February 2013 - kernelnewbies@kernelnewbies.org

Re: kernel source code tree
by sunil Feb. 11, 2013

Feb. 11, 2013

Hi all, need help, I am trying to write simple device driver. But before that i need to download kernel source code tree someone please explain how to download this and configure. I am very new to this. I am using ubuntu 12.04 thanks & regards sunil A S

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printk question:why release console_sem after logbuf_lock
by buyitian Feb. 10, 2013

Feb. 10, 2013

in the patch 0b5e1c5255e7ee8670e077e8224e5c2281229a5b, it releases console_sem after logbuf_lock, the description of this patch is as below: Release console_sem after unlocking the logbuf_lock so that we don't generate wakeups while holding logbuf_lock. This avoids some lock inversion troubles once we remove the lockdep_off bits between logbuf_lock and rq->lock (prints while holding rq->lock vs doing wakeups while holding logbuf_lock).There's of course still an actual deadlock where the printk()s under rq->lock will issue a wakeup from the up() call, but lockdep won't warn about that since semaphores are not tracked. could you please give me a detail example about the issue it tries to fix? thanks.

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Kernel code interrupted by Timer
by Gaurav Jain Feb. 10, 2013

Feb. 10, 2013

What happens if the kernel executing in some process context (let's say executing a time-consuming syscall) gets interrupted by the Timer - which is apparently allowed in 2.6 onwards kernels. My understanding is that once the interrupt handler is done executing, we should switch back to where the kernel code was executing. Specifically, the interrupt handler for the Timer interrupt should not schedule some other task since that might leave kernel data in an inconsistent state - kernel didn't finish doing whatever it was doing when interrupted. So, does the Timer interrupt handler include such a policy for the above case? -- Gaurav Jain

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Re: MAX limit of file descriptor
by Gaurav Jain Feb. 9, 2013

Feb. 9, 2013

Reference: http://www.kernel.org/doc/man-pages/online/pages/man2/setrlimit.2.html On Sat, Feb 9, 2013 at 6:08 PM, Gaurav Jain <gjainroorkee(a)gmail.com> wrote: > I believe you can achieve the 'effect' of setting the maximum number of > open file descriptors to 'infinite' by using the following (untested code!): > > <snip> > #include <sys/time.h> > #include <sys/resource.h> > > struct rlimit rlim; > rlim.rlim_cur = RLIM_INFINTY; > rlim.rlim_max = RLIM_INFINITY; > > int ret = setrlimit(RLIMIT_NOFILE, &rlim); > </snip> > > Note that what Peter pointed out is more or less correct. You can't *actually > *have infinite file descriptors. The above code just ensures that the > kernel won't perform any checks on the number of open file descriptors. So, > if you hit a real resource limit; like no more memory left for opening > files, you would still get an error. My feeling is that this isn't a wise > thing to do. It's always better to know a precise number of the upper limit > rather than an arbitrarily large number. > > ~ Gaurav > > > On Sat, Feb 9, 2013 at 4:49 PM, Peter Teoh <htmldeveloper(a)gmail.com>wrote: > >> i can only make a general statement, may not be always true/false: >> >> in the kernel almost EVERYTHING HAS TO BE FINITE....and this is cater for >> the fact that >> >> but at the userspace or application level, u can design structures to be >> infinite. eg, I used python for large number calculation, and so far it >> has not limits, but I am sure at the representation level, there is >> one....but because i don't know the datastructure used, i don't know the >> limits. >> >> >> On Sat, Feb 9, 2013 at 1:10 PM, horseriver <horserivers(a)gmail.com> wrote: >> >>> hi:) >>> >>> In one process ,what is the max number of opening file descriptor ? >>> Can it be set to infinite ? >>> >>> In network programing ,what is the essential for the maximum of >>> connections >>> dealed per second >>> >>> thanks! >>> >>> _______________________________________________ >>> Kernelnewbies mailing list >>> Kernelnewbies(a)kernelnewbies.org >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>> >> >> >> >> -- >> Regards, >> Peter Teoh >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >> > > > -- > Gaurav Jain > Associate Software Engineer > VxVM Escalations Team, SAMG > Symantec Software India Pvt. Ltd. > > > -- Gaurav Jain Associate Software Engineer VxVM Escalations Team, SAMG Symantec Software India Pvt. Ltd.

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Can a bio have more sectors than a file system block size
by Prashant Shah Feb. 8, 2013

Feb. 8, 2013

Hi, In the make_request callback function is it possible for a bio to have bio_sectors() count more than the number of sectors in a file system block ? eg : If the disk sector size is 512 bytes and file system block size is 4096 bytes, I have only noticed bio_sectors() to be 8. Never seen anything more or less than 8. Regards.

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Fwd: register_console is getting stuck in acquire_console_sem()
by Ramesh Rajagopal Feb. 8, 2013

Feb. 8, 2013

---------- Forwarded message ---------- From: Ramesh Rajagopal <shmera(a)gmail.com> Date: Fri, Feb 8, 2013 at 5:12 PM Subject: register_console is getting stuck in acquire_console_sem() To: kernelnewbies(a)nl.linux.org, majordomo(a)vger.kernel.org I am working on 2.6.35.7-02894-g0482b09-dirty this kernel. I am trying to use g_serial as console(gadget serial). For that I am calling register_console() from gserial_setup() function. But this is getting stuck at acquire_console_sem(). When I printed semaphore count it is infact 1, but internally it is getting stuck at down() function spin lock(). Any idea what it could be ? I have patch which enables gserial as console. I want to get the kernel prints on USB port(don't have uart on our board). Regards, Ramesh.

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hd controller
by horseriver Feb. 8, 2013

Feb. 8, 2013

hi:) I am curious about how hd controller work . When user am reaing/writing hd ,it was implemented by sending command to hd controller's special port.Then ,how does the controller know a new command has received? In this procedure , what work does the hd driver do ? thanks!

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How the follow Starts in Android-Kernel
by Ranganath T.M Feb. 7, 2013

Feb. 7, 2013

Hi All, I am trying to find out how the kernel will *start* from the uboot and how the kernel will call there respective static modules which are built as *.o*file and also how the *probe* of every modules will be called. Thanks And Regards Ranganath

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pr_info not printing message in /var/log/messages
by Shraddha Kamat Feb. 7, 2013

Feb. 7, 2013

I was looking at http://stackoverflow.com/questions/8090944/printk-not-working-for-kernel-de… Initially it was - # cat /proc/sys/kernel/printk 7 4 1 7 Then i did - # echo "7 7" > /proc/sys/kernel/printk # cat /proc/sys/kernel/printk 7 7 1 7 # sysctl -a | grep printk kernel.printk = 7 7 1 7 kernel.printk_delay = 0 kernel.printk_ratelimit = 5 kernel.printk_ratelimit_burst = 10 still I the pr_info ("hello, world"); message doesn't get printed to /var/log/messages. please give me some hints as to resolve this issue. -- Shraddha

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Re: thread concurrent file operation
by Karaoui mohamed lamine Feb. 7, 2013

Feb. 7, 2013

Tahnks guys! 2013/1/30 Karaoui mohamed lamine <moharaka(a)gmail.com> > thanks, i think i get it. > > 2013/1/30 <Valdis.Kletnieks(a)vt.edu> > > On Tue, 29 Jan 2013 20:16:26 +0100, you said: >> >> > Actually my question is : >> > Does POSIX specifies the fact that we need to use "lockf" to be able >> to do >> > read/write operation in different offset ? Is'n the kernel supposed to >> > ensure this ? >> >> If you have non-overlapping writes, the kernel will eventually sort it out >> for you. If your writes overlap, you'll have to provide your own locking >> via lockf() or similar, and synchronization via other methods. >> > >

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