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

notifier chains
by PV Juliet July 31, 2013

July 31, 2013

Hi All, Is there some mechanism for device drivers in the kernel to get the output to send to /proc filesystem (eg .registered event handlers output of notifier chains to proc file)? Thanks and Regards Juliet

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Getting Started
by Karan Dev July 30, 2013

July 30, 2013

hey, I am new here. I'd like to contribute to your organisation. Could someone guide me along ?

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Section Mismatch error
by Vignesh Radhakrishnan July 30, 2013

July 30, 2013

Hi, I am facing the following error when i am building the kernel. ERROR: modpost: Found 2 section mismatch(es). To see full details build your kernel with: 'make CONFIG_DEBUG_SECTION_MISMATCH=y' To build the kernel despite the mismatches, build with: 'make CONFIG_NO_ERROR_ON_MISMATCH=y' (NOTE: This is not recommended) make[3]: *** [__modpost] Error 1 make[2]: *** [modules] Error 2 make[1]: *** [sub-make] Error 2 After i did make the kernel using make CONFIG_DEBUG_SECTION_MISMATCH=y it said *section mismatch .* I am trying to write a platform driver (not sure if my code is right ) #include<linux/spinlock.h> #include <linux/module.h> /* Needed by all modules */ #include <linux/kernel.h> #include <asm/io.h> /* Needed for KERN_INFO */ #include <linux/platform_device.h> MODULE_LICENSE ("GPL"); static int __devinit my_module_probe(struct platform_device *pdev){ printk(KERN_INFO "Probe\n"); return 0; } static int __devexit my_module_remove (struct platform_device *pdev) { printk(KERN_INFO "Goodbye world 1.\n"); return 0; } static struct of_device_id spinlock_match[] = { {.compatible = "spinlockcrash"}, {} }; static struct platform_driver spinlock_platformdev = { .probe = my_module_probe, .remove = __devexit_p(my_module_remove), .driver = { .name = "spinlock_platformdev", .owner = THIS_MODULE, .of_match_table = spinlock_match, }, }; static int __init mymodule_init(void) { printk(KERN_INFO "INIT"); platform_driver_register(&spinlock_platformdev); return 0; } static void __exit mymodule_exit(void) { printk(KERN_INFO "GOOD BYE"); platform_driver_unregister(&spinlock_platformdev); } module_init(mymodule_init); module_exit(mymodule_exit); Can anybody throw some light on what might be happening here ? Thanks and regards, Vignesh -- http://vigneshradhakrishnan.blogspot.com/

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(no subject)
by PV Juliet July 30, 2013

July 30, 2013

HI , I am new to kernel . I got some stuff on notifier chains from net. Where i can more elaborated documents on notifier chains ? Can i get the module out put to user space(eg usb disk added) ? I don't want to get it from dmesg. Thanks and Regards Juliet

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Which repo should I clone?
by Dolan Murvihill July 30, 2013

July 30, 2013

Hello, I've been able to figure out from all the various HOWTOs about the different kernel trees (main development, -next, -stable, the subsystem trees, etc.) and I see where the files and patches are archived on kernel.org, but I haven't been able to find the actual git repos that I need to clone to work on the main kernel, or any of the others. Can someone please elaborate on exactly where each of these are stored so that I can more easily translate this conceptual knowledge into the actual git commands I have to run to make it work? Thanks, Dolan

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Why use "." in the struct in this way?
by lx July 29, 2013

July 29, 2013

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Notifier Chains
by PV Juliet July 29, 2013

July 29, 2013

Hi, Is there any way to add a new chain to notifier chain?? One more thing whatever the events i am register/unregister the output i am able to get in dmesg using printk. Can i get these output to userspace (eg files) Thanks a lot Juliet

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Direct IO and Page cache
by Kumar amit mehta July 26, 2013

July 26, 2013

Hi, We have direct I/O(O_DIRECT), for example raw devices(/dev/rawctl) that map to the block devices and we also have page cache. Now If I've understood this correctly, direct I/O will bypass this page cache, which is fine, I'll not get into the performance debate, but what about data consistency. Kernel cannot and __should'nt__ try to control how the applications are being written. So one bad day somebody comes up with an application which does both these two types of IO(one that goes through page cache and the other that doesn't) and in that application, one instance is writing directly to the backend device and the other instance, who is not aware of this write, goes ahead and writes to the page cache, and that write would be written later to the backend device. So wouldn't we end up corrupting the on disk data. I can think of multiple other scenarios which could corrupt the on-disk data, if there isn't any safeguarding policies employed by the kernel. But I'm very much sure that kernel is aware of such nasty attempts, and I'd like to know how does kernel takes care of this. !!amit

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Issue with copy_from_user() function in kernel 3.6.10
by Sateesh Kumar July 26, 2013

July 26, 2013

Dear Experts, I am using the kernel 3.6.10 for my driver development. When I compiled the code I am getting the following warning. I am facing the same issue with 3.5.4 kernel. "call to ‘copy_from_user_overflow’ declared with attribute warning: copy_from_user() buffer size is not provably correct" When I try to install the module, I am facing the kernel crash. Here is the crash log. //Kernel crash log - Start Call Trace: [19592.491229] [<c044bbf2>] warn_slowpath_common+0x72/0xa0 [19592.491233] [<c06882b7>] ? copy_from_user_overflow+0x27/0x30 [19592.491236] [<c06882b7>] ? copy_from_user_overflow+0x27/0x30 [19592.491241] [<f86f54c0>] ? jtag_usb_card_read+0x70/0x70 [usb_jtag] [19592.491244] [<c044bcc3>] warn_slowpath_fmt+0x33/0x40 [19592.491247] [<c06882b7>] copy_from_user_overflow+0x27/0x30 [19592.491251] [<f86f54ec>] jtag_usb_ioctl+0x2c/0x80 [usb_jtag] [19592.491256] [<c0565dea>] do_vfs_ioctl+0x7a/0x590 [19592.491259] [<c055f41b>] ? putname+0x2b/0x40 [19592.491262] [<c055f41b>] ? putname+0x2b/0x40 [19592.491265] [<c0555238>] ? do_sys_open+0x158/0x1c0 [19592.491269] [<c0566368>] sys_ioctl+0x68/0x80 [19592.491274] [<c0980cdf>] sysenter_do_call+0x12/0x28 [19592.491276] ---[ end trace 98bdb358664246ac ]--- [19592.491277] copy_from_usr error //Kernel crash log - End Please let me know, what wrong with my driver? Thanks in advance, Regards, Sateesh

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mmap how does kernel know a page is mmaped
by kernel neophyte July 26, 2013

July 26, 2013

Hi, Could anyone please explain, how mmap works underneath ? when kernel traveses pgd->pud->pmd->pte how does it know that a particular page is a mmaped page ? is there any special flag ? Thanks, Neophyte

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