December 2014 - kernelnewbies@kernelnewbies.org

The limits of move operation in shared-subtree
by Rock Lee Dec. 8, 2014

Dec. 8, 2014

Hi, all: I am reading the implementation of shared-subtree in linux kernel. There are two limits about move operation confused me badly, I have read the design document -- Shared-Subtree Concept, Implementation, andApplications in Linux ,but still puzzled. 1.Why can't move a mount residing in a shared mounts?2.Why can't move a mount tree containing an unbindable mount to a shared mount?Is it not a good way to prune out unbindable mounts just like rbind semantics do? Thanks in advanceRock Lee--------------------------------

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lkml archive
by John de la Garza Dec. 6, 2014

Dec. 6, 2014

I'm trying to catch up on a thread here: https://lkml.org/lkml/2014/10/29/854 does anyone here use lkml.org to read kernel mailing list archives? If so, how does the threading on the left work? I click on a link then the whole list shrinks. I have noticed that somethings are not visible at the top 'first message in thread' link. example smaller list: https://lkml.org/lkml/2014/10/30/124 I'f I count all the lines at the top first post level and go to another website with an interface that shows all the threads, I see a difference of about 25 in the count. So I'm thinking somethings are hidden at the top level. I have found another archive that is easy for me to read, but I am just curious to what I am missing and why the lkml.org site's behavior surprises me. I must be missing something obvious. My goal was to simply read the the entire thread.

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the cost of inlining?
by Jeff Haran Dec. 6, 2014

Dec. 6, 2014

Hoping this isn't too far off the topic, but I figure it might be of interest to other kernel developers and it has me a bit baffled. The primary benefit to inlining functions is to avoid the cost of making function calls. At least that's how I've understood it. So I was playing with a bit of sample code: $ cat atomic_read.c #include <asm/atomic.h> #include <asm/system.h> int samp_atomic_read(atomic_t *v) { int val; val = atomic_read(v); return val; } atomic_read() is declared like so: static inline int atomic_read(const atomic_t *v) { return v->counter; } So I figured the compilation of the my sample code would result in no call to a function with samp_atomic_read(). But after I build the above with the following Makefile: $ cat Makefile obj-m += atomic_read.o all: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean I dump the resultant .ko, I get this: > objdump -S -M intel atomic_read.ko atomic_read.ko: file format elf64-x86-64 Disassembly of section .text: 0000000000000000 <samp_atomic_read>: #include <asm/atomic.h> #include <asm/system.h> int samp_atomic_read(atomic_t *v) { 0: 55 push rbp 1: 48 89 e5 mov rbp,rsp 4: e8 00 00 00 00 call 9 <samp_atomic_read+0x9> * * Atomically reads the value of @v. */ static inline int atomic_read(const atomic_t *v) { return v->counter; 9: 8b 07 mov eax,DWORD PTR [rdi] int val; val = atomic_read(v); return val; } b: c9 leave c: c3 ret d: 90 nop e: 90 nop f: 90 nop I think I understand most of it. The first 2 instructions save the base pointer of the caller and setup a new one from samp_atomic_read(). The instruction at offset 9 reads the contents of v->counter into eax to return to the caller. The instruction at offset 0xb, restores the base pointer and stack pointer of the caller and the ret at offset 0xc returns execution to the caller. I am guessing the nops at the end are to make the next function land on an 8 byte boundary (this is for an X86_64 target). But what is that call instruction at offset 4 for? It would seem to accomplish nothing since without it execution would proceed at the mov at offset 9 like I'd expect and since no new base frame gets setup inside atomic_read() itself, the leave/ret causes control to return to the caller of samp_atomic_read() anyway. If atomic_read() were a macro, we wouldn't have this seemingly superfluous call instruction. Anybody know why it's there? Thanks, Jeff Haran

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[Eudyptula] How long have you been waiting?
by karthik nayak Dec. 5, 2014

Dec. 5, 2014

Hello, As patient as I am, just wondering how long have you all been waiting for your response. I'm waiting for quite a while now on the 8th task. Regards, Karthik Nayak

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x86/kernel/head_32.S
by 孙建希 Dec. 5, 2014

Dec. 5, 2014

hello, arch/x86/kernel/head_32.S: #define pa(X) ((X) - __PAGE_OFFSET) __HEAD ENTRY(startup_32) + movl pa(stack_start),%ecx... + movl %eax,%ss 2: + leal -__PAGE_OFFSET(%ecx),%esp I am confused by `leal -__PAGE_OFFSET(%ecx),%esp`. `pa(stack_start)` have convert `stack_start` to physicall address. why we need `-__PAGE_OFFSET(%ecx)` instead of `%ecx`? I have found the commit in github: https://github.com/torvalds/linux/commit/11d4c3f9b671720e80353dd7e433ff2bf6…

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Problem in Getting Mainline Kernel
by Freeman Zhang Dec. 5, 2014

Dec. 5, 2014

Hi list, I cloned it for nearly 30 hours due to the poor connection :( How I wish the cloning process is resumable. Finally I cloned the mainline kernel from "git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git". However, when I'm looking at the git directory, I got nothing but: . .. arch .DS_Store .git .gitignore .mailmap I'm confused. I thought it would be like this: arch include mm security block init modules.builtin sound COPYING ipc modules.order System.map CREDITS Kbuild Module.symvers tools crypto Kconfig net usr Documentation kernel README virt drivers lib REPORTING-BUGS vmlinux firmware MAINTAINERS samples vmlinux.o fs Makefile scripts Is my clone broken? I ran `git pull` and it said the clone is up-to-date. And the size of .git directory is over 1 GB. Now I'm using `tar.xz` from kernel.org and it works just fine. But I still want to know what I should do with my git clone. All the best! Freeman Zhang

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stability ?
by libin Dec. 4, 2014

Dec. 4, 2014

hello， Does anybody know what test should do before a patch added into the kernel ? I am interested in the method to prove the stability and performance of kernel , especially the stability . can anybody help me ? thanks very much ! icelee

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Re: Kernelnewbies Digest, Vol 49, Issue 7
by libin Dec. 4, 2014

Dec. 4, 2014

hello， Does anybody know what test should do before a patch added into the kernel ? I am interested in the method to prove the stability and performance of kernel , especially the stability . can anybody help me ? thanks very much ! icelee

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[RESOLVED] Help! - fuse and loopback - not working together
by Greg Freemyer Dec. 4, 2014

Dec. 4, 2014

The issue is that I was running the fuse mount command as a normal user and mount as root. By default fuse does NOT allow root to access filesystems it creates unless root created them. For me there are 2 work-arounds: - Add sudo in front of my command creating the filesytem - Set an option in /etc/fuse.conf to allow none-owners of a filesystem to use the filesystem. I suspect when I did this in the past I was running as root, so I never noticed the problem. Sorry for the noise, Greg -- Greg Freemyer On Wed, Dec 3, 2014 at 7:12 PM, Greg Freemyer <greg.freemyer(a)gmail.com> wrote: > All, > > I don't know if this is a kernel issue or not. I just don't know > where else to look for help. > > I seem to be having a conflict between fuse and loopback devices. I > can get each to work fine independently, but I can get them to work > together. This has worked with older kernels, but I can't get it to > work with a 3.16.6 kernel. > > I'm just guessing the issue is a kernel issue. I really don't want to > have to compile kernels to track this down, but it may come to that. > > All userspace tools I'm using are opensource, so I dod have the > userspace source to work with, although I'm not the author. > > ===== > I'm trying to use a tool (ewfmount) that leverages the fuse kernel > sub-system to merge several files together and also uncompress them. > > Thus I might originally have: > > image.E01 > image.E02 > image.E03 > > where each of those files is a segment of full dd image that has been > compressed. > > If I run "ewfmount image.E01 /mnt" then a virtual file /mnt/ewf1 is > created. That is working fine. > > In the past I have been able to now loopback mount partitions from > that virtual file via: > > mount -t hfsplus -r -o loop,offset=209735680 /mnt/ewf1 /mnt > > Currently that is failing with: > mount: /mnt/ewf1: failed to setup loop device: Permission denied > > Thus loop back seems broken. To test that I copied the virtual file > to a real file via dd. After that mount properly accesses the true > file. > > === > Thus: > > fuse is working right to merge my files together and uncompress them. > > loopback is working right when the object being mounted is a standard file. > > loopback is failing when pointed at the virtual file created by fuse. > === > > I am suspicious of the kernel because this has worked for me in the > pastk but with older kernels. I can't say when it last worked, but at > least a year ago. > > Any suggestions / help appreciated. > > Thanks > Greg > -- > Greg Freemyer

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Help! - fuse and loopback - not working together
by Greg Freemyer Dec. 4, 2014

Dec. 4, 2014

All, I don't know if this is a kernel issue or not. I just don't know where else to look for help. I seem to be having a conflict between fuse and loopback devices. I can get each to work fine independently, but I can get them to work together. This has worked with older kernels, but I can't get it to work with a 3.16.6 kernel. I'm just guessing the issue is a kernel issue. I really don't want to have to compile kernels to track this down, but it may come to that. All userspace tools I'm using are opensource, so I dod have the userspace source to work with, although I'm not the author. ===== I'm trying to use a tool (ewfmount) that leverages the fuse kernel sub-system to merge several files together and also uncompress them. Thus I might originally have: image.E01 image.E02 image.E03 where each of those files is a segment of full dd image that has been compressed. If I run "ewfmount image.E01 /mnt" then a virtual file /mnt/ewf1 is created. That is working fine. In the past I have been able to now loopback mount partitions from that virtual file via: mount -t hfsplus -r -o loop,offset=209735680 /mnt/ewf1 /mnt Currently that is failing with: mount: /mnt/ewf1: failed to setup loop device: Permission denied Thus loop back seems broken. To test that I copied the virtual file to a real file via dd. After that mount properly accesses the true file. === Thus: fuse is working right to merge my files together and uncompress them. loopback is working right when the object being mounted is a standard file. loopback is failing when pointed at the virtual file created by fuse. === I am suspicious of the kernel because this has worked for me in the pastk but with older kernels. I can't say when it last worked, but at least a year ago. Any suggestions / help appreciated. Thanks Greg -- Greg Freemyer

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