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Problem in building,installing new vanilla kernel - initramfs
by Vaibhav Jain July 10, 2011

July 10, 2011

Hi, For the past 2 weeks I have been trying to compile and install a new vanilla kernel (v2.6.39.2) on my debian and ubuntu vmware machines. But it is failing due to some problem related to initramfs. After compiling and installing the kernel and modules I am trying to create the initramfs image by using the command "update-initramfs -c -k 2.6.39.2". The command executes successfully and creates an initramfs image. However on booting the new kernel an error occurs and it takes me to the initramfs prompt. I tried it first on debian virtual machine and then on ubuntu virtual machine but failed on both. For building and installing the kernel I am NOT using any distribution-specific tools. Any help would be greatly appreciated. Thanks Vaibhav Jain

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Adding new function to existing driver ops
by Asha R July 8, 2011

July 8, 2011

Hi, I would like to know how to add new function to a driver in Linux Framework? For eg: In GPIO driver, there is gpio_chip structure defined. static struct gpio_chip mygpio_chip = { .label = "mygpio", .owner = THIS_MODULE, .direction_input = mygpio_direction_input, .get = mygpio_get, .direction_output = mygpio_direction_output, .set = mygpio_set, .to_irq = mygpio_to_irq, }; If i want to add *mygpio_pulldown* or *mygpio_altfunc* to support few more gpio functionalities, how and where can i add these functions in the structure? Any suggestions on this will be appreciated. Thanks in advance, Asha

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Re:Re: Query about UIO
by bill July 8, 2011

July 8, 2011

At 2011-07-08 02:37:46，"Hans J. Koch" <hjk(a)hansjkoch.de> wrote: >On Thu, Jul 07, 2011 at 07:15:25AM -0700, Greg KH wrote: >> On Thu, Jul 07, 2011 at 03:32:54PM +0800, bill wrote: >> > Hi, Greg >> > >> > I've been reading the UIO code, one place puzzled me a lot. >> > May I ask one question about it? >> > >> > ------------------------------------------------------------------------------- >> > drivers/uio/uio.c >> > static int uio_find_mem_index(struct vm_area_struct *vma) >> > { >> > int mi; >> > struct uio_device *idev = vma->vm_private_data; >> > >> > for (mi = 0; mi < MAX_UIO_MAPS; mi++) { >> > if (idev->info->mem[mi].size == 0) >> > return -1; >> > if (vma->vm_pgoff == mi) >> > return mi; >> > } >> > return -1; >> > } >> > >> > I don't get it why use vma->vm_pgoff as the index for struct uio_mem mem[MAX_UIO_MAPS], >> > Suppose there are twohardware memory space, if user intends to map the 2nd mem, then >> > the last parameter of mmap should be 1, >> > >> > mapaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, >> > fd, 1); >> > >> > Is my understanding correct? > >No, it isn't. The last parameter of mmap is divided by PAGE_SIZE before it >reaches the UIO core. Therefore, it has to be set to n * getpagesize(). >This is explained in the docs under Documentation/DocBook/. >Use "make htmldocs" to generate HTML documentation. A faster way is to do > >dblatex Documentation/DocBook/uio-howto.tmpl > >This generates a PDF with the UIO documentation, provided you have a working >LaTeX system, and have dblatex installed. > >Thanks, >Hans > Thanks for your explanation. So vma->vm_pgoff is not used as its original meanings, that's the point puzzled me. Now it's clear:) >> >> I really don't know, sorry. >> >> But Hans should know, Hans? >> >>

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Problem loading page in http://janitor.kernelnewbies.org/
by esmaeil mirzaee July 7, 2011

July 7, 2011

Hi I try to reach to link http://janitor.kernelnewbies.org/ but I've got error Problem loading page my connection is stable I can reach to other link but have problem with this page. Any suggestion is appreciate it. Thanks in advance. esmaeil PS: Apologize for weak in English and two times send.

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Query about UIO
by bill July 7, 2011

July 7, 2011

Hi, Greg I've been reading the UIO code, one place puzzled me a lot. May I ask one question about it? ------------------------------------------------------------------------------- drivers/uio/uio.c static int uio_find_mem_index(struct vm_area_struct *vma) { int mi; struct uio_device *idev = vma->vm_private_data; for (mi = 0; mi < MAX_UIO_MAPS; mi++) { if (idev->info->mem[mi].size == 0) return -1; if (vma->vm_pgoff == mi) return mi; } return -1; } I don't get it why use vma->vm_pgoff as the index for struct uio_mem mem[MAX_UIO_MAPS], Suppose there are twohardware memory space, if user intends to map the 2nd mem, then the last parameter of mmap should be 1, mapaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 1); Is my understanding correct? thanks bill

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Re: interview question how does application connects to device
by Mandeep Sandhu July 7, 2011

July 7, 2011

> How would using sysfs be useful if we were to talk about interacting with, let's say, a file system? ioctl's are quite versatile and rather easy to use when one wants to interact with a given FS. > > For instance, one can manage a Btrfs file system by using an user-level tool, which heavily uses ioctl's. Requiring it to interact with sysfs instead seems like complicating something simple with no apparent purpose. Franlky, I've never used the sysfs interface and mostly know it from 'theoretical' view-point. It was created mostly for providing a uniform way for user-space applications (udev/HAL, driver tools, etc) to interact with a device driver. It exposes the underlying device topology as a directory tree. I'm not sure how sysfs applies to 'filesystem' as it depicts a particular 'device hierarchy tree' within a kernel. As Greg mentioned here, lot filesystem drivers still prefer to use the ioctl interface. However, one use for it which I can see, is for controlling the underlying block device (hard-disk, USB mass storage etc). HTH, -mandeep

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performance about use Linux as a router
by jiangtao.jit July 7, 2011

July 7, 2011

dear all: i have a x86 PC and i use it as a router the kernel is 2.6.38 there are two NICs: eth0 and eth1 i configed eth0 as 10.1.0.1 and eth1 as 11.1.0.1 Linux will route between these two cards and it worked ok in the old days but recently, i had added a new NIC as eth2 for LAN so i add a bridge br0 and config it as 10.1.0.1 then i configed eth0 and eth2 under br0 no ip on eth0 now like br0(10.1.0.1) eth1(11.1.0.1) / \ eth0 eth2 | | LAN LAN i expected that the performance will be better but unfortunately things become worse the PC lost packets now at first, i think maybe there is a loop Under br0, so i disconnected the wire on eth2 or eth0 nothing changed, packets still lost then i remove br0 config is as before its' eth0(10.1.0.1) eth1(11.1.0.1) | LAN then everthing becomes fine, no packet lost i can't explain why, any idea? thanks 2011-07-06 jiangtao.jit

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can we enable perf during the kernel initialization?
by Da Zheng July 7, 2011

July 7, 2011

Hello, Does the current kernel allow us to enable perf during the kernel initialization? perf is initialized in a very early stage, but I cannot find any kernel parameters that can enable perf. Has anyone tried to use perf to profile the kernel during its initialization? Thanks, Da

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How to profile the kernel during its initialization?
by Zheng Da July 7, 2011

July 7, 2011

Hello Can we profile the kernel during its initialization? perf is initialized in an early stage in start_kernel(), but it seems there are no command-line parameters to enable it. Does anyone have any ideas how to profile the kernel during its initialization (before user space programs start to run)? I think someone should have the similar problem as me, and there should be some solutions. Thanks, Da

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performance about use Linux as a router
by jiangtao.jit July 6, 2011

July 6, 2011

dear all: i have a x86 PC and i use it as a router the kernel is 2.6.38 there are two NICs: eth0 and eth1 i configed eth0 as 10.1.0.1 and eth1 as 11.1.0.1 Linux will route between these two cards and it worked ok in the old days but recently, i had added a new NIC as eth2 for LAN so i add a bridge br0 and config it as 10.1.0.1 then i configed eth0 and eth2 under br0 no ip on eth0 now like br0(10.1.0.1) eth1(11.1.0.1) / \ eth0 eth2 | | LAN LAN i expected that the performance will be better but unfortunately things become worse the PC lost packets now at first, i think maybe there is a loop Under br0, so i disconnected the wire on eth2 or eth0 nothing changed, packets still lost then i remove br0 config is as before its' eth0(10.1.0.1) eth1(11.1.0.1) | LAN then everthing becomes fine, no packet lost i can't explain why, any idea? thanks 2011-07-06 jiangtao.jit

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