August 2018 - kernelnewbies@kernelnewbies.org

Difference between kernel logical address and kernel virtual address
by Abhinav Misra Aug. 19, 2018

Aug. 19, 2018

Hi, In LDD3 book at Ch-15 they mentioned all types of address used in the kernel. But wrt the book, not able to understand the difference between kernel logical and virtual address. Can somebody elaborate the same with some eg. BR,Abhinav

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System call vs POSIX call
by Subhashini Rao Beerisetty Aug. 17, 2018

Aug. 17, 2018

Hi All, I'm trying to get the difference between system call and POSIX call. System calls are user mode API's (open(), close(), ioctl(),...) gets the kernel service via software interrupt. What about POSIX calls and how it differs with the system call.? Can anyone clarify me on this.

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How to assess how much stack space kernel function may use?
by Lev Olshvang Aug. 16, 2018

Aug. 16, 2018

Hello all I am writing kernel module function that calls for vfs function , so I am not aware how deep kernel stack can grow due to my calls I need to take 512 bytes for some processing, and I know kernel stack is 4K only. My function is also part of calling chain, so I do not know how much stack is used before my function is called. What dara can I get from kernel during compilation and run about stack utiilizaton to help me in estimation ? Lev

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Is there any way to show local var when using crash to analyse coredump?
by Larry Aug. 16, 2018

Aug. 16, 2018

Hi list, When using gdb, we can use "frame" command to select which layer in the back trace to debug, and then we can use "print" command to print local var within this layer. But I found that these two commands does not work in crash tool, is there any way to solve it? Thanks Larry

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Proxy filesystems
by Demi Obenour Aug. 12, 2018

Aug. 12, 2018

How difficult would it be to create a proxy filesystem — that is, a filesystem that is a view of the filesystem? For instance, opening `/dev/urlfs/home/test/A%20Bcd` would open `/home/test/A Bcd`. The purpose would be to handle poorly written tools (like Autoconf and CMake) that do not handle wierd characters in filenames.

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A question on the function clean_bdev_bh_alias
by Larry Aug. 11, 2018

Aug. 11, 2018

Hello list, I'm confused with the function, could someone help?? Does it intend to remove existent pages in block device's page cache if some new page cache of a vfs file was created whose block number range has overlaps with its block device page cache? Thanks in advance. Best regards, Larry

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kobj->state_initialized is never set to 0
by Helen Koike Aug. 10, 2018

Aug. 10, 2018

Hi, I am simulating hotplugging a platform device (to the media/platform/vimc driver), so I register it using platform_device_register, then I unregister it with platform_device_unregister, then I register it again, but the code doesn't allow me to register something that was registered before due to this line: https://github.com/torvalds/linux/blob/master/lib/kobject.c#L334 The variable kobj->state_initialized is set to 1 at https://github.com/torvalds/linux/blob/master/lib/kobject.c#L194 but it is never set to 0 again. Is this how it is supposed to work? Or kobj->state_initialized is set to 0 somewhere else I couldn't find? Thanks Helen

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first patch question
by Greg Gallagher Aug. 10, 2018

Aug. 10, 2018

Hi, I creating my first patch to the kernel. I followed the instruction on the newbies wiki and everything went smoothly. I got feedback from the maintainer to fix all the alignment issues in the file instead of just the one i picked. My question is if I fix 10 alignment issues identified by checkpatch,pl should each fix be a separate commit? Should I have a 10 commit patch set for the 10 alignment issues or is it better to make them all one commit since all the commits are fixing alignment issues? Thanks for our time, Greg

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Virtual console devices
by Tushar Dave Aug. 6, 2018

Aug. 6, 2018

Hello, I am trying to optimize boot up time for my board. I ran bootchart and observed that virtual console devices are being created in very high number which finally cause the boot up time to increase by 1.5 seconds. I have been researching as to where these are actually being created and have failed to find anything concrete.Is there some way to reduce the count of virtual devices on the kernel side? Regards, Tushar

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Problem of compiling linux2.6.11.12 kernel
by He Huanyu Aug. 6, 2018

Aug. 6, 2018

Hi everyone, I try to compile linux kernel of 2.6.11.12 version on my 64bit archlinux. Below is my system information: linux 4.16.9-1-ARCH gcc (GCC) 8.1.1 20180531 GNU ld (GNU Binutils) 2.30 And I get a problem like this, don't know if it is because of the version of gcc or ld: /usr/bin/ld: arch/x86_64/ia32/vsyscall-sysenter.so: Not enough room for program headers, try linking with -N /usr/bin/ld: final link failed: Bad value collect2: error: ld returned 1 exit status make[1]: *** [arch/x86_64/ia32/Makefile:28: arch/x86_64/ia32/vsyscall-sysenter.so] Error 1 make: *** [Makefile:742: arch/x86_64/ia32] Error 2 I've tried to add ld parameter, but didn't know how and where to add this... Have you met this before? And how can I fix it?

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