November 2011 - kernelnewbies@kernelnewbies.org

sd_prep_fn
by sumeet gandhare Nov. 11, 2011

Nov. 11, 2011

Hi All, I am trying to understand the scsi upper layer and middle layer code and found the function sd_prep_fn which seems to convert a request to a scsi command. I want to know when this function sd_prep_fn gets invoked. It seems sd_probe_async invokes blk_queue_prep_rq <http://lxr.linux.no/linux+*/+code=blk_queue_prep_rq>(sdp <http://lxr.linux.no/linux+*/+code=sdp>->request_queue <http://lxr.linux.no/linux+*/+code=request_queue>, sd_prep_fn <http://lxr.linux.no/linux+*/+code=sd_prep_fn>); Further following code is invoking the prep_rq_fn which is the blk_peek_request http://lxr.linux.no/#linux+v3.1/block/blk-core.c#L1879 and blk_peek_request is getting invoked from scsi_request_fn http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c#L1493 scsi_request_fn is registered with the block layer as a request function at the following code http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c#L1688 And scsi_alloc_queue is invoked from scsi_alloc_sdev http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c#L238 scsi_alloc_sdev is invoked as a part of scsi lun discovery from lots of places http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c#L1004 http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c#L1306 The confusion I have is that the sd.c upper layer driver has not registered for a request function using blk_init_queue Any help would be appreciated. Thanks Sumeet

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When Are Free Pages Zeroed?
by Patrick Simmons Nov. 11, 2011

Nov. 11, 2011

I'm looking into the Linux memory management subsystem and need to know when freed pages are zeroed. Specifically, are they zeroed just before they are reallocated, immediately after they are freed, or sometime in-between? Also, what files/functions would I need to modify to change this behavior? Thanks for any help and kindest regards, --Patrick -- If I'm not here, I've gone out to find myself. If I get back before I return, please keep me here.

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why tasklet cant sleep
by santhosh kumars Nov. 10, 2011

Nov. 10, 2011

hi, can any one please explain why tasklets cant sleep.softirqs and tasklets processing aided by the a set of per processor kernel threads(ksoftirqd) so it means tasklets/softirqs run in process context. it means tasklet can sleep right? thanks, karunakar.

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Char device initialization
by Daniel Hilst Selli Nov. 9, 2011

Nov. 9, 2011

I'm trying to create a example char device. The example compiles fine, but when I try to "cat" I got "No such device or address". I have reviewed the code thousend times and can't see what I'm missing Here is the code -> http://pastebin.com/Td03U0fK The read method is not good, I know, but is never called. I use my own running kenrel to test, I know that is danger. I'm building a qemu enviroment to test this better. Here is uname -a: Linux archlinux 3.0-ARCH #1 SMP PREEMPT Fri Oct 7 11:35:34 CEST 2011 x86_64 Intel(R) Core(TM) i3 CPU M 370 @ 2.40GHz GenuineIntel GNU/Linux Any idea? Thanks

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Re: Getting a block from a block device?
by Dan Luedtke Nov. 9, 2011

Nov. 9, 2011

Hallo, On Tue, Nov 8, 2011 at 12:27 PM, Stephen Gream <poisonthemon(a)gmail.com> wrote: > Once you have the device registered (on /sys or /dev), register a read > callback on the file and use copy_to_user to output the data I read that article you referred to, but I don't think it addresses my problem, as I may have been more clear on what I want to achieve before. Sorry for that! I want to eventually implement a file system, and therefore I am studying the kernel sources to get an idea about all that. Here is my general understanding on how thinks may work :) virtual file system (VFS) <-[1]-> my file system implementation <-[2]-> a block device As I understood, all these subsystems are running in kernel mode. For [1] I read vfs.txt and learned about the VFS-API For [2] I have no idea where I can find the API documentation, however there were some hints on the book "Linux Driver Development" from O'Reilly in chapter "block devices". Nothing really helpful, as they were talking about registering new block devices. I want to use already present devices where I expect my filesystem to be present on. To check that, I have to read the first 512 bytes. The userspace implementation I was talking about previously is something like a mkfs.myfilesystem, that's why i referred to fopen() there. Thank you! Greetings, Dan -- Dan Luedtke http://www.danrl.de

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Mailing list for 802.15.4
by Prajosh Premdas Nov. 9, 2011

Nov. 9, 2011

Hi Is there any separate mailing list for 802.15.4 stack drivers?(Address family and drivers) I was goggling across and did not see any of them. Could anybody please update me. -- Regards, Prajosh Premdas

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building linux kernel 3.0.4
by ashish anand Nov. 8, 2011

Nov. 8, 2011

Hi , I am using vmware on windows 7 and try to built kernel version 3.0.4 . I am following this procedure make defconfig make make modules make modules_install make install Every step succeds except make install Its throwing me following message *sh /home/ashu/linux-3.0.4/linux-3.0.4/arch/x86/boot/install.sh 3.0.4 arch/x86/boot/bzImage \ System.map "/boot" ERROR: modinfo: could not find module fuse ERROR: modinfo: could not find module sunrpc ERROR: modinfo: could not find module ip6t_REJECT ERROR: modinfo: could not find module nf_conntrack_ipv6 ERROR: modinfo: could not find module ip6table_filter ERROR: modinfo: could not find module ip6_tables ERROR: modinfo: could not find module ipv6 ERROR: modinfo: could not find module uinput ERROR: modinfo: could not find module snd_ens1371 ERROR: modinfo: could not find module gameport ERROR: modinfo: could not find module snd_rawmidi ERROR: modinfo: could not find module snd_ac97_codec ERROR: modinfo: could not find module ac97_bus ERROR: modinfo: could not find module snd_seq ERROR: modinfo: could not find module snd_seq_device ERROR: modinfo: could not find module snd_pcm ERROR: modinfo: could not find module ppdev ERROR: modinfo: could not find module snd_timer ERROR: modinfo: could not find module parport_pc ERROR: modinfo: could not find module snd ERROR: modinfo: could not find module parport ERROR: modinfo: could not find module microcode ERROR: modinfo: could not find module soundcore ERROR: modinfo: could not find module vmware_balloon ERROR: modinfo: could not find module snd_page_alloc ERROR: modinfo: could not find module pcnet32 ERROR: modinfo: could not find module mii ERROR: modinfo: could not find module i2c_piix4 ERROR: modinfo: could not find module i2c_core ERROR: modinfo: could not find module mptspi ERROR: modinfo: could not find module mptscsih ERROR: modinfo: could not find module mptbase ERROR: modinfo: could not find module scsi_transport_spi *I wonder if my Vmware workstation is creating a problem? Or If I am using make defconfig why are these modules not bulit. Please help I am stuck. Thanks and Regards Ashish Anand "Growth Should Not Kill Innovation"

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Getting a block from a block device?
by Dan Luedtke Nov. 8, 2011

Nov. 8, 2011

Hallo everyone, could someone please give me a hint on how to get a block (e.g. 512 bytes) from a block device from a kernel module? What .txt should I consult? Which headerfiles must I include? Where can I find the required function's definitions? In userspace I used fopen() with the device path as filename, I bet it isn't that easy in kernel mode. I am using kernel sources from gentoo: 3.0.6-gentoo, but I can use vanilla if it really helps. thanks, Dan -- Dan Luedtke http://www.danrl.de

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Re: some questions about block and scatterlist
by loody Nov. 7, 2011

Nov. 7, 2011

Dear Jonathan: 2011/11/1 Jonathan Corbet <corbet(a)lwn.net>: > On Tue, 1 Nov 2011 19:32:38 +0900 > loody <miloody(a)gmail.com> wrote: > >> My questions are below: > > As are some answers :) That will be great appreciated :) > >> 1. Are all struct page 32-bit aligned? > > Certainly, I would expect any structures found in the system memory map to > be so aligned, yes. If you've created an arbitrary one elsewhere I'm only > 99% sure it would be. > >> If so, where is this part of code for handleing struct page be 32-bits aligned? > > Note that the size of struct page is carefully considered, and that they > are packed as densely as possible, both externally and internally. No > lesser alignment would make sense. I found kernel stealing LSB of page_link to put additional information, such as sg_is_chain and sg_is_last. That means the address of all pages have to be at least 4byte alignment. But I didn't see any additional attribute added at the end of struct or any precaution to take care this. > >> 2. if the page of scatterlist is located at high mem, how does >> dma_map_sg mapping the virtual address? > > That depends on a vast array of things. What are the addressing > capabilities of the target device? Is there an IOMMU involved? No, my device has no iommu. and I found where kernel handle this part. > >> 3. in blk_rq_map_sg, it seems we only copy bvec->bv_page to sg->page_link >> why don't we add dma_address in bvec and send the bio directly to >> the lower level driver? > > That would be a bit of a mixing of the layers, if nothing else. > >> 4. if I plug a USB HD with 3 partitions, will there be 3 request_queues? > > No, there is one request queue for the underlying device. I study some block devices and it seems we use blk_init_queue for getting a request_queue, if we want block layer handle requests and coalesces adjacent requests. what happen and lower driver need to do if we don't use blk_init_queue to register a request_queue? > > That's an interesting mix of questions. If you have more in the future, > you'll likely get more (and more clueful) responses if they're accompanied > by the code you're working on. > > Thanks, > > jon -- Regards,

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Contributing for the first time
by Alexandru Juncu Nov. 7, 2011

Nov. 7, 2011

Hello! I have been a linux user for many years, and mostly on the networking side. And I would like to start contributing somehow to the linux community (in some other way than just promoting it). I guess that I should start small with something like man pages. And there is something that really has been bugging me for some time. I'm an iproute2 user and I teach linux courses and show people how to use it. On most questions from my students about new commands, I redirect them to the man pages and to the Examples section of that page. iproute2 doesn't have such examples and I always wish it did. Do you think that if I submit a patch to the man pages, adding some examples of how to use the ip command, will it get accepted? Because this sounds like a simple thing and it's hard to believe that someone else didn't try do to this before. What do you think? -- Alexandru Juncu

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