February 2012 - kernelnewbies@kernelnewbies.org

arm assembly doubt
by subin gangadharan Feb. 18, 2012

Feb. 18, 2012

Hi , I am trying to understand how system call is implmented in linux for arm.And I am not that familiar with arm assembly. Could any body please help me to understand what exactly this ^ does in this instruction stmdb r8,{sp,lr}^ -- With Regards Subin Gangadharan I am not afraid and I am also not afraid of being afraid.

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Contribute to linux camera drivers
by Mayank Agarwal Feb. 18, 2012

Feb. 18, 2012

Hi all, I want to contribute to linux device driver development in the field of camera/image/audio video. Please help me to get into this. Thanks and Regards, Mayank

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softirq argument
by srimugunthan dhandapani Feb. 16, 2012

Feb. 16, 2012

Hi all As an experiment, i am trying to use softirq instead of using tasklet in my driver code. I was passing the driver's structure pointer to the tasklet. The "open_softirq" takes only the function pointer as argument. Since we can't pass any argument to the softirq, is there any workaround that is possible to make the structure pointer accessible to softirq? I just need to do this for taking measurements. Thanks, mugunthan

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Dual booting of Smartphone
by Abhijit Pawar Feb. 16, 2012

Feb. 16, 2012

Hi All, I know its pre-mature to ask this question but is there any support of dual booting in smartphones which can allow me have two different OS's ( for ex. Android 2.1 + Android 2.3 ) on a single phone? There may be other combinations as well. Is this something which we are looking at near future or is it just a dream at this moment? Regards, Abhijit Pawar

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[QUESTION] staging/easycap fix
by Ezequiel García Feb. 16, 2012

Feb. 16, 2012

Hi, I'm try to fix staging/easycap driver. I know it has some bugs somewhere (I've seen some panics while using the device) but I wanted to improve the code style before debugging it. In the meantime, I expect to develop a better understanding of the code. However, I want know if I am in the right direction; so I want to know if this is ok: 1. mainly I am splitting very large functions into smaller parts. For instance, xxx_probe function is +1k lines long, so I'm splitting it up to make the code cleaner, more readable. Is this ok? 2. second, I am fixing some style issues (besides checkpatch), for instance "if" syntax: - if (0 == bInterfaceNumber) { + if (bInterfaceNumber == 0) { and ugly comments like: -/*---------------------------------------------------------------------------*/ -/* - * GET PROPERTIES OF PROBED INTERFACE - */ -/*---------------------------------------------------------------------------*/ + + /* + * GET PROPERTIES OF PROBED INTERFACE + */ So, Am I on the right track? Thanks, Ezequiel.

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A problem with percpu variable cpu_number
by tao jiang Feb. 16, 2012

Feb. 16, 2012

Hi : At the beginning of start_kernel() -- init/main.c boot_cpu_init() is called and in boot_cpu_init() will call smp_processor_id() it's a macro and it will be expanded as (percpu_read(cpu_number)) and so on but i noticed that it's before setup_per_cpu_areas() in start_kernel() is that mean the percpu areas hadn't be initialized yet but why smp_processor_id() could be called before setup_per_cpu_areas() Thank you. --------------- jiangtao

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Using Sysfs uevents.
by Pranay Kumar Srivastava Feb. 15, 2012

Feb. 15, 2012

Hi, I was playing with sysfs and I'm able to create kset and kobjects within them as well. I need to know how do I use the uevents of these kobjects that I create. For example while reading the code I found that certain events like ADD, DEL a couple more were there are apparently fired. Now currently I'm not handling these events, the ops field is null, so they don't bother me hence they are not mandatory? If I were to actually do something with these events what it should be? Since my module runs fine and the uevents are supposed to be for userland applications (Hotplug) but the point is again how will a userspace application get to know about it? Does the application needs to create netlink sockets for it? If it does then why bother with the uevents of kobject? ::DISCLAIMER:: ----------------------------------------------------------------------------------------------------------------------- The contents of this e-mail and any attachment(s) are confidential and intended for the named recipient(s) only. It shall not attach any liability on the originator or HCL or its affiliates. Any views or opinions presented in this email are solely those of the author and may not necessarily reflect the opinions of HCL or its affiliates. Any form of reproduction, dissemination, copying, disclosure, modification, distribution and / or publication of this message without the prior written consent of the author of this e-mail is strictly prohibited. If you have received this email in error please delete it and notify the sender immediately. Before opening any mail and attachments please check them for viruses and defect. -----------------------------------------------------------------------------------------------------------------------

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System call trace
by Swapnil Gaikwad Feb. 15, 2012

Feb. 15, 2012

Can we see trace of how the system call works? What are the functions are called in kernel space? For example we want to trace cp command. Then what are the functions is get called by that in kernel space? like how the inode allocation take place for new destination file etc. Is any tool for that? -- Regards, Swapnil Gaikwad.

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Re: Does unmount() sync dirty buffers
by Manish Katiyar Feb. 15, 2012

Feb. 15, 2012

[Apparently I forgot to cc list] On Tue, Feb 14, 2012 at 10:04 PM, Manish Katiyar <mkatiyar(a)gmail.com> wrote: > On Tue, Feb 14, 2012 at 7:43 PM, Ravishankar <cyberax82(a)gmail.com> wrote: >> Hello, >> >> When we unmount a file system with the umount command or the umount() system >> call, does the kernel sync the dirty buffers before the file system is >> unmounted?I am assuming that the file system is not 'busy' (i.e no open >> files etc) and no force options are specified. When I did a walk-through of >> do_umount() call in fs/namespace.c, I could not find calls to sync any dirty >> pages that might exist. > > yes, most of the filesystem have their own function to sync fs. Look > for the function pointer "sync_fs" > > For eg..for ext4 > > generic_shutdown_super -> sync_filesystem -> __sync_filesystem -> > sync_fs -> ext4_sync_fs > -- > Thanks - > Manish -- Thanks - Manish

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Does unmount() sync dirty buffers
by Ravishankar Feb. 15, 2012

Feb. 15, 2012

Hello, When we unmount a file system with the umount command or the umount() system call, does the kernel sync the dirty buffers before the file system is unmounted?I am assuming that the file system is not 'busy' (i.e no open files etc) and no force options are specified. When I did a walk-through of do_umount() call in fs/namespace.c, I could not find calls to sync any dirty pages that might exist. Thanks! Ravi

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