January 2015 - kernelnewbies@kernelnewbies.org

Eudyptula Challenge response submission
by Alisha Jain Jan. 31, 2015

Jan. 31, 2015

Hello I am a newbie in the world of Linux Kernel. So I started Eudyptula Challenge. I have completed the patch along with the Makefile and it is being loaded successfully on my system. But I am stuck on how to send my response through mail. I am trying it from last two days, but didn't succeed. I am using Alpine web-client. Please guide me for it. -- Alisha Jain blog - jainalisha14.wordpress.com "Your Failure does not define you, but your determination does."

3 2

spinlock variable protection
by Matwey V. Kornilov Jan. 31, 2015

Jan. 31, 2015

Hi, I have the following code int ret = 0; unsigned long irqflags; spin_lock_irqsave(&lock, irqflags); //... ret = hdl->count; //... spin_unlock_irqrestore(&lock, irqflags); return ret; I would like to be sure, that ret will not be optimized out. I think compiler can convert the code to equivalent: unsigned long irqflags; spin_lock_irqsave(&lock, irqflags); //... //... spin_unlock_irqrestore(&lock, irqflags); return hdl->count; But this is not what I want, because I use lock to protect hdl and want to return hdl->count value as it was in protected section.

5 5

Linux Kernel readlink equivalent
by David Legault Jan. 30, 2015

Jan. 30, 2015

Hello, I'm working on some linux kernel driver stuff and I have a fake path called /dev/blah/whatever that points to /dev/block/real_device. The issue is that lookup_bdev will fail to follow the symlink so I'd like to massage the path upfront by getting the real path (/dev/block/real_device) so I can hand that off to lookup_bdev so it returns successfully instead of an error. Or any other kernel call that would correctly retrieve the block_device information given the initial path which is a symlink. Note: I saw that the tomoyo module has something like that but I was looking for the generic implementation of the kernel if one exists. Thanks David

4 6

Re: spinlock variable protection
by Matwey V. Kornilov Jan. 30, 2015

Jan. 30, 2015

Nice, thank you 30.01.2015 18:24 пользователь "Malte Vesper" < malte.vesper(a)postgrad.manchester.ac.uk> написал: > Spinlocks imply memory barriers as far as I am aware... > > Read here: http://lxr.free-electrons.com/source/Documentation/memory- > barriers.txt#L1634 > > On 30/01/15 14:20, Matwey V. Kornilov wrote: > >> 2015-01-30 16:52 GMT+03:00 buyitian <buyitian(a)gmail.com>: >> >>> Please check the assembly code to double confirm the GCC behavior. >>> Why will GCC change the order as what you mentioned? Only assembly code >>> can tell you. >>> >> It does not change at the moment. I think it can change it. >> >> Because from line >> ret = hdl->count; >> until line >> return ret; >> there is no access to either ret or hdl->count. So it is reasonable to >> optimizer to think that their values are the same and eliminate >> unneeded variable. >> >> >

1 0

Intercepting memory mapped files
by Kunal Baweja Jan. 30, 2015

Jan. 30, 2015

Hi, I am currently working on implementing a simple encrypted file system using a stackable file system WrapFS <http://wrapfs.filesystems.org/>. In order to do so, as I read in the WrapFS mailing list <http://www.fsl.cs.sunysb.edu/pipermail/wrapfs/2011-November/000058.html> one needs to implement address space operations, which I have done and posted on my github at this link <https://github.com/bawejakunal/wrapfs-addresspace-operations/blob/master/mm…> and it works fine. But now when I am trying to modify the data before being written in wrapfs_lower() function I get a blank output in files written out. Please guide where am I going wrong in modifying the data to be written and what could be the best way to decrypt it ? Thanks *Kunal Baweja* Undergraduate B.E. (Hons.) Computer Science Birla Institute Of Technology & Science, Pilani K.K. Birla Goa Campus +91 9049655665

4 10

x86 boot gdt
by Alexander Kuleshov Jan. 30, 2015

Jan. 30, 2015

Hello all, Have a little question about gdt initialization. We can see the following: [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff), in the arch/x86/boot/pm.c. Why accessed bit is set here (9b)? I see that it was not set (9a) in the earliest versions. What's reason was to change it? -- _________________________ 0xAX

1 0

Kernel source tagging
by Xavier Naveira Jan. 30, 2015

Jan. 30, 2015

Hi all, Why doesn't the Linus tree have tags for the minor version updates of the kernel, ie, 3.18.1, 3.18.2 etc? If i do: $ git tag | grep 3\.18 The result is: v3.18 v3.18-rc1 v3.18-rc2 v3.18-rc3 v3.18-rc4 v3.18-rc5 v3.18-rc6 v3.18-rc7 X

2 2

RE: Kernel 2.6.32.60 64bit Crash/Hung
by Giridhara RP (grp) Jan. 30, 2015

Jan. 30, 2015

All, I Changed CONFIG_NR_CPUS=64 to CONFIG_NR_CPUS=128 and kernel did not panic. Please note my setup has 4CPUs , each has 10 cores and supports Hyper threading. So, linux creates 4 x 10 x 2 logical CPUs. Thanks Giri

1 0

Can I submit simple patches like this to the primary ML?
by Vinícius Tinti Jan. 29, 2015

Jan. 29, 2015

This is a simple patch that initializes a function with NULL to avoid some compiler warnings. In such cases should I proceed as a normal patch or it is better to send to another ML like to one for trivial patches? Thanks, Tinti

3 6

Eudyptula Challenge Task 03 Queue Question
by Patrick Creech Jan. 29, 2015

Jan. 29, 2015

Hi! Just have a minor question on task 03's queue. I submitted my solution on 1-18-2015, and the queue status in the response was: .. number 23 in line, and the response that is next is from "14 Jan 2015 15:07:46 +0530" ... I resubmitted it yesterday due to no response, and the queue status was: ... number 53 in line, and the response that is next is from "14 Jan 2015 19:29:35 +0100" ... Just curious if this was normal or not. Thanks, Patrick

3 3