 2012

Hello I implemented stateful IPv6-IPv4 NAT translator which works on top of netfilter. It is fully functional now, I only have a doubt about criterion when to declare function as inline. Should all functions which are used during packet translation (so they may be called very frequently) be inlined? Translator is released under GPLv2 license. You can find more info about it at http://czyzu.pl/xlat.html Lukasz

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