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

PCI system start point
by J.Hwan Kim April 9, 2012

April 9, 2012

Hi, everyone In kernel source 2.6.25, the start point of PCIe system was pci_init(). Now in version 3.x.x, the function name of pci_init() disappeared. Where is the start point of pci system in current version? Thanks in advance. Best Regards, J.Hwan Kim

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Driver for UPS
by Peter Senna Tschudin April 8, 2012

April 8, 2012

Dear list, I want to write a driver for my UPS. My goal is to plug the USB cable, and have the system to recognize the device as battery + AC power supply. The effect I'm looking for is GNOME showing an icon with battery load, power source state and time remaining to full and empty battery. Some UPS from APC behave exactly like this. But it is not clear how it is done. I made a C program that talks to the UPS but I need some guidance from here. How should this be implemented? Should I do a Kernel module or deal with it on userland? I found nut (http://www.networkupstools.org/) and apcupsd (http://www.apcupsd.org/) that are not what I'm looking for. Any references about APC UPS + Kernel are welcome. Thanks! Peter -- Peter Senna Tschudin peter.senna(a)gmail.com gpg id: 48274C36

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Sending off kernel patches
by adhirramjiawan0＠gmail.com April 7, 2012

April 7, 2012

Hi all! I'm new to kernel development and I have just started learning how to create linux kernel patches. I would like to know how the 'signing off' and 'acknowledgment' processes work? I'm assuming that I as the patch author I need to sign off, but who do I send the file to so that it can be acknowledged? Do I need to find an individual who's actively involved in kernel development? Thanks in advance! Adhir Sent via my BlackBerry from Vodacom - let your email find you!

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Looking for small Confirmation about skb_pull & NF_ACCEPT !!!
by Kesava Srinivas April 6, 2012

April 6, 2012

HI Friends, Looking for a Confirmation on my analysis. Once after Capturing the Socket Buffer in PRE_ROUTING Hook; Manipulated the Socket Buffer by using the "skb_pull" Kernel Function. Using skb_pull; stripped 28 bytes (IP+UDP) which are the Part of outer UDP/IP Header. Now; My intention was to route the skb based on the Inner IP Header which is sitting after stripping 28 bytes. At the END; returned NF_ACCEPT. Even though; skb_pull worked Fine., Kernel's Stack is still looking in to Outer Header only for Routing the Packet.I expected ;Kernel will look the Inner Header (As data Pointer was incremented by 28 bytes via skb_pull) and Take decision based on the Inner one. But; that didn't happened. It looks to me like; we need to always use NF_STOLEN & should write our own code to route based on the INNER HEADER. Was my conclusion correct ?? -Thanks in Advance, VKS

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Some questions about high memory
by loody April 6, 2012

April 6, 2012

hi all: I am trying to write a driver for my block device which dma support high memory copying. I have register my device as "blk_bounce_any". But my driver cannot see block layer pass high memory to me so far. Is there any user/kernel test program which will purposely send high memory for driver to use? or is there any flag when opening a file in user mode that will use high memory? -- Thanks for your help in advance,

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CPU Load Balancer / Scheduler / CFS
by Robert W April 6, 2012

April 6, 2012

I'm seeing some bizarre differences between two servers (one running 2.6.32 and the other 2.6.18) with how processes are spread across CPUs. I created a simple test client: https://gist.github.com/2306761 which forks 4 times to create processes which just consume cpu. On 2.6.18, the processes are distributed across CPUs as expected (all 4 processes are consuming 100%). But on 2.6.32, the distribution varies. Sometimes it's (100%, 33%, 33%, 33%), other times it's (100%, 100%, 50%, 50%), etc.. while all the other CPUs sit completely idle.. Both servers have many cores (more than 4). Both servers each have 2 physical processors, and are hyper-threaded. I've done many other similar tests (tried running the "stress" program with different parameters and I also got bizarre results. It basically looks like the CPU Load Balancer never moves a process to a different CPU under any circumstances). I haven't set anything regarding cpusets / etc. so it should all be default behavior. Also, if I manually move the processes to other cpus (using taskset) then I can get them to all run at 100%. What could be going on here?

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reboot.c and X86-64 architectures
by Miles Fidelman April 5, 2012

April 5, 2012

Hello Folks, Perhaps someone here can help me understand the behavior of the kernel reboot code. I've recently migrated from running a 32bit kernel to a 64bit one (specifically Debian Lenny 32bit environment to 2.6.32-5-xen-amd64 on top of xen-4.0-amd64 hypervisor build). This is a somewhat older, and apparently quirky, hardware box. I've found that the only way to reboot it, short of power cycling, is jumping through the bios - using the "reboot=bios" kernel option at boot time works just fine for an X86_32 kernel. But... this doesn't work with the 64bit kernel. Pouring through both the documentation and the code for arch/x86/kernel/reboot.c yields the very specific admonition (in comments describing command-line kernel options), that reboot=bios (Reboot by jumping through the BIOS) only applies to X86_32 - and the case statements in the code seem to align with the comment. None of the other available command line options seem to work with my hardware, which leads to two questions: 1. What's the logic behind this? Why not enable a bios reboot for 64bit kernels? Anybody know the history? 2. Anybody know a workaround, short of patching and compiling a custom kernel? Are there other paths through the reboot code that can invoke a bios reboot? (Note: None of the available command line options seem to work on this particular box/bios combination, and kexec-reboot is not available for this combination of kernel and hypervisor). Thank you very much, Miles Fidelman -- In theory, there is no difference between theory and practice. In practice, there is. .... Yogi Berra

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wrapfs sources
by V.Ravikumar April 5, 2012

April 5, 2012

Hi all, Could some body let me know wrapfs sources which is compatible to Linux 2.6.18 kernel sources. I tried to get sources using google search , but all are compatible with latest kernel sources. Thanks & Regards, Ravi

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freeing locks acquired by kernel thread?
by Asim April 4, 2012

April 4, 2012

Hi, I have a driver thread that I kill using do_exit(SIGKILL) upon exception. Unfortunately, I do not see it releasing all locks when it exits and I get a lockdep trace. The exit_sem() code does not seem to free my mutexes. I was wondering if there is way I would make sure I have release all locks before I issue do_exit. I tried to walk the locks in the current thread using this piece of code I've written: struct task_struct *curr = get_current(); int i, depth = curr->lockdep_depth; for (i = 0; i < depth; i++) { printk("\nLock: #%d:\n ", i); printk("[<%p>] %pS\n", (void *) (curr->held_locks + i)->acquire_ip, (void *) (curr->held_locks + i)->acquire_ip); lock_release((curr->held_locks + i)->instance, 1, (curr->held_locks + i)->acquire_ip); } I am able to print the lock correctly (address and IP). But I get "[ BUG: bad unlock balance detected! ]" and "but there are no more locks to release!". And then when I call do_exit, I get unreleased locks message for the same locks. This makes my module unusable, atleast the codepaths where these locks lie (both within and outside my kernel(say locks in sysfs)). If anyone has had success in clearing all locks of a thread upon exit, or has a pointer to such an existing code in kernel it would be useful. Thanks, Asim

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Req help - Panic in VFS mount(Cramfs)
by KARTHIK SEKURU April 4, 2012

April 4, 2012

Hi, I'm doing kernel porting to arm926 based FPGA board, with very minimal setup. Only UART and timer devices are available as part of FPGA. Board details – Using ARM926e-js processor with 128MB SDRAM., Clock-33Mhz SDRAM Size = 128M CONFIG_PAGE_OFFSET = 0xc0000000 CONFIG_PHYS_OFFSET= 0x80000000 Loading the cramfs at 0x82000000 Start address for kernel is 0x80008000 Commandline(atags address) is 0x80000100 Kernel Lowmem = 32M HighMEM is not configured. Vmalloc_start = 0xC40000000 VMALLOC_END = Vmalloc_start + 64M = 0xC8000000 After mounting the CRAMFS filesystem, we are expecting a login prompt. But we are getting kernel panic message as shown below. Please help me in fix the issue. Kindly let me know if further information is needed. *Console message:* VFS: Mounted root (cramfs filesystem) readonly on device 1:0. Freeing init memory: 76K Error -3 while decompressing! c018b094(3087)->c016f000(4096) Error -5 while decompressing! c018bca3(3740)->c0170000(4096) Error -5 while decompressing! c018cb3f(3116)->c0171000(4096) Error -5 while decompressing! c018e76b(5370)->c0172000(4096) Error -3 while decompressing! c018b094(3087)->c016f000(4096) Failed to execute /linuxrc. Attempting defaults... Error -3 while decompressing! c018e8d8(3946)->c0173000(4096) Error -5 while decompressing! c018f842(4930)->c0174000(4096) Error -5 while decompressing! c0190b84(4854)->c0175000(4096) Error -3 while decompressing! c018e8d8(3946)->c0173000(4096) Error -3 while decompressing! c018b094(3087)->c016f000(4096) *Panic meaasge:* Kernel panic - not syncing: No init found. Try passing init= option to kernel. See Linux Documentation/init.txt for guidance. Backtrace: [<c000c378>] (dump_backtrace+0x0/0x10c) from [<c000c49c>] (dump_stack+0x18/0x1c) r6:c001afb4 r5:c0183760 r4:c0183780 r3:60000013 [<c000c484>] (dump_stack+0x0/0x1c) from [<c00179d4>] (panic+0x64/0x1b0) [<c0017970>] (panic+0x0/0x1b0) from [<c0008804>] (init_post+0xb0/0xd4) r3:c3824000 r2:c383a100 r1:c0204740 r0:c014595c r7:00000013 [<c0008754>] (init_post+0x0/0xd4) from [<c0163918>] (kernel_init+0xfc/0x12c) [<c016381c>] (kernel_init+0x0/0x12c) from [<c001afb4>] (do_exit+0x0/0x694) Karthik.

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