March 2013 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

why not choose another way to define the _IOC_xxxMASK related to the ioctl
by RS March 30, 2013

March 30, 2013

it defines in the kernel: #define _IOC_NRMASK ((1 << _IOC_NRBITS)-1) //define ... #define _IOC_NRSHIFT 0 ... #define _IOC_DIR(nr) (((nr) >> _IOC_DIRSHIFT) & _IOC_DIRMASK) //when decode why not define it like this: #define _IOC_NRSHIFT 0 ... #define _IOC_NRMASK ((_IOC_NRSHIFT >> _IOC_NRBITS) - _IOC_NRSHIFT) //define ... #define _IOC_DIR(nr) ((nr & _IOC_DIRMASK) >> _IOC_DIRSHIFT) // when decode I think it is better for the word "mask" .

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Creating mkfs for my custom filesystem
by Sankar P March 29, 2013

March 29, 2013

Hi, I am trying to write a simple filesystem to learn the basics of it. I have decided on a simple layout for my filesystem where the first block will be the super block and will contain the version information etc. The second block will contain the list of inodes. Third block onwards will be data blocks. Each file can grow only up to a single block size. Thrid block will represent the first file, fourth block for the second file and so on. Directories will not be supported. Now I want to create a mkfs for my filesystem as mentioned above. But I am not able to find out how to do the mkfs for my filesystem such that the generic mkfs utility will understand my filesystem. What APIs should I be using ? Any help is appreciated. Thanks. -- Sankar P http://psankar.blogspot.com

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Fwd: Creating mkfs for my custom filesystem
by Pranay Srivastava March 29, 2013

March 29, 2013

---------- Forwarded message ---------- From: Pranay Srivastava <pranjas(a)gmail.com> Date: Fri, 29 Mar 2013 15:53:21 +0530 Subject: Re: Creating mkfs for my custom filesystem To: Sankar P <sankar.curiosity(a)gmail.com> On 3/29/13, Sankar P <sankar.curiosity(a)gmail.com> wrote: > Hi, > > I am trying to write a simple filesystem to learn the basics of it. > > I have decided on a simple layout for my filesystem where the first > block will be the super block and will contain the version > information etc. The second block will contain the list of inodes. > Third block onwards will be data blocks. Each file can grow only up to > a single block size. Thrid block will represent the first file, fourth > block for the second file and so on. Directories will not be > supported. > > Now I want to create a mkfs for my filesystem as mentioned above. But > I am not able to find out how to do the mkfs for my filesystem such > that the generic mkfs utility will understand my filesystem. What APIs > should I be using ? > > Any help is appreciated. Thanks. > > -- > Sankar P > http://psankar.blogspot.com > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > Hi Sankar, I started with something like that. Although I wrote just a bit more complex but it really is quite simple. If you want you can use this and I'll also like to contribute to it. https://github.com/pranjas/psfs.git Checkout psfs.h and psfs-format.c for complete details. Let me know if you need any help. ---P.K.S---

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Re: Re: elf_map: why offset of vma need to subtract eppnt->p_vaddr ?
by Prabhu nath March 29, 2013

March 29, 2013

On Fri, Mar 29, 2013 at 3:03 PM, Jacky <jackyclivia(a)163.com> wrote: > > Great ! Thanks Prabhunath. > > Let me make sure I understand you correctly: > > Substracting ELF_PAGEOFFSET(eppnt->p_vaddr) from variable off makes vma > map the page-aligned file contents, right ? > Small change : Substracting ELF_PAGEOFFSET(eppnt->p_vaddr) from variable eppnt->p_offset makes vma map the page-aligned file contents > > 在 2013-03-29 16:56:29，"Prabhu nath" <gprabhunath(a)gmail.com> 写道： > > > > On Fri, Mar 29, 2013 at 12:45 PM, Jacky <jackyclivia(a)163.com> wrote: > >> Hi All, >> >> When mmaping elf image into memory, why offset vma need to subtract >> eppnt->p_vaddr as the following code ? >> >> static unsigned long elf_map() >> { >> ... >> unsigned long off = eppnt->p_offset - ELF_PAGEOFFSET(eppnt->p_vaddr); >> ... >> } >> > Assume you have logically divided the contents of the ELF file into > chunks of PAGE_SIZE (Typically 4K on x86). Let us name each chunk as *file > page*-synonym to *page frame* in the physical address space and *page* in > the virtual address space respectively. > Here variable *off* is the *file page* base offset - synonym to page base > address or page frame base address which are typically multiple of > PAGE_SIZE. > > off >> PAGE_SHIFT is the value stored in *vm_pgoff* in struct > vm_area_struct > In a nutshell vm_pgoff is the page number (*file page *number) in the ELF > file where the corresponding PT_LOAD segment starts. > > Suppose if a file offset (eppnt->p_offset) of a PT_LOAD segment is 9560 > (0x2558) bytes into the file and eppnt->p_vaddr is 0x08048558. Then the > file page number base address *off* is calculated as > > off = 0x2558 - 0x558; // ELF_PAGEOFFSET(eppnt->p_vaddr) > will expand to 0x558. > Then off is 0x2000 and vm_pgoff is (off >> PAGE_SHIFT) = 2. This means > that the PT_LOAD segment starts at 2nd page or 2nd file page in the ELF > file. > > > Thanks in advance. >> >> Jacky >> > > -- > Regards, > Prabhunath G > Linux Trainer > Bangalore > > > > -- Regards, Prabhunath G Linux Trainer Bangalore

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elf_map: why offset of vma need to subtract eppnt->p_vaddr ?
by Jacky March 29, 2013

March 29, 2013

Hi All, When mmaping elf image into memory, why offset vma need to subtract eppnt->p_vaddr as the following code ? static unsigned long elf_map() { ... unsigned long off = eppnt->p_offset - ELF_PAGEOFFSET(eppnt->p_vaddr); ... } Thanks in advance. Jacky

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initramfs_list
by ishare March 27, 2013

March 27, 2013

I am do some test on kernel 2.6.0 and encountering an problem about initramfs . I find my initramfs generated without a initramfs_list file ,which describes the list of files that will be created into the initramfs file . such as /sbin/init /etc ... Of course , this version surpports initramfs . Is there advice here ? thanks in advance!

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Driver managing network interface
by Pietro Paolini March 27, 2013

March 27, 2013

Hello, I know how retrieve the module from a char device but how can I find the module name behind the eth0 interface or more generally of a network interface ? Best Regards, Pietro.

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cap on writeback?
by Raymond Jennings March 27, 2013

March 27, 2013

Just curious, is there a cap on how much data can be in "writeback" at the same time? I'm asking because I have over a gigabyte of data in "dirty", but during flush, only about 60k or so is in writeback at any one time. Is there a cap of sorts, and if so, how do I remove it?

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what does the kernel does after it is being notified of incoming Frame
by Tarun Batra March 26, 2013

March 26, 2013

Hello All, I was trying to search "what happen when the kernel is being notified of the incoming Frame". I studied Chapter 10. Frame Reception Of "Understanding Linux Network Internals". I only tells how the kernel is notified of the coming frame. But what does the kernel does after it is being notified. I want to dig more deep. Can you give me more references even linked videos. Thanks

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BFQ: simple elevator
by Raymond Jennings March 25, 2013

March 25, 2013

I've been pondering making a very simple IO scheduler one step above noop, just keeps everything in a big heap sorted by position and a single cursor bouncing from head to tail shaving off requests in a loop of ascending and descending sweeps. Any gotchas I need to be aware of or can I simply fork off of deadline and simplify it to omit batching?

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