August 2014 - kernelnewbies@kernelnewbies.org

Board and OS suggestion
by Robert Clove Aug. 28, 2014

Aug. 28, 2014

Hi All, As much of you will be doing experiments i need your advice. I want to run some secure OS on an embedded platform like raspberry pi or beagle board. Can you suggest me which board is good and any secure OS that you have try'ed? Any board having wi fi connectivity will be an advantage. Regards

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Btrfs Issues
by nick Aug. 28, 2014

Aug. 28, 2014

When booting on an Ubuntu kernel I am hitting this in my dmesg with an external drive I have. I am wondering if this is a bug or just a common issue. 8518.918519] ------------[ cut here ]------------ [ 8518.918528] WARNING: CPU: 1 PID: 13778 at /build/buildd/linux-3.13.0/fs/btrfs/super.c:254 __btrfs_abort_transaction+0x50/0x110 [btrfs]() [ 8518.918529] btrfs: Transaction aborted (error -5) [ 8518.918530] Modules linked in: btrfs raid6_pq libcrc32c xor ses enclosure usb_storage bnep rfcomm bluetooth hid_generic usbhid hid eeepc_wmi asus_wmi sparse_keymap intel_rapl x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_codec_hdmi aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd serio_raw snd_hda_codec_realtek lpc_ich snd_hda_intel snd_hda_codec snd_hwdep snd_seq_midi snd_seq_midi_event snd_pcm snd_rawmidi snd_page_alloc fglrx(POF) snd_seq parport_pc snd_seq_device snd_timer ppdev wmi mei_me snd mei mac_hid lp parport soundcore amd_iommu_v2 video ahci libahci r8169 mii [ 8518.918560] CPU: 1 PID: 13778 Comm: umount Tainted: PF W O 3.13.0-34-generic #60-Ubuntu [ 8518.918561] Hardware name: System manufacturer System Product Name/P8Z68-V LE, BIOS 3506 01/17/2012 [ 8518.918562] 0000000000000009 ffff8801c9ad5c50 ffffffff8171bd94 ffff8801c9ad5c98 [ 8518.918564] ffff8801c9ad5c88 ffffffff810676cd 00000000fffffffb ffff880211d72800 [ 8518.918566] ffff8801c49d8000 ffffffffa0bb2e90 000000000000060b ffff8801c9ad5ce8 [ 8518.918568] Call Trace: [ 8518.918573] [<ffffffff8171bd94>] dump_stack+0x45/0x56 [ 8518.918576] [<ffffffff810676cd>] warn_slowpath_common+0x7d/0xa0 [ 8518.918578] [<ffffffff8106773c>] warn_slowpath_fmt+0x4c/0x50 [ 8518.918583] [<ffffffffa0b16f00>] __btrfs_abort_transaction+0x50/0x110 [btrfs] [ 8518.918591] [<ffffffffa0b40ebe>] cleanup_transaction+0x6e/0x290 [btrfs] [ 8518.918594] [<ffffffff810aaf00>] ? prepare_to_wait_event+0x100/0x100 [ 8518.918601] [<ffffffffa0b41e3a>] btrfs_commit_transaction+0x6ea/0x970 [btrfs] [ 8518.918608] [<ffffffffa0b3c00f>] btrfs_commit_super+0x8f/0xa0 [btrfs] [ 8518.918614] [<ffffffffa0b3dac0>] close_ctree+0x1e0/0x290 [btrfs] [ 8518.918617] [<ffffffff811d8c2c>] ? evict_inodes+0x11c/0x130 [ 8518.918622] [<ffffffffa0b139b9>] btrfs_put_super+0x19/0x20 [btrfs] [ 8518.918625] [<ffffffff811beda2>] generic_shutdown_super+0x72/0xf0 [ 8518.918627] [<ffffffff811befe2>] kill_anon_super+0x12/0x20 [ 8518.918631] [<ffffffffa0b15eb6>] btrfs_kill_super+0x16/0x90 [btrfs] [ 8518.918634] [<ffffffff811bf33d>] deactivate_locked_super+0x3d/0x60 [ 8518.918636] [<ffffffff811bf8f6>] deactivate_super+0x46/0x60 [ 8518.918638] [<ffffffff811dc5f6>] mntput_no_expire+0xd6/0x170 [ 8518.918640] [<ffffffff811ddb6e>] SyS_umount+0x8e/0x100 [ 8518.918642] [<ffffffff8172c97f>] tracesys+0xe1/0xe6 [ 8518.918644] ---[ end trace 1a6b295c1d8ad4c3 ]--- Nick

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Curious about corner case in btrfs code
by Nick Aug. 27, 2014

Aug. 27, 2014

After reading through the code in inode.c today , I am curious about the comment and the following code I will paste below. I am curious if this corner case is hit often enough for me to write a patch to improve the speed of this corner case. Furthermore , compress_file_range is the function name, in case you can't guess by the pasted code. Regards Nick 411 /* 412 * we don't want to send crud past the end of i_size through 413 * compression, that's just a waste of CPU time. So, if the 414 * end of the file is before the start of our current 415 * requested range of bytes, we bail out to the uncompressed 416 * cleanup code that can deal with all of this. 417 * 418 * It isn't really the fastest way to fix things, but this is a 419 * very uncommon corner. 420 */ 421 if (actual_end <= start) 422 goto cleanup_and_bail_uncompressed;

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cdev_init and struct file_operations
by John de la Garza Aug. 27, 2014

Aug. 27, 2014

In the book Linux Device Drivers a struct cdev is setup like this: static void scull_setup_cdev(struct scull_dev *dev, int index) { int err, devno = MKDEV(scull_major, scull_minor + index); cdev_init(&dev->cdev, &scull_fops); dev->cdev.owner = THIS_MODULE; dev->cdev.ops = &scull_fops; ... the code for cdev_init does this: void cdev_init(struct cdev *cdev, const struct file_operations *fops) { memset(cdev, 0, sizeof *cdev); INIT_LIST_HEAD(&cdev->list); kobject_init(&cdev->kobj, &ktype_cdev_default); cdev->ops = fops; } Why does the code from ldd3 set dev->cdev.ops = &scull_fops again? Doesn't cdev_init already do that?

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Hi I'm new here
by Bowen Aug. 27, 2014

Aug. 27, 2014

I am just a new man in kernel development, there is a question bother me for a time. Is it neccessary to have a virtual machine when developing or debugging kernel? Thanks.

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which function can replace “create_proc_info_entry” in 2.6.32 of Linux kernel?
by lxgeek Aug. 27, 2014

Aug. 27, 2014

hi all: The 2.6.32 kernel don't have the function of "create_proc_info_entry". Which function can replace it? Thank you.

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Workflow improvements when sending patches with format-patch && send-email ?
by Matthias Beyer Aug. 27, 2014

Aug. 27, 2014

Hi, I have a problem related to my workflow when patching kernel sources. What I do by now, when sending patches: scripts/get_maintainer.pl --file my/patched/file.c git format-patch -s -n --cover-letter # and then appending _every single mail from the get_maintainer.pl # call with either --to or --cc # and the commit range git send-email --no-chain-reply-to # and then appending _every single mail from the get_maintainer.pl # call with either --to or --cc ./00* The second step is mainly copy-paste from the format-patch call, but I guess you already notice my issue: I have to "hand-copy" every email address from the get_maintainer.pl call. I also send my patches to two persons which do not get listed from the get_maintainer.pl call most of the time, plus I do not send my patches to the LKML directly (but the driverdev ML). I consider this hard work, especially when having a lot of _small_ patchsets, as I do this for every single patchset and it really annoys me. Are there tools somewhere to simplify these steps? Something like "generate & send patches from bla-blubb...foobazbar" and then it: 1) Gets mailaddrs from get_maintainer.pl 2) lets me add additional and delete receivers 3) asks me which one gets a --to and which one a --cc 4) generates the patches with format-patch 5) (optionally) runs checkpatch.pl on it 6) sends the patches with send-email after confirmation Are there some tools out there? Or how do you guys do this? Or are there tweaks built-in in git that I don't know yet? -- Mit freundlichen Grüßen, Kind regards, Matthias Beyer Proudly sent with mutt. Happily signed with gnupg.

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values from pci_dev or read from config space - pci
by Oscar Salvador Aug. 26, 2014

Aug. 26, 2014

Hi everybody! I was thinking about post this question in the linux-pci list, but I'm not sure if this question is very basic for it, so maybe it's better aks here. If not, I'll ask there. My question is about that I'm writing a driver for a old realtek network card, only for learning purposes, and I was conviced that I could read the values from the config space( values related to IRQ, I/O memory regions), examples: pci_read_config_byte(dev, IRQ_OFFSET, &irq); rtiomemr_start = pci_resource_start(dev, IO_MEM); rtiomemr_len = pci_resource_len(dev, IO_MEM); rtiomemr_end = pci_resource_end(dev, IO_MEM); But then I read in the Documentation/pci.text that the correct way to achieve this values are reading the valzes stored in the pci_dev structure. Actually, with the values from I/O memory regions I didn't have any problem, but I got a different values for IRQ. If I get the IRQ from the pci_dev, I get a X, but if I get the IRQ from the config space, I get another different number Y. Would be you so kind to explain: 1- Why it's better use the values stored in pci_dev structure instead of read from config space. 2- Why the IRQ number is different? (Maybe this question is answered with the first question hehe) Thank you very much Best regards

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Writing makefiles for headers outside 'usr/include'
by testlaster Aug. 26, 2014

Aug. 26, 2014

So the initial problem I'm having is that wanting to use headers and their libs like|module.h|and|init.d|and|pci.h|for instance can't be used by simply going|#include <pci.h>|because if you check the actual|pci.h|||(40 lines or so) file you will find that its allot shorter then the usual dev|pci.h| so needless to say you can't use all the functions. So now I have to use makefiles to point to other directories. I've been trying to create makefiles but at the moment the errors just rack up so much that I really don't know what part of the process is at fault. Is it the C or the headers or the wrong libraries? I'm kind of clueless to where the libraries might even be. Could someone please help me write a makefile for Linux headers and their libraries that is not in the usual|/usr/include|directory? The source files that I want to use will be in|usr/src/linux-headers-3.13.0.32-generic/include|. Also if they are in the makefile how will I include them in the source? I've been learning a lot of things in parallel and I think the curve is starting to get to me. :/

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a question on linux header extraction
by Chan Kim Aug. 26, 2014

Aug. 26, 2014

Hello, I'm using linux3.3 and recently while building busybox for a new command, found the BB uses linux kernel headers. So I looked up the internet and did 'make headers_install ARCH=.. CROSS_COMPILE=.. INSTALL_HDR_PATH=..'. Then I used the new header files instead of files under sparc-snake-linux/sys-include. But I had to copy over some missing files from the sys-include to the new header directories and had to copy some missiong definitions from the sys-include files to the corresponing file in the new header files. Is this what I am supposed to do? (why are there some missing files? Doesn't it work well for versions later than 2.6?) And do I have to build the glibc again with this new header files? (I'm using glibc for busybox) any help would be deeply appreciated. Thanks Chan

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