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why are some stat.h "S_*" perm macros not exported via uapi?
by Robert P. J. Day Jan. 1, 2019

Jan. 1, 2019

more pedantry ... just noticed this snippet in include/linux/stat.h: ... #include <uapi/linux/stat.h> #define S_IRWXUGO (S_IRWXU|S_IRWXG|S_IRWXO) #define S_IALLUGO (S_ISUID|S_ISGID|S_ISVTX|S_IRWXUGO) #define S_IRUGO (S_IRUSR|S_IRGRP|S_IROTH) #define S_IWUGO (S_IWUSR|S_IWGRP|S_IWOTH) #define S_IXUGO (S_IXUSR|S_IXGRP|S_IXOTH) ... given that all of the other S_ perm macros are exported in include/uapi/linux/stat.h, as in: #define S_IRWXU 00700 #define S_IRUSR 00400 #define S_IWUSR 00200 #define S_IXUSR 00100 #define S_IRWXG 00070 #define S_IRGRP 00040 #define S_IWGRP 00020 #define S_IXGRP 00010 and so on, is there a reason those few combination perm macros are not exported as well? or is the userspace stat.h so well-defined at this point that cosmetic changes like this are frowned upon? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca/dokuwiki Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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stylistically, IS_ERR() versus IS_ERR_VALUE()?
by Robert P. J. Day Dec. 31, 2018

Dec. 31, 2018

poking around error handling in the kernel, and noticed the following ... in include/linux/err.h, we have IS_ERR() unsurprisingly defined in terms of IS_ERR_VALUE(): #define IS_ERR_VALUE(x) unlikely((unsigned long)(void *)(x) >= \ (unsigned long)-MAX_ERRNO) ... snip ... static inline bool __must_check IS_ERR(__force const void *ptr) { return IS_ERR_VALUE((unsigned long)ptr); } fair enough, and the above suggests that it's technically equivalent to use either one, but if i search under drivers/ for each: $ git grep -w IS_ERR -- drivers | wc -l 14048 $ $ git grep -w IS_ERR_VALUE -- drivers | wc -l 48 $ so IS_ERR() is pretty clearly the call of choice, and the invocations of IS_ERR_VALUE() are concentrated in a small number of files -- heck, 15 of those calls are in the single file drivers/net/ethernet/freescale/ucc_geth.c. is there any non-obvious reason for driver code to use the latter? superficially, they *seem* to be equivalent, but i've been surprised before. rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca/dokuwiki Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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Listing Supported Kernel Parameters?
by Henry C Dec. 31, 2018

Dec. 31, 2018

Hi, I am looking for a command (or alike) to list all the supported kernel parameters based on my current kernel. If such command doesn't exist, it would still be great to see a complete list like this one: https://www.kernel.org/doc/html/v4.15/admin-guide/kernel-parameters.html But I can't find anything (reliable) for v3.10. Thanks.

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8 bytes reserved at the top of the stack in arm
by ksourav Dec. 28, 2018

Dec. 28, 2018

Hi, In arm linux, kernel stack is 8KB(two consecutive pages). struct pt_regs lie at the top of the stack and thread_info lie at the bottom of the stack. In arch/arm/include/asm/processor.h #define task_pt_regs(p) \ ((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1) In arch/arm/include/asm/threadinfo.h #define THREAD_START_SP (THREAD_SIZE - 8) Why are 8 bytes reserved at the top ? Also, seeing similar thing in arch/arm/include/asm/ptrace.h #define current_pt_regs(void) ({ (struct pt_regs *) \ ((current_stack_pointer | (THREAD_SIZE - 1)) - 7) - 1; \ }) (current_stack_pointer | (THREAD_SIZE - 1) It will get the top of stack and the we are subtracting 7 from it ? Why are these bytes reserved ? Thanks & Regards

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In a process context kernel_read returns -EINTR, how to proceed?
by Lev Olshvang Dec. 23, 2018

Dec. 23, 2018

Hi All, I use kernel_read to read file in chunks of 4K size in a process context On several files, like libc, libm, I got -EINTR error. Then I repeated the attempt limited number of times but still on every read attempt I got -EINTR I do not understand who may interrupt such a small read, I suppose these libraries are already mapped in other processes so no real I/O should be done. In a user space it is recommended to repeat syscall, what is the proper course of action in kernel. As I stated, this code is not in a kernel thread or atomic context, it is in a process context so a tried before next attempt yield() but to no success. Waiting for your advises. Thx, Lev

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How to detect slab memory leak
by Naruto Nguyen Dec. 21, 2018

Dec. 21, 2018

Hi everyone, When using slabtop to display the cache size growing, I see that kmalloc-1024 and kmalloc-256 are increasing about 200MB after 1 hour. Is there any way to detect which kernel components cause this slab increase? Thanks a lot, Brs, Naruto

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Dec. 20, 2018

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/proc/modules not showing any output
by Praveen Kumar Dec. 20, 2018

Dec. 20, 2018

Hi All, Compiled the vanila kernel 4.20.0-rc6 build, and was trying to get module information, but /proc/modules is not showing any output ( both on arm64 and x86_64 ) root@ubuntu:~# uname -a Linux ubuntu 4.20.0-rc6-00082-g65e08c5e8631 #7 SMP PREEMPT Fri Dec 14 15:54:30 IST 2018 aarch64 aarch64 aarch64 GNU/Linux root@ubuntu:~# cat /proc/modules root@ubuntu:~# Tried with older version 4.4.162-78-default modules were properly shown. Can you please help if there is something which I am missing during compilation or is there any potential bug here ? Thanks in advance. Regards, ~Praveen.

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a specific question...
by R. Engür Pişirici Dec. 17, 2018

Dec. 17, 2018

Hello All, Before starting to ask my question, I would like to apologize about asking a silly question. Mostly, i always try to find answers by reading, searching, digging, etc. However, i really couldnt find a proper answer for my question. My question is about l2tp/pptp drivers in kernel. pptp driver is in /drivers/net. But, l2tp driver is in /net I want to know why they reside in different paths? What did i miss? Best Regards, -engur

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[RFC] LKML Archive in Maildir Format
by Joey Pabalinas Dec. 16, 2018

Dec. 16, 2018

I spent a lot of time trying to find an LKML archive in Maildir format that I could use for local searches with nutmuch or something, but all the links I was able to find were all dead. I ended up just compiling one myself and I currently host it at: https://alyptik.org/lkml.tar.xz It's possible I'm the only weirdo who finds this kind of thing useful, but I figured I should share it just in case I'm not. It's about 1.1 million files, I was wondering if anyone had an idea of a better way to host this? I've tried Github and GitLab, but they don't appreciate repos with that many files, hah. Open to suggestions, thanks! -- Cheers, Joey Pabalinas

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