November 2014 - kernelnewbies@kernelnewbies.org

The kernel memory limit of 64bit system
by J.Hwan Kim Nov. 28, 2014

Nov. 28, 2014

Hi, everyone How much is the kernel memory limit of 64 bit system? As far as I know, int 32 bit system the kernel memory limit is 1GB. Is it also applicable to 64bit system? Thanks in advance Regards, J.Hwan Kim

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Split RAID: Proposal for archival RAID using incremental batch checksum
by Anshuman Aggarwal Nov. 27, 2014

Nov. 27, 2014

I'd a appreciate any help/pointers in implementing the proposal below including the right path to get this into the kernel itself. ---------------------------------- I'm outlining below a proposal for a RAID device mapper virtual block device for the kernel which adds "split raid" functionality on an incremental batch basis for a home media server/archived content which is rarely accessed. Given a set of N+X block devices (of the same size but smallest common size wins) the SplitRAID device mapper device generates virtual devices which are passthrough for N devices and write a Batched/Delayed checksum into the X devices so as to allow offline recovery of block on the N devices in case of a single disk failure. Advantages over conventional RAID: - Disks can be spun down reducing wear and tear over MD RAID Levels (such as 1, 10, 5,6) in the case of rarely accessed archival content - Prevent catastrophic data loss for multiple device failure since each block device is independent and hence unlike MD RAID will only lose data incrementally. - Performance degradation for writes can be achieved by keeping the checksum update asynchronous and delaying the fsync to the checksum block device. In the event of improper shutdown the checksum may not have all the updated data but will be mostly up to date which is often acceptable for home media server requirements. A flag can be set in case the checksum block device was shutdown properly indicating that a full checksum rebuild is not required. Existing solutions considered: - SnapRAID (http://snapraid.sourceforge.net/) which is a snapshot based scheme (Its advantages are that its in user space and has cross platform support but has the huge disadvantage of every checksum being done from scratch slowing the system, causing immense wear and tear on every snapshot and also losing any information updates upto the snapshot point etc) I'd like to get opinions on the pros and cons of this proposal from more experienced people on the list to redirect suitably on the following questions: - Maybe this can already be done using the block devices available in the kernel? - If not, Device mapper the right API to use? (I think so) - What would be the best block devices code to look at to implement? Regards, Anshuman Aggarwal

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Not getting printk output
by Mayank Nov. 27, 2014

Nov. 27, 2014

Hi, I am trying to print something to the kernel debug log level using printk, but while using dmesg i am not getting the output on the console. My /proc/sys/kernel/printk setting is 4 4 1 7. Please help Thanks, Mayank

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Your editor/IDE settings for autocompletion and other easiness
by Andrey Utkin Nov. 27, 2014

Nov. 27, 2014

(I was asked to research this topic to help students. So please ignore this topic if all you want to say is that it is OK to code in editor without autocompletion and any other integration, and that there's LXR website. We all know that.) Dear kernel developers, if you have a minute, please share - what's your configuration for editor integration with sources tree? (the opposite is "just using any editor") - which IDE/editor handiness options except autocompletion are possible to obtain while developing kernel code, and which options do you use? If you don't use any special configuration, feel free not to reply. Thanks! -- Andrey Utkin

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Nick in lkml ?
by Sudip Mukherjee Nov. 26, 2014

Nov. 26, 2014

hi all, I don't know if you have noticed or not , but Nick is back to lkml , and his patch has been accepted and applied on 19/11/2014 via commit 86619e7ba3991309b88969f9a2e5c7f2d014c680 but the only thing that surprises me is that i am not seeing any mail from Nick in lkml , but i am seeing mails which are sent in reply to Nick's mails. Does that mean Nick is intentionally not sending cc of his patch / mail to lkml ???

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how can grub get `code32_start`
by 孙建希 Nov. 26, 2014

Nov. 26, 2014

hello, x86 `protected_mode_jump` will use param `boot_params.hdr.code32_start`which bootloader should set. But how can grub get `code32_start`from kernel image?

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work queue
by 户户 Nov. 25, 2014

Nov. 25, 2014

I'm playing around with work_queue in my VMware workstation. but I hit a problem that the work is processed by [kworker/3:1] other than my work queue. static int __init test_init(void) { pr_info(" (*) test_init start - pid:%d. cpu:%d\n", current->pid, get_cpu()); int ret = 0; test_queue_ptr = create_workqueue("myfoo"); // test_queue_ptr = create_singlethread_workqueue("test_workqueue"); if(!test_queue_ptr){ goto test_queue_ptr_error; } INIT_WORK(&test_work, test_cb); // ret = queue_work(test_queue_ptr, &test_work); ret = queue_work_on(get_cpu(), test_queue_ptr, &test_work); // schedule_work(&test_work); pr_info(" (*) test_init - queue_work_on return:%d. \n", ret); return 0; test_queue_ptr_error: destroy_workqueue(test_queue_ptr); return 0; } static void test_cb(struct work_struct *work) { pr_info(" (*) test_cb - pid:%d. cpu:%d\n", current->pid, get_cpu()); } isnmod the module gives me the output : Nov 19 23:11:18 test kernel: [ 3031.766137] (*) test_init start - pid:8594. cpu:3 Nov 19 23:11:18 test kernel: [ 3031.766371] (*) test_init - queue_work_on return:1. Nov 19 23:11:18 test kernel: [ 3031.766672] (*) test_cb - pid:83. cpu:3 <--- this line indicates "test_cb" function is running on process 83 ([kworker/3:1]). ps aux .... root 82 0.0 0.0 0 0 ? S< 22:20 0:00 [charger_manager] root 83 0.0 0.0 0 0 ? S 22:20 0:00 [kworker/3:1] root 85 0.0 0.0 0 0 ? S 22:20 0:00 [kworker/0:2] root 217 0.0 0.0 0 0 ? S< 22:20 0:00 [mpt_poll_0] Thanks Jay

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systemctl equivalent of /sys/block/sda/device/state
by Chaitanya Gotkhindikar Nov. 24, 2014

Nov. 24, 2014

Hi folks, I am trying to port my old script to centos7, in which earlier device state was set using echo "offline" > /sys/block/sda/device/state. I am looking for systemctl equivalent for it. Can anyone please help? Thank you. -Chaitanya

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using SD card on Broadcom 4709 eval board
by Abu Rasheda Nov. 23, 2014

Nov. 23, 2014

I have been trying to use SD card on Broadcom's 4709 eval board. Linux kernel tree provided with SDK seems to have few SDIO drivers, but non of them seems to be working or more accurately, loading them does not list device in /proc/devices, so I can create block file to mount it. After googling and searching through Linux kernel tree, it seems like B43_SDIO is correct option to turn on, since the controller seems to be on the Broadcom CPU (4709) process itself (am I correct ?). So if B43_SDIO is correct option, I have not been able to turn it on (when running make menuconfig). as it is not showing up. depends on B43 && SSB_SDIOHOST_POSSIBLE && EXPERIMENTAL, off the above B43 is only shows up in arch/ppc, which does not make sense, as this CPU is arm based. Any guidance will be appreciated. Thanks

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the file with the same name
by 孙建希 Nov. 23, 2014

Nov. 23, 2014

hello, I found there's many files with same name in kernel. e.g: include/asm/linkage.h arch/x86/include/asm/linkage.h I know when compile for x86, kbuild will use x86 linkage.h. But how？use #ifndef or anything other?

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