January 2015 - kernelnewbies@kernelnewbies.org

Difference between INIT_LIST_HEAD and LIST_HEAD_INIT
by nawab Jan. 6, 2015

Jan. 6, 2015

hi friends , i have a simple doubt when i was looking on linux/list.h I have seen that INIT_LIST_HEAD and LIST_HEAD_INIT are performing the same functionality,the major difference is the argument passed. When we have to use INIT_LIST_HEAD and LIST_HEAD_INIT??

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Wait times for patch submission
by Mandeep Sandhu Jan. 6, 2015

Jan. 6, 2015

Hi All, I wanted to check with ppl who frequently post patches to LKML on how long should one should wait before resending the patches in case there's no response to them. I had sent a patch on Greg KH's staging-next tree, on 16 Dec '14 to LKML and the relevant maintainers. I got a mail from Greg's friendly bot stating that the branch was closed and that the patches will be looked at once the merge window closes. Do I need to resend the patches again or will they be picked up from the maintainer's queue? Thanks, -mandeep

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Why the Email of @yahoo.com can't subscribe majordomo@vger.kernel.org ?
by lx Jan. 6, 2015

Jan. 6, 2015

hi all: I want to subscribe the majordomo(a)vger.kernel.org about netdev. But It don't work. The error message is: ######################## Sorry, we were unable to deliver your message to the following address. <majordomo(a)vger.kernel.org> <majordomo(a)vger.kernel.org>: Remote host said: 553 5.7.1 Hello [106.10.151.226], for your MAIL FROM address <lxgeek(a)yahoo.com> <lxgeek(a)yahoo.com> policy analysis reported: Your address is not liked source for email [MAIL_FROM] --- Below this line is a copy of the message. Received: from [106.10.166.120] by nm33.bullet.mail.sg3.yahoo.com with NNFMP; 29 Dec 2014 05:50:14 -0000 Received: from [106.10.167.174] by tm9.bullet.mail.sg3.yahoo.com with NNFMP; 29 Dec 2014 05:50:14 -0000 Received: from [127.0.0.1] by smtp147.mail.sg3.yahoo.com with NNFMP; 29 Dec 2014 05:50:14 -0000 X-Yahoo-Newman-Id: 541845.56363.bm(a)smtp147.mail.sg3.yahoo.com X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: 3s0rdfQVM1lPcl7PYi8obCNwfrPXi49mnORqxY8zxPBP3GZ WJNE8J4eollOsC50XIZRciC4O4E_2ak65nfZUWIcWZ5l3LThPaGj2NLnRRfb ae0Zm7lhLNH5GsT8BCLBOB4KuUeLqo7XFm1uOKu3noMmqMF5qFY9AFTLJRQ4 GBGBn2RLuVQD2SNVV8kbd0otyfm.jJK.AIyCnUymqqi45ux3R1Vatzzu4rhk N5BsL2uYUufhcjbKBl8vSClY4dcBN6gvwCT21AVlPYza0ekIPAS7Y2XPdAKK vJnRPbj8hTidiNVr__g8eTjWBLR7sMPrRZV351BsXsyUrfw4sQitpvobSko0 K_Jg9o_aFPuMgr5qCAS1DjKUVd2JcpGU5.XVp58mZXwi0rg1uePB4oRavhv_ Uj1zX4WBx8q7FSfWsbMGZvSZZpYLWuBrEKNHO34BXJqDr1HzW_ObaY.nzzxC SpuijN8aIG380ZIhgW7xcd6sYG2fFIb6Gxyfg0A6JFhvasNVdXbdcDvJGw_D zsYWQ706pxDyoznM1hIXt5B9NwImQu7NLtUPSxA-- X-Yahoo-SMTP: Ot9DgBiswBD6.gcTBOjHB_vvEA-- Message-ID: <54A0EB96.3060500(a)yahoo.com> <54A0EB96.3060500(a)yahoo.com> Date: Mon, 29 Dec 2014 13:50:14 +0800 From: lx <lxgeek(a)yahoo.com> <lxgeek(a)yahoo.com> User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: majordomo(a)vger.kernel.org Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit subscribe netdev ######################## How to fix it? Thank you.

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Boot up fail with linux-next source code tag next-20141226
by Sunil Shahu Jan. 6, 2015

Jan. 6, 2015

Hi, I am trying to build and boot linux-next kernel tree. My original kernel with Ubuntu 12.04 LTS was 3.5.0-23-generic. I checked out code with tag next-20141226. I generated a ".config" file with "make localmodconfig". I installed modules and kernel.On restart PC do not boot up. I then checked out tag v3.16-rc3 and booted. It worked pretty good and booted properly. I had few question from this exercise: 1) Why my PC didn't boot up with linux-next kernel?2) Do I need to apply any specific patches to boot mainline linux-next kernel on my Ubuntu 12.04 PC?3) How do people test mainline kernel-next? Do they apply their OS specific patch on linux-next tree or test linux-next on some specific OS? Thanks,Sunil.

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Question on checpatch.pl warning -- possible unnecessary 'out of memory' message.
by Bas Peters Jan. 5, 2015

Jan. 5, 2015

Dear all, I'm fixing up my first driver (drivers/isdn/gigaset) to get some experience submitting patches. When I run checkpatch.pl on some of the code, I get the following warning: ./drivers/isdn/gigaset/capi.c:337: WARNING: Possible unnecessary 'out of memory' message The corresponding code is: cskb = alloc_skb(CAPI_DATA_B3_CONF_LEN, GFP_ATOMIC); if (!cskb) { dev_err(cs->dev, "%s: out of memory\n", __func__); return; } All instances of this warning refer to usage of alloc_skb using the GFP_ATOMIC flag. Why does checkpatch show this warning? Is it not good practice to _always_ check whether allocation succeeded or not? I hope someone can explain the nature of this warning and, if right, what it should look like. With kind regards, Bas Peters

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Re: Understanding of write file operation in char driver
by me storage Jan. 3, 2015

Jan. 3, 2015

Hi All, Thanks Victor Can any one please tell me difference between kernal space & user space in code perspective i.e in write function const char *buffer should point to address of *hello* in RAM so how it is changing when i am accessing through some kernel function because it is also accessing the same RAM address? Thanks & Regards Prasad On 1 January 2015 at 21:20, Victor Rodriguez <vm.rod25(a)gmail.com> wrote: > On Thu, Jan 1, 2015 at 2:24 AM, me storage <me.storage126(a)gmail.com> > wrote: > > I am learning char drivers.But i didn't understand write operation of > char > > device driver properly. the below is my write operation > > > > static ssize_t dev_write(struct file *fil,const char __user *buff,size_t > > len,loff_t *off) > > { > > pr_info("user input string %s\n",buff); > > pr_info("user input string len %d\n",len); > > return len; > > } > > > > my doubt is if i write into my device like > > echo "hello" > /dev/myDev > > > > it is giving different behaviour like below is the dmesg > > [20596.975355] user input string hello > > [20596.975355] 77b9e4 > > [20596.975355] insmod insmod > > [20596.975355] n/zeitgeist-daemon > > [20596.975355] atives > > [20596.975355] > > [20596.975355] vars "${upargs[@]}" > > [20596.975355] cur cword words=(); > > [20596.975355] local upargs=() upvars=() vcur vcword vprev vwords; > > [20596.975355] while getopts "c:i:n:p:w:" flag "$@"; do > > [20596.975355] case $flag in > > [20596.975355] c) > > [20596.975355] vcur=$OPTARG > > [20596.975355] ;; > > [20596.975355] i) > > [20596.975355] vcword=$OPTARG > > [20596.975355] ;; > > [20596.975355] n) > > [20596.975355] exclude=$OPTARG > > [20596.975355] ;; > > [20596.975355] p) > > [20596.975355] vprev=$OPTARG > > [20596.975355] ;; > > [20596.975355] w) > > [20596.975355] vwords=$OPTARG > > [20596.975355] ;; > > [20596.975358] user input string len 6 > > [20596.975361] Device closed > > > > so i didn't understand what is happening inside .Can any one please > explain > > what is happening? > > HI Prasad > > The problem is ont he part where you try to print the buffer on dmesg. > I tested this code ( the base full code is on my github repo as > char_simple.c *): > > 106 static ssize_t device_write(struct file *filp, > 107 const char *buf, > 108 size_t len, > 109 loff_t * off) > 110 { > 111 > 112 procfs_buffer_size = len; > 113 > 114 > 115 if ( copy_from_user(buffer_data, buf, procfs_buffer_size) > ) { > 116 return -EFAULT; > 117 } > 118 *off += len; > 119 > 120 pr_info("user input string %s\n",buffer_data); > 121 //pr_info("user input string len > %lu\n",procfs_buffer_size); > 122 > 123 return procfs_buffer_size; > 124 } > > And the dmesg output is : > > [ 2735.251589] Hello from the Kernel !!! (how cool is that) > [ 2735.251600] Major Number = 244 > [ 2735.251604] Name = mychardriver > [ 2735.251607] Generate the device file with mknod > /dev/mychardriver c 244 0 > [ 2766.806455] user input string hello there > > Remember to first do the copy from user space and then print that > variable instead of just the buff variable. Print the len is fine > (https://gist.github.com/17twenty/6313566 ) however when you try to > print the string from the user space , there is where we have the > problems (I did the experiment ) > > Here are some useful links: > > http://www.ibm.com/developerworks/library/l-kernel-memory-access/ > https://www.kernel.org/doc/htmldocs/kernel-api/ch04s02.html > > Hope it helps > > Regards > > Victor Rodriguez > > *char_simple.c : > > https://github.com/VictorRodriguez/linux_device_drivers_tutorial/blob/maste… > > > > > > > > > > Thanks & Regards > > Prasad > > > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > >

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Doubt In Char Drivers
by me storage Jan. 3, 2015

Jan. 3, 2015

Hi All, I am following LDD3 for Char Drivers. So we writing a kernel module(char driver) after that creating a char file which is representation of Character Device. So my doubt is how we will communicate with real hardware device let suppose how to communicate with our monitor . Can any one please explain how we will communicate with real hardware for read/write calls? And what is mknod is doing internally when we are creating char/block devices? Thanks in Advance

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Understanding of write file operation in char driver
by me storage Jan. 1, 2015

Jan. 1, 2015

I am learning char drivers.But i didn't understand write operation of char device driver properly. the below is my write operation static ssize_t dev_write(struct file *fil,const char __user *buff,size_t len,loff_t *off) { pr_info("user input string %s\n",buff); pr_info("user input string len %d\n",len); return len; } my doubt is if i write into my device like echo "hello" > /dev/myDev it is giving different behaviour like below is the dmesg [20596.975355] user input string hello [20596.975355] 77b9e4 [20596.975355] insmod insmod [20596.975355] n/zeitgeist-daemon [20596.975355] atives [20596.975355] [20596.975355] vars "${upargs[@]}" [20596.975355] cur cword words=(); [20596.975355] local upargs=() upvars=() vcur vcword vprev vwords; [20596.975355] while getopts "c:i:n:p:w:" flag "$@"; do [20596.975355] case $flag in [20596.975355] c) [20596.975355] vcur=$OPTARG [20596.975355] ;; [20596.975355] i) [20596.975355] vcword=$OPTARG [20596.975355] ;; [20596.975355] n) [20596.975355] exclude=$OPTARG [20596.975355] ;; [20596.975355] p) [20596.975355] vprev=$OPTARG [20596.975355] ;; [20596.975355] w) [20596.975355] vwords=$OPTARG [20596.975355] ;; [20596.975358] user input string len 6 [20596.975361] Device closed so i didn't understand what is happening inside .Can any one please explain what is happening? Thanks & Regards Prasad

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