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

user space device drivers
by Gergely Buday May 14, 2013

May 14, 2013

Hi there, I learned, e.g. from here that user space device drivers are indeed possible: http://www.makelinux.net/ldd3/chp-2-sect-9 Are there serious user space drivers in Linux? Could you name a few? Or, is this just for hacking a driver for your home-made hardware? - Gergely

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Mapping of ZONE_HIGHMEM in kernel address space in 32bit x86
by Paul Davies C May 14, 2013

May 14, 2013

In a system with 3:1 split, the ZONE_NORMAL with a size of 896MB is permanently mapped to the kernel address space.This leaves a 128MB free space in the Kernel address space and according to my understanding, the ZONE_HIGHMEM pages are mapped temporarily to this 128MB part. If the system actually had a 4GB physical memory you will be mapping(not smultaneously) the HIHGMEM part- which is roughly 3.2GB - to this 128MB part. If that was the case Kernel would have to frequently access HIHGMEM which implicates a frequent change in temporaty mapping and that in my view is a penalty. So what was the reason why ZONE_NORMAL fixed at 896MB and not something really lower? -- *Regards,* *Paul Davies C* vivafoss.blogspot.com

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bio size is always 4096
by neha naik May 14, 2013

May 14, 2013

Hi, I was under the impression that when the bio comes to a block device driver its size is variable. But, after writing a block device driver i realized that such is not the case and it always is 4096. Does this mean that by default if i don't use any merge function the bio will always have size 4096(meaning it will have only 1 page!!!!). Regards, Neha

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Initial git repository - kernel tree
by Kevin Wilson May 13, 2013

May 13, 2013

Hello, I have a question about git patches. When I run git log include/linux/skbuff.h and page down till the end, I reach 1da177e Linux-2.6.12-rc2 (I do it on the net-next tree.) git show 1da177e gives: Author: Linus Torvalds <torvalds(a)ppc970.osdl.org> Date: Sat Apr 16 15:20:36 2005 -0700 Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip! So this is the initial patch from 2005. Now, does it mean that prior to this patch all patches were not handled by git ? or was there some merging from an old tree to a new tree where history of git patches was removed in the new tree ? regards, Kevin

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Processor Comparison
by Robert Clove May 11, 2013

May 11, 2013

Hello All, I want to some process that too not of Intel. Does anyone know an site that can help me? And on what basis should i compare the processor? Thanks Rob

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unable to set smp_affinity of PCIe interrupt
by Amit Mahadik May 10, 2013

May 10, 2013

Hello, Following is the output of cat /proc/interrupts CPU0 CPU1 CPU2 200: 9634 0 0 PCIe0-MSI eth0 I want to change the processor affinity of the above PCIe interrupt By executing command echo 2 > /proc/irq/200/smp_affinity I get the following error sh: write error: Input/output error Even after changing the file permissions I have the same problem. I would like to know how to change the affinity of the above virtual interrupt?? Regards, Amit.

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Kernel routine to "lock" all of the pages of a particular VMA.
by Buland Kumar Singh May 9, 2013

May 9, 2013

Hi All, Is there a kernel routine ( not a system call ) that a kernel module can call to "lock" all of the pages of a particular VMA of a user process that is using the driver ? -- BKS

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what's the meaning of "%%fs" ?
by lx May 9, 2013

May 9, 2013

hi all: the codes is: extern inline unsigned char get_fs_byte(const char * addr) { unsigned register char _v; __asm__ ("movb %%fs:%1,%0":"=r" (_v):"m" (*addr)); return _v; } What's the meaning of "%%fs" ? Is " __asm__ ("movb %1,%0":"=r" (_v):"m" (*addr));" not ok? Thank you.

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what are gflags of net_device for?
by Andy Johnson May 9, 2013

May 9, 2013

Hi all, Any idea for what do we need gflags of net_device? I believe gflags stand for global flags (though the header file, netdevice.h, does not say so explicitly). I see that they are initialized only in __dev_change_flags() , in net/core/dev.c, in But it is not clear what is their meaning. Any ideas? can someone elaborate on this ? rgs, Andy

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cfs scheduler vruntime overflow
by 이승훈 May 9, 2013

May 9, 2013

hi all. I have a question about vruntime. it will not overflow? i know it's type is u64. but how about 32bit machine? i'm wating your help. Thanks, Earl 2013. 5. 9. 오전 1:01에 <kernelnewbies-request(a)kernelnewbies.org>님이 작성: Send Kernelnewbies mailing list submissions to kernelnewbies(a)kernelnewbies.org To subscribe or unsubscribe via the World Wide Web, visit http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies or, via email, send a message with subject or body 'help' to kernelnewbies-request(a)kernelnewbies.org You can reach the person managing the list at kernelnewbies-owner(a)kernelnewbies.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Kernelnewbies digest..." Today's Topics: 1. Re: current tty (richard -rw- weinberger) 2. Re: Documentation on device-mapper and friends (Greg Freemyer) 3. Re: Documentation on device-mapper and friends (neha naik) ---------------------------------------------------------------------- Message: 1 Date: Wed, 8 May 2013 14:24:10 +0200 From: richard -rw- weinberger <richard.weinberger(a)gmail.com> Subject: Re: current tty To: Hatte John <june.tune.sea(a)gmail.com> Cc: kernelnewbies <kernelnewbies(a)kernelnewbies.org> Message-ID: <CAFLxGvxeFRS-ojPjXYzMSZ9yRvfpCjLa%3D%2BwRo%3DUu7QiKVdP9bw(a)mail.gmail.com> Content-Type: text/plain; charset=UTF-8 On Wed, May 8, 2013 at 6:21 AM, Hatte John <june.tune.sea(a)gmail.com> wrote: > Hi? > > As I know .the /dev/tty is the current task's tty , which is stored to > current->tty , > My question is when does this value is assgined to current->tty ? As I told you on IRC, struct task_struct has no ->tty member. If your custom/old/whatever kernel has, use grep to find out... Thanks, //richard ------------------------------ Message: 2 Date: Wed, 8 May 2013 10:11:02 -0400 From: Greg Freemyer <greg.freemyer(a)gmail.com> Subject: Re: Documentation on device-mapper and friends To: Gaurav Mahajan <gauravmahajan2007(a)gmail.com> Cc: amit mehta <gmate.amit(a)gmail.com>, Linux Kernel List <kernelnewbies(a)kernelnewbies.org>, Anatol Pomozov <anatol.pomozov(a)gmail.com>, neha naik <nehanaik27(a)gmail.com> Message-ID: <CAGpXXZ%2BNFme9D%3DdMMDwZxYmVRxsS29oFqMv%3DVWrAVkvxQUOsig(a)mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 The block layers can be layered both ways. DM is the newer infrastructure and was created in the early days of 2.6 If what I was writing could fit into a dm-target, that is what I would do. There are significant projects like drbd and mdraid that are not dm-targets, but I think their is a long term goal to incorporate mdraid's functionality at a minimum into dm. I doubt drbd is ever moved to dm. It is just too big of a project and in use in lots of production server environments. Greg On Tue, May 7, 2013 at 1:46 AM, Gaurav Mahajan <gauravmahajan2007(a)gmail.com> wrote: > Hi Neha, > > LVM uses device mapper. Advantages of using device mapper is that you can > stack different dm-targets on each other. > I am really not aware of block device drivers. > > May be Greg can help us understand the actual pros and cons. > > Thanks, > Gaurav > > > On Wed, May 1, 2013 at 9:45 PM, neha naik <nehanaik27(a)gmail.com> wrote: >> >> Hi Gaurav, >> I went through your blog and it is really informative. But after reading >> that i realized that i have a question: >> If I want to write a block device driver which is going to sit on lvm >> (and do some functionality on top of it) then should i go for the block >> device driver api >> or write it as a device mapper target. What are the >> advantages/disadvantages of both the approaches. >> >> Regards, >> Neha >> >> >> On Tue, Apr 30, 2013 at 4:24 AM, Gaurav Mahajan >> <gauravmahajan2007(a)gmail.com> wrote: >>> >>> Hi Amit, >>> >>> I had compiled some notes on my blog. >>> Here are some links on writing your own device mapper target. >>> http://techgmm.blogspot.in/p/writing-your-own-device-mapper-target.html >>> >>> Concept of device mapper target. >>> http://techgmm.blogspot.in/p/device-mapper-layer-explored-every.html >>> >>> Thanks, >>> Gaurav. >>> >>> >>> On Tue, Apr 30, 2013 at 5:05 AM, Anatol Pomozov >>> <anatol.pomozov(a)gmail.com> wrote: >>>> >>>> Hi >>>> >>>> On Mon, Apr 29, 2013 at 9:51 AM, amit mehta <gmate.amit(a)gmail.com> >>>> wrote: >>>> > On Sun, Apr 28, 2013 at 5:24 PM, Greg Freemyer >>>> > <greg.freemyer(a)gmail.com> wrote: >>>> >> A nice diagram of the overall storage subsystem is at >>>> >> http://www.thomas-krenn.com/en/oss/linux-io-stack-diagram.html >>>> >> >>>> >> Dm is just a single block in it, but it can help to see where it fits >>>> >> in overall. >>>> >> >>>> >> Btw: that diagram doesn't show the legacy ata driver that creates >>>> >> /dev/hdx style devices. Has that been dropped while I wasn't paying >>>> >> attention? I haven't used it in years, but I thought it was still used on >>>> >> embedded systems. >>>> >> >>>> > >>>> > Thank you for sharing the link, but I'm looking for more >>>> > detailed information on I/O stack in Linux, dm-mapper and >>>> > multipath in particular. >>>> >>>> Some docs about multipath can be found here >>>> >>>> http://www.sourceware.org/lvm2/wiki/MultipathUsageGuide >>>> http://christophe.varoqui.free.fr/refbook.html >>>> >>>> The userspace part for tools is here >>>> http://sourceware.org/lvm2/ >>>> >>>> _______________________________________________ >>>> Kernelnewbies mailing list >>>> Kernelnewbies(a)kernelnewbies.org >>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>> >>> >>> >>> _______________________________________________ >>> Kernelnewbies mailing list >>> Kernelnewbies(a)kernelnewbies.org >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>> >> > ------------------------------ Message: 3 Date: Wed, 8 May 2013 09:15:26 -0600 From: neha naik <nehanaik27(a)gmail.com> Subject: Re: Documentation on device-mapper and friends To: Greg Freemyer <greg.freemyer(a)gmail.com> Cc: amit mehta <gmate.amit(a)gmail.com>, Linux Kernel List <kernelnewbies(a)kernelnewbies.org>, Anatol Pomozov <anatol.pomozov(a)gmail.com>, Gaurav Mahajan <gauravmahajan2007(a)gmail.com> Message-ID: <CAOb%3D_xKRuH4jzD%3Daue-HJP%2B%3DDxguPYwuaqie%3DsMvvYytvoXCcA(a)mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Hi Greg, Thanks for the information. I have another question :). Is there some less flexibility if we use device mapper target? For example in block device driver you can use the api such that it won't use the OS io scheduler, so the io comes directly to the block device driver through the 'make_request' call. With the device mapper i don't think that happens(looking at the api calls). Does this mean that stuff like io scheduling. barrier control etc is done by the device mapper itself and we can focus only on 'mapping' the io. Regards, Neha On Wed, May 8, 2013 at 8:11 AM, Greg Freemyer <greg.freemyer(a)gmail.com >wrote: > The block layers can be layered both ways. DM is the newer > infrastructure and was created in the early days of 2.6 > > If what I was writing could fit into a dm-target, that is what I would do. > > There are significant projects like drbd and mdraid that are not > dm-targets, but I think their is a long term goal to incorporate > mdraid's functionality at a minimum into dm. I doubt drbd is ever > moved to dm. It is just too big of a project and in use in lots of > production server environments. > > Greg > > On Tue, May 7, 2013 at 1:46 AM, Gaurav Mahajan > <gauravmahajan2007(a)gmail.com> wrote: > > Hi Neha, > > > > LVM uses device mapper. Advantages of using device mapper is that you can > > stack different dm-targets on each other. > > I am really not aware of block device drivers. > > > > May be Greg can help us understand the actual pros and cons. > > > > Thanks, > > Gaurav > > > > > > On Wed, May 1, 2013 at 9:45 PM, neha naik <nehanaik27(a)gmail.com> wrote: > >> > >> Hi Gaurav, > >> I went through your blog and it is really informative. But after > reading > >> that i realized that i have a question: > >> If I want to write a block device driver which is going to sit on lvm > >> (and do some functionality on top of it) then should i go for the block > >> device driver api > >> or write it as a device mapper target. What are the > >> advantages/disadvantages of both the approaches. > >> > >> Regards, > >> Neha > >> > >> > >> On Tue, Apr 30, 2013 at 4:24 AM, Gaurav Mahajan > >> <gauravmahajan2007(a)gmail.com> wrote: > >>> > >>> Hi Amit, > >>> > >>> I had compiled some notes on my blog. > >>> Here are some links on writing your own device mapper target. > >>> > http://techgmm.blogspot.in/p/writing-your-own-device-mapper-target.html > >>> > >>> Concept of device mapper target. > >>> http://techgmm.blogspot.in/p/device-mapper-layer-explored-every.html > >>> > >>> Thanks, > >>> Gaurav. > >>> > >>> > >>> On Tue, Apr 30, 2013 at 5:05 AM, Anatol Pomozov > >>> <anatol.pomozov(a)gmail.com> wrote: > >>>> > >>>> Hi > >>>> > >>>> On Mon, Apr 29, 2013 at 9:51 AM, amit mehta <gmate.amit(a)gmail.com> > >>>> wrote: > >>>> > On Sun, Apr 28, 2013 at 5:24 PM, Greg Freemyer > >>>> > <greg.freemyer(a)gmail.com> wrote: > >>>> >> A nice diagram of the overall storage subsystem is at > >>>> >> http://www.thomas-krenn.com/en/oss/linux-io-stack-diagram.html > >>>> >> > >>>> >> Dm is just a single block in it, but it can help to see where it > fits > >>>> >> in overall. > >>>> >> > >>>> >> Btw: that diagram doesn't show the legacy ata driver that creates > >>>> >> /dev/hdx style devices. Has that been dropped while I wasn't > paying > >>>> >> attention? I haven't used it in years, but I thought it was still > used on > >>>> >> embedded systems. > >>>> >> > >>>> > > >>>> > Thank you for sharing the link, but I'm looking for more > >>>> > detailed information on I/O stack in Linux, dm-mapper and > >>>> > multipath in particular. > >>>> > >>>> Some docs about multipath can be found here > >>>> > >>>> http://www.sourceware.org/lvm2/wiki/MultipathUsageGuide > >>>> http://christophe.varoqui.free.fr/refbook.html > >>>> > >>>> The userspace part for tools is here > >>>> http://sourceware.org/lvm2/ > >>>> > >>>> _______________________________________________ > >>>> Kernelnewbies mailing list > >>>> Kernelnewbies(a)kernelnewbies.org > >>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >>> > >>> > >>> > >>> _______________________________________________ > >>> Kernelnewbies mailing list > >>> Kernelnewbies(a)kernelnewbies.org > >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >>> > >> > > >

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