January 2015 - kernelnewbies@kernelnewbies.org

SIze of a file shows 124 GB while available size is less than 16 GB
by manty kuma Jan. 21, 2015

Jan. 21, 2015

Hi All, I am working with bionic c(Android). There is a file that I generated which is showing 124 GB(ls -l) size. Whereas the actual available memory on the partition is less than 16 GB. I am trying to debug but unable to reach any conclusion. What could be the possible reason? Has someone seen like this before? Posting it here as I think it has got something to do with linux internals. I am guessing fseek's offset somewhere has gone wrong. But any directions would be very helpful. Regards, Manty

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Maintainer Hasn't Picked up my patch after git resend for Ipmi subsystem
by nick Jan. 20, 2015

Jan. 20, 2015

Greetings All, I am unable to get through to the maintainer of the ipmi subsystem for a patch,that I am resending. Does anyone known if they are really busy with other kernel work? Cheers Nick

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Debugging an ARP issue (no resp to ARP requests)
by Mandeep Sandhu Jan. 20, 2015

Jan. 20, 2015

Hi All, Please let me know if this is not the correct ML for such a question (or if there's a more appropriate list for it). I'm currently debugging an issue where Linux is not responding to ARP requests (testing with custom network interface h/w). I have 2 network interfaces which are basically interfaces on a custom network device sitting on the PCI bus. My setup looks like follows: xeth0 - 192.168.2.1 xeth2 - 192.168.2.2 xeth0/2 are the interfaces created for the custom device (via a lkm) Both these interfaces are on the local machine and are connected back-to-back on the custom device, so packets sent from one arrive on the other. I'm testing this setup by sending a single ARP pack, forced out of one interface, for the other interface's IP. $ sudo arping -c 1 -i xeth0 192.168.2.2 ARPING 192.168.2.2 --- 192.168.2.2 statistics --- 1 packets transmitted, 0 packets received, 100% unanswered (0 extra) If I start tcpdump on the receive interface (xeth2), I see the ARP packet arrive, but I don't see any response go out (I've attached the pcap file for anyone interested in looking at the received packet). The ARP packet's contents seem to be proper under wireshark. Is there any statistics I can look at to see if the packet was dropped by linux during ARP processing? I've put debug stmts in the LKM, but I don't see the kernel IP layer calling the xmit function for an ARP reply (however the xmit function for the ARP request, from xeth0, is being called). I don't see any drops in "netstat -s" output as well. Any hints appreciated. Thanks, -mandeep

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Address_space_operations write_begin vs prepare_write ?
by Kunal Baweja Jan. 19, 2015

Jan. 19, 2015

Hi, I am new to kernel coding and right now trying to implement address space operations on top of WrapFS. I noticed that the address_space_operations declaration has a field write_begin where I was expecting prepare_write. Is it just a change of name with newer versions of kernel or is there some significant change that has been made to it ? Thanks *Kunal Baweja* Undergraduate B.E. (Hons.) Computer Science Birla Institute Of Technology & Science, Pilani K.K. Birla Goa Campus +91 9049655665

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container_of
by Simon Brand Jan. 19, 2015

Jan. 19, 2015

Good evening, i read the article about the container_of function: http://www.kroah.com/log/linux/container_of.html I understand what it does and how it works. I thought, it could be simplified by replacing it through this: #define container_of(ptr, type, member) ({ \ (type *)( (char *)ptr - offsetof(type,member) );}) Original: #define container_of(ptr, type, member) ({ \ const typeof( ((type *)0)->member ) *__mptr = (ptr); (type *)( (char *)__mptr - offsetof(type,member) );}) ptr has the type of a pointer to the member, which should be the same as __mptr? The value should although be the same. First I tried it in a self written script, then replaced it in include/linux/kernel.h and compiled it as usermode linux -> working well. Then I compiled it and run it in a VM, but it is not working. Can you please explain to me, why the original version is always working and "mine" is not? Thank you for your time! Regards, Simon

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How to use git-send-email for deep threading
by Sunil Shahu Jan. 19, 2015

Jan. 19, 2015

Hello, I am working on eudyptula challenge and I have to send solution file and later patches on that file using git-send-email. I have to send email in such a way that it looks something like this in receiver's email inbox. Two Solution Files (Makefile and .c driver file) └─> [PATCH 01/02] Patch 1 on earlier solution file └─> [PATCH 02/02] Patch 2 on earlier solution file I tired using different options in git send-email, but what I get is incorrect linking of mails. Two Solution Files (Makefile and .c driver file) [PATCH 01/02] Patch 1 on earlier solution file └─> [PATCH 02/02] Patch 2 on earlier solution file I am not able to send two files using git send-email for the first email. I have to use --force to send any source file. Even in this, only first file is attached in mail. I also tried send first file using web browser mail client and then sending patches using git send-email, but it also do not work as expected. I have read git-send-email documentation but not able to comprehend how I can achieve my requirement from it. Can someone please give pointers on how I can send email correctly as per my requirement using git-send-email?

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Make cscope fails for me now as of lastest commits on Linus's tree
by nick Jan. 19, 2015

Jan. 19, 2015

Greetings Kernel Developers, After pulling the latest kernel commits for Linus’s tree, I am getting a build failure with make cscope. Below is the error messages. find: unknown predicate `--cc' I am unsure of why I am getting this and if this is a bug or an issue with my machine. Nick

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Fwd: Question about kernel interfaces
by Siddhartha De Jan. 18, 2015

Jan. 18, 2015

FYI ... ---------- Forwarded message ---------- From: One Thousand Gnomes <gnomes(a)lxorguk.ukuu.org.uk> Date: Wed, Jan 14, 2015 at 10:03 PM Subject: Re: Question about kernel interfaces To: Siddhartha De <siddhartha.de87(a)gmail.com> Cc: linux-kernel <linux-kernel(a)vger.kernel.org> > Just wanted to point out something :- > > Quoting from makelinux website :- > http://www.makelinux.net/books/lkd2/ch17lev1sec8 > > "The sysfs filesystem is currently the place for implementing > functionality previously reserved for ioctl() calls on device nodes or > the procfs filesystem. These days, the chic thing to do is implement > such functionality as sysfs attributes in the appropriate directory. > For example, instead of a new ioctl() on a device node, add a sysfs > attribute in the driver's sysfs directory. Such an approach avoids the > type-unsafe use of obscure ioctl() arguments and the haphazard mess of > /proc. " And is wrong. Certainly rather clueless people had the idea they could make ioctl go away using sysfs, and then everyone wrote about it. Anyone who actually thought about the problem realised immediately they are not semantically equivalent. > sysfs is the new ioctl And as was pointed out even then they are not semantically equivalent so everyone who was talking about "sysfs being the new ioctl" was basically talking out the wrong end. What was done was to stop filling drivers with ioctls for pieces of general information which didn't have a context attached to it or sequence. Things like power state, what type it is, what bus it is on etc. That avoided having zillions of ioctls but at the cost of memory. > Taking this idea further , could we also expose driver IOCTL's over > the network ? > > For eg to open the cd rom drive we would be calling the following url :- You could but why would you make the network visible. If you look at real clustered systems they all hide the network. You don't care where it is, often you don't even care where the drive is. eject /dev/cdrom on such a system lets the kernel figure out who to ask to eject it. The job of an OS is to abstract details like that. In a clustered OS I want to be able to type mount mydisk and I don't care who, where or how it gets mounted so long as it appears. Alan

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kernel source code cross reference search
by Code Grep Jan. 18, 2015

Jan. 18, 2015

Hi guys, Just to share with you another linux cross reference search here: https://code-grep.com/view/project/54b083273b2082684a000008/linux-3.19-rc2 Feel free to feedback to me for any improvements.

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Contributing via kernel-janitors
by Dr. George E. Moore Jan. 16, 2015

Jan. 16, 2015

I'm unclear as to how via kernel-janitors, I can support patches to the kernel. Are bug/documentation anomalies already identified in some archive, or are we expected to choose a subsystem, search for such anomalies as described in the KernelJanitor/Todo page, acknowledge our willingness to make fixes and submit patches to kernel-janitors@vgerkernel.org? What kernel subsystems are current being reviewed and patched by kernel-janitors? I'm certainly willing to lend my support to this work; hwever, I could use some guidance.

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