June 2012 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Makefile to compile kernel modules
by Amit Nagal June 28, 2012

June 28, 2012

Hi , i want to compile a standalone kernel module for linux kernel version 2.6 or 3.0 . A basic Makefile goes like this : ================== obj-m += hello-1.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 want to add debugging symbols information ( using -g option ) also via CFLAGS usage flag . can i be guided how to modify this basic Makefile to add CFLAGS information for adding debugging symbols information . Regards Amit Nagal

2 1

Re: zcache and zsmalloc
by Asim June 27, 2012

June 27, 2012

Yeah - I see lots of BUG_ON(!irqs_disabled()) in zcache code while placing and compressing the page(and also other places). I am not clear what you mean when you say zcache does so for other reasons. My guess was when clean zcache_put_page is called it holds locks (mapping->tree_lock) that conflicts xsmalloc pool allocations. If zsmalloc has no such issues, can these be removed? Thanks, Asim - Adding the correct kernel newbies address with entire conversation intact for reference. On Wed, Jun 27, 2012 at 1:26 PM, Seth Jennings <sjenning(a)linux.vnet.ibm.com> wrote: > On 06/27/2012 01:04 PM, Asim wrote: >> This query relates zcache and the new zsmalloc patches. >> >> I was looking through zcache code and your various zsmalloc patches. I >> am aware the zcache disables interrupts due to xvmalloc pool >> allocations.However, does the zsmalloc code also needs to disable >> interrupts while placing a page in zcache? > > (Adding Nitin to Cc) > > None of the functions need interrupts/preemption to be > disabled before calling them, even though zcache does for > other reasons. > > zs_map_object() will return with page faults and preemption > disabled by kmap_atomic() and get_cpu_var() respectively. > This is to insure atomic access to the mapping_area > structure. They are re-enabled in zs_unmap_object(). > > -- > Seth >

1 0

Re: How to start with USB device driver.
by Jeshwanth Kumar N K Jeshu June 27, 2012

June 27, 2012

Hello Pravin It is working fine for me, goto http://www.linuxforu.com/ In search bar : linux device drivers series. And if you want USB device driver : goto http://www.linuxforu.com/2011/10/usb-drivers-in-linux-1/ And while replying put cc to kernelnewbies(a)kernelnewbies.org On 6/27/12, Pravin Shedage <pravinshedage2008(a)gmail.com> wrote: > http://www.linuxforu.com/tag/linux-device-drivers-series/ > > this link not working can you please help me ? > > On Mon, Jun 25, 2012 at 12:31 PM, jeshwanth Kumar N K < > jeshkumar555(a)gmail.com> wrote: > >> Hello Srinidhi >> >> Thanks for the reference :). Ya PIC development board means, I have a >> development board of a microcontroller (PIC18F4550) from microchip , it >> has usb module so I am planning to use that as the device by program it >> to >> communicate with my Linux ( I am new to that also, have to learn ). So if >> any device you suggest ? Which s available in Bangalore ? >> >> Sent from my HTC >> >> >> ----- Reply message ----- >> From: "Srinidhi M" <srinidhi.m26(a)gmail.com> >> Date: Mon, Jun 25, 2012 10:25 am >> Subject: How to start with USB device driver. >> To: "jeshwanth Kumar N K" <jeshkumar555(a)gmail.com> >> Cc: <kernelnewbies(a)kernelnewbies.org> >> >> >> On Sun, Jun 24, 2012 at 10:12 AM, jeshwanth Kumar N K >> <jeshkumar555(a)gmail.com> wrote: >> > Hello all >> > >> > I have basic knowledge of character device driver, I would like to >> > learn >> > writing a simple character driver for USB because on my laptop only I >> > can >> > communicate with usb I don't have any Boards. Can anyone suggest some >> > tutorials or simple project to learn USB device driver ? And suggest me >> any >> > hardware for other side also. Now I am planning to use my PIC board (it >> has >> > usb) to communicate with linux. >> > >> >> Hi Jeshwanth, >> >> You can go through the following link. >> http://lwn.net/images/pdf/LDD3/ch13.pdf >> >> I think, you need a device for testing your written source code. Could >> you please tell me details about your PIC board as I do not understand >> it clearly? >> >> Regards, >> Srinidhi. >> >> >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >> > > > -- > Thanks & Regards,* > ---------PraviN---------* > -- Regards Jeshwanth Kumar N K +91-7411483498

1 0

neigh_tbl_lock usage in net/core/neighbour.c
by Meng Zhang June 27, 2012

June 27, 2012

Hi~ @list I'm on my way to jump into the kernel network stack;) And I find the usage of neigh_tbl_lock might not make sense in following functions static int neigh_delete(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg) static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg) They both have the following code snippets read_lock(&neigh_tbl_lock); --L1 for (tbl = neigh_tables; tbl; tbl = tbl->next) { --L2 struct neighbour *neigh; --L3 if (tbl->family != ndm->ndm_family) --L4 continue; --L5 read_unlock(&neigh_tbl_lock); --L6 if (nla_len(dst_attr) < tbl->key_len) --L7 goto out_dev_put; IMHO, there might be some race condition after L6. I mean when the L7 use the tbl, is it possible other processor releasing the table entry? Am I wrong? -- Yours sincerely Jammy

1 0

Missing Key-codes from input.h file.
by Dharam Kumar June 27, 2012

June 27, 2012

Hi, I'm working on a module which is an input device and hence it needs to report certain key events. While browsing through the <linux/input.h>, I did find most of the key-codes(which I need to use)already defined but not all. Few of the KEY_xxx which i could not find are: a.) A Key for going to the previous channel. b.) Keys for Moving upper-right, lower-right, upper-left and lower-left direction(probably a GUI(grid of icons),where you move diagonally) d.) A key for Subpicture (this 'subpicture' key is defined in CEA-931C). Does anybody have any idea about this? - Dharam

3 9

what does smp_cross_call does?
by Jacky lin June 27, 2012

June 27, 2012

Hi all, Could any one tell me what does smp_cross_call() means? My device (Dual call) encounter a soft lockup here with following info: [ 101.654724:0] PC is at generic_exec_single+0x7c/0x94 [ 101.659698:0] LR is at arch_send_call_function_single_ipi+0x3c/0x48 I check the code, and find the LR is point to smp_cross_call() void arch_send_call_function_single_ipi(int cpu) { smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE); } Cheers, Jacky

2 1

vmalloc size
by Subramaniam Appadodharana June 27, 2012

June 27, 2012

Hi All, I am trying to understand how vmalloc memory is reserved in kernel. In 3.4+ latest kernel, the default vmalloc size is 240MB. Is this a carveout from the 1GiB memory that kernel has? In other words can I do a __pa(VMALLOC_START) or __pa(VMALLOC_END) or __pa(highmemory) irrespective of the vmalloc size that I request, say doing vmalloc=1G? Thank you and Regards Subbu

4 11

Writing a new device driver
by Malice June 26, 2012

June 26, 2012

Hi I'm planning to write a new device driver on linux kernel . The device i intend to write will be a device that'll pipe the data coming into it to another computer that'll be also having the same device . So in short the device'll be readable/writable and should communicate through network . I know it sounds like a socket but the idea would be to implement a interface in shell so that if you type | root@host$echo "Hi">>mydevice | will transfer the word hi to the system on the other side of network (and may be configure it to store on file). This is a leisure time project i intend to do and it sounds much like sockets and other already existing implementations . Well the questions regarding the design for device implementations are : 1)Should i use a block or a character device . The advantage i see for a block device is that if i am a initiating a complete file transfer through the device(which i in tend to support later) , then it would be fast . 2)How do i write the data on the network . I'm familiar with sockets and stuff , but using sockets from with in the kernel has performance issues(I read it somewhere, after all sockets was desined to be used in userspace) . Will using netfilter or other stuffs work ?Maybe crafting the packet directly would help :-)? Any innovations are welcome 3)How do i configure the driver , like how do i let it know that it should connect to a specific host >in user space programs we usually do this by config files , but to change the connection settings of a driver how do you manage it ? (sysfs ?? Frankly i never worked with sysfs or proc/ ) 4)Now as the design specifies all the transfer of files is in kernel space . When i transfer huge chunks of data through kernel space , will it slow down the system ?. The design shouldnt overload the system , doing it in a pre-empitble kernel will help, but are there other charecterstics i should be aware of to make the design as efficient as possible (i'm doing it on the latest linux kernel) ? 5)And i dont want to leave a huge memory imprint so is there any way i can reduce it while tranferring of data , may be cacheing data on disk ? 6)I will have to design a user space programme to co ordinate the driver wont i ? I cannot let the driver alone do the whole task , tat wud be tedious Comments Welcome I've also posted the same question at stackoverflow too http://stackoverflow.com/questions/11167424/writing-a-new-device-driver Regards Malice

2 1

geting weird semi-random panic on kmalloc
by NorthPole June 26, 2012

June 26, 2012

Hello everyone I'm making my first steps in the linux kernel developpement by trying to add some functionality in a kernel module I have a problem that I cant seem to grasp and would greatly appreciate any help. I have this piece of code: http://pastebin.com/igP7255S which is called by this: for(i=0;i<250;i++) registerTvlv(i,0x01,1,&batadv_ogm_packet->gw_flags,bat_priv,batadv_ogm_packet); This is supposed to add 250 distinct tlvs in the list batadv_ogm_packet->gw_flags is used both above and bellow the invocation and the module doesnt crash the same stands for these two bat_priv and batadv_ogm_packet when I run the kernel code on an open-wrt build for x86 which is run virtualized under a standard qemu running on debian squeeze produces this output http://pastebin.com/tY3Vkzvw (in short it prints everything as its supposed to do for a random number of iterations between 3 and 24 and the the kernel oops happens) But i cant understand why the problem seems to happen at the kmalloc line (havent figured how to use gdb for open wrt kernel debugging yet so i'm relying on printk for debugging) the qemu instance loads with these setings screen qemu\ -no-acpi -m 128M \ -net vde,sock=num1.ctl,port=1 -net nic,macaddr=fe:fe:00:00:01:01 \ -net nic -net tap,ifname=tapwrt1,script=no,downscript=no \ -nographic \ num1.image Thank you for your time and answers Spyros

3 7

How to start with USB device driver.
by jeshwanth Kumar N K June 25, 2012

June 25, 2012

Hello all I have basic knowledge of character device driver, I would like to learn writing a simple character driver for USB because on my laptop only I can communicate with usb I don't have any Boards. Can anyone suggest some tutorials or simple project to learn USB device driver ? And suggest me any hardware for other side also. Now I am planning to use my PIC board (it has usb) to communicate with linux. Thanks in advance. Sent from my HTC

3 2