February 2012 - kernelnewbies@kernelnewbies.org

[question] v4l read() operation
by Ezequiel García Feb. 28, 2012

Feb. 28, 2012

Hi, If I register a video device with this fops: static const struct v4l2_file_operations v4l2_fops = { .owner = THIS_MODULE, .open = xxx_open, .unlocked_ioctl = xxx_unlocked_ioctl, .poll = xxx_poll, .mmap = xxx_mmap, }; then if I "cat" the device $ cat /dev/video0 Who is supporting read() ? I thought it could be v4l2_read(), however this function seems to return EINVAL: static ssize_t v4l2_read(struct file *filp, char __user *buf, size_t sz, loff_t *off) { struct video_device *vdev = video_devdata(filp); int ret = -ENODEV; if (!vdev->fops->read) return -EINVAL; if (vdev->lock && mutex_lock_interruptible(vdev->lock)) return -ERESTARTSYS; if (video_is_registered(vdev)) ret = vdev->fops->read(filp, buf, sz, off); if (vdev->lock) mutex_unlock(vdev->lock); return ret; } Thanks, Ezequiel.

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Initramfs error during boot
by Sertaç Olgunsoylu Feb. 27, 2012

Feb. 27, 2012

Hi all, I built stable tree and latest(linus' tree) with default configuration and then installed them on my laptop. However, when I try to boot my system with kernels that I built, it cannot boot. It freezes just after selection made on GRUB and nothing is printed on the display. I managed to get following error by booting system in recovery mode: Starting up ... mount: mounting /dev/disk/by-uuid/48bfb57f-4750-4537-b563-7094743c161e on /root failed: Invalid argument mount: mounting /dev on /root/dev failed: No such file or directory mount: mounting /sys on /root/sys failed: No such file or directory mount: mounting /proc on /root/proc failed: No such file or directory Target filesystem doesn't have requested /sbin/init. No init found. Try passing init= bootarg. I build kernel with following commands: make O=../build defconfig make O=../build -j2 sudo make O=../build modules_install install You could see grub.cfg entries below for both (custom build kernel and stock build kernel): # Custom build menuentry 'Ubuntu, with Linux 3.2.7' --class ubuntu --class gnu-linux --class gnu --class os { recordfail set gfxpayload=$linux_gfx_mode insmod gzio insmod part_msdos insmod ext2 set root='(hd0,msdos3)' search --no-floppy --fs-uuid --set=root 48bfb57f-4750-4537-b563-7094743c161e linux /boot/vmlinuz-3.2.7 root=UUID=48bfb57f-4750-4537-b563-7094743c161e ro quiet splash vt.handoff=7 initrd /boot/initrd.img-3.2.7 } # Stock build menuentry 'Ubuntu, with Linux 3.0.0-16-generic' --class ubuntu --class gnu-linux --class gnu --class os { recordfail set gfxpayload=$linux_gfx_mode insmod gzio insmod part_msdos insmod ext2 set root='(hd0,msdos3)' search --no-floppy --fs-uuid --set=root 48bfb57f-4750-4537-b563-7094743c161e linux /boot/vmlinuz-3.0.0-16-generic root=UUID=48bfb57f-4750-4537-b563-7094743c161e ro quiet splash vt.handoff=7 initrd /boot/initrd.img-3.0.0-16-generic }

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task_struct's real_parent vs parent members
by Vimal Feb. 27, 2012

Feb. 27, 2012

Hi, I am looking through kernel 3.2's task_struct, which has two pointers for parents: real_parent and parent (http://lxr.free-electrons.com/source/include/linux/sched.h#L1313) I would like to know why there are two pointers, and how these two differ. init_task's parent and real_parent are initialised to point to itself. Since the main way processes are created is through fork()/clone(), I tried following do_fork function to see where a newly created process's parent is set, but I am unable to find it. I see that do_fork dups the current task_struct, and only updates the new process's real_parent, depending on flags (passed via clone/fork syscall). The documentation in sched.h:1313 says that "parent" refers to the parent task that would receive SIGCHLD (i.e., the one that issues wait4()). I followed the wait4() syscall to do_wait(), I still am not able to find where the task's parent is updated. Is there something I'm missing? Thanks, -- Vimal

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Re: USB CDC ethernet interface from Ubuntu on VirtualBox to Windows 7
by Manavendra Nath Manav Feb. 27, 2012

Feb. 27, 2012

On Mon, Feb 27, 2012 at 11:53 PM, Greg KH <gregkh(a)linuxfoundation.org> wrote: > On Mon, Feb 27, 2012 at 11:46:34PM +0530, Manavendra Nath Manav wrote: >> On Mon, Feb 27, 2012 at 1:13 PM, Manavendra Nath Manav >> <mnm.kernel(a)gmail.com> wrote: >> > Hi All, >> > >> > I am having a USB CDC ethernet device whose driver exists only for >> > Linux. However, my end application needs to run on Windows. So, I have >> > set up Ubuntu 11.10 on Virtual Box running on Windows-7. Ubuntu is >> > able to register the device but not able to open an interface for it, >> > say eth1, etc. >> > >> > [ 382.531901] usb 2-1: new full speed USB device number 4 using uhci_hcd >> > [ 392.992690] cdc_ether: probe of 2-1:2.0 failed with error -32 >> > >> > e518816@ubuntu:~$ lsusb >> > Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub >> > Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub >> > Bus 002 Device 002: ID 0e0f:0002 VMware, Inc. Virtual USB Hub >> > Bus 002 Device 004: ID 0e1e:0800 >> > e518816@ubuntu:~$ >> > >> > My device is "Bus 002 Device 004". How to enable USB CDC ethernet on >> > this device and expose this interface to Windows using a loop-back >> > adapter. Any solution on VMware would also be helpful. >> > >> > -- >> > Manavendra Nath Manav >> >> Any inputs about what might be the problem. I am able to register the >> device perfectly on standalone Linux machine but on Linux running on >> Virtual box, USB CDC ethernet device is not able to register. Any help >> would be greatly appreciated. > > As this is a Windows issue, combined with virtual box, I suggest you ask > on a virtualbox mailing list, there's nothing we can do here, sorry. > > best of luck, > > greg k-h Okay, I will post in Virtual box mailing list too. Just a small query, what does "[usb probe] failed with error -32" means here? I am just curious to know can we reverse engineer the root cause by looking at this error. -- Manavendra Nath Manav

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USB CDC ethernet interface from Ubuntu on VirtualBox to Windows 7
by Manavendra Nath Manav Feb. 27, 2012

Feb. 27, 2012

Hi All, I am having a USB CDC ethernet device whose driver exists only for Linux. However, my end application needs to run on Windows. So, I have set up Ubuntu 11.10 on Virtual Box running on Windows-7. Ubuntu is able to register the device but not able to open an interface for it, say eth1, etc. [ 382.531901] usb 2-1: new full speed USB device number 4 using uhci_hcd [ 392.992690] cdc_ether: probe of 2-1:2.0 failed with error -32 e518816@ubuntu:~$ lsusb Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 002 Device 002: ID 0e0f:0002 VMware, Inc. Virtual USB Hub Bus 002 Device 004: ID 0e1e:0800 e518816@ubuntu:~$ My device is "Bus 002 Device 004". How to enable USB CDC ethernet on this device and expose this interface to Windows using a loop-back adapter. Any solution on VMware would also be helpful. -- Manavendra Nath Manav

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pagetables used in interrupt context
by subin gangadharan Feb. 27, 2012

Feb. 27, 2012

Hi All, Please correct me if I am wrong. In linux each process will have its own page tables, so when a interrupt happens processor will switch to interrupt context and execute the proper handler. So my doubt, if this is the case, interrupt hanlder will be using the pagetables of the interrupted process or is there a separate page table for this. -- With Regards Subin Gangadharan I am not afraid and I am also not afraid of being afraid.

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Problem regarding TRILL encapsulated frames
by Syed Muhammad Mohsin Kazmi Feb. 27, 2012

Feb. 27, 2012

hi all, I have written a code which encapsulates the bridge forwarding traffic with TRILL header for OTHERHOST and OUTGOING and send it by calling a function (forward). On the other side, these packets are received by (br_handle_frames), where i call a function (decapsulate_trill_header) within a check ethernet_type == 0x88c8 (as this is ether_type for trill protocol). But trill encapsulated packets have not processed there. When i ran the Wireshark and captured the outgoing traffic from sending side and incoming traffic from receiving side. These encapsulated packets are shown as LLC packets on both sending and receiving sides. I don't know why these packets are shown as LLC. I am trapped here. I have no idea , what should i do now. I need some help, suggestion or tactics to resolve this problem. regards, Mohsin Kazmi

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Re: Building kernel source
by Vladimir Murzin Feb. 26, 2012

Feb. 26, 2012

Hi, Distro specific methods already include idea form the kernel README file, i.e. they usually call make & co stuff. The difference in some extra commands to wrap kernel image into package. Advantage of using distro specific method is capability to manage your custom kernel with package manager. Best wishes Vladimir Murzin ------Original Message------ From: Sertaç Olgunsoylu Sender: kernelnewbies-bounces(a)kernelnewbies.org To: kernelnewbies(a)kernelnewbies.org ReplyTo: sertacolgunsoylu(a)gmail.com Subject: Building kernel source Sent: 27 Feb 2012 02:18 Hi, In the kernel README file, it is written following commands to build kernel: make config make sudo make modules_install install Also, there are some other distro specific methods to build kernel such as make-kpkg. Does it matter which one of them is being used to build kernel? Should I stick to commands given in the README file or using distro specific utilities is OK too? _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies Best wishes, Vladimir Murzin

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Building kernel source
by Sertaç Olgunsoylu Feb. 26, 2012

Feb. 26, 2012

Hi, In the kernel README file, it is written following commands to build kernel: make config make sudo make modules_install install Also, there are some other distro specific methods to build kernel such as make-kpkg. Does it matter which one of them is being used to build kernel? Should I stick to commands given in the README file or using distro specific utilities is OK too?

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Check if specific functionally is built into the kernel
by Arokux B. Feb. 26, 2012

Feb. 26, 2012

Dear all, I have the following problem. Some functionality can be either built into the kernel or it can be build as a module. In the latter case the application should load the module. Is there a general approach to test if specific functionality is built statically or as a module? Thanks Arokux

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