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

some questions about log level
by loody June 29, 2012

June 29, 2012

hi all: my questions are below: 1. Can I temporarily let kernel message show in stdout? I google some key word as "console_loglevel" and I found following methods: a. echo 8 > /proc/sys/kernel/printk b. write a simple program which calling "klogctl(8, NULL, level)" Then I purposely connect/disconnect USB, but my console keep quiet. But dmesg shows connect/disconnect messages. 2. what is differences between above a and b methods? Are they not to used to change console_loglevel? 3. is it possible the max level of "console_loglevel" doesn't mean it will show on stdout? -- Thanks for your help

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identity mapped paging
by Vaibhav Jain June 19, 2012

June 19, 2012

I am not clear about the use of identity mapped paging while paging is being enabled by the operating system. Also I don't understand at what point are the identity mappings no longer useful.According to this article http://geezer.osdevbrasil.net/osd/mem/index.htm#identity - "The page table entries used to identity-map kernel memory can be deleted once paging and virtual addresses are enabled." Can somebody please explain? Thanks Vaibhav Jain

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Question about tlv message support
by NorthPole May 18, 2012

May 18, 2012

Hello everyone I'm completely new to linux kernel and I would be grateful if you could help me get started. I read some basic things about the kernel. But I couldnt find anything relevant to the question below. So: Does the kernel have any support for the construction and encoding of type/length/value (TLV) or other information element messages? if it has(or if you dont know) where can I find a list or more documentation?

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tty driver
by Sri Ram Vemulpali April 30, 2012

April 30, 2012

Hello All, I am working on paging feature on tty, pty outputting. Is there anyway I can do paging output at tty drivers by way of setting some options using ioctl or .... Please let me know, to give you some idea if you type ls -l | more on command prompt you see the output in paging fashion. This is the kind of feature I want it on tty fds. Please let me know if anyone has any better idea. thanks. -- Regards, Sri.

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how to get create/compile time of vmlinux
by 卜弋天 April 30, 2012

April 30, 2012

Hi All: i have a vmlinux file, how can i know when it is created/compiled? thanks. Best Regards

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Found duplicate entries in kernel IPV6 routing table
by Nitin Yadav April 27, 2012

April 27, 2012

kernel version : Linux- 3.1 Module : IPV6 Description of problem: Found duplicate default route (::/0) entries in kernel IPV6 routing table . route -6 -n Kernel IPv6 routing table Destination Next Hop Flag Met Ref Use If fe80::/64 :: U 256 0 0 eth1 fe80::/64 :: U 256 0 0 eth2 fe80::/64 :: U 256 0 0 eth3 fe80::/64 :: U 256 0 0 eth0 ::/0 :: !n -1 1 1 lo ::1/128 :: Un 0 1 12 lo fe80::7ae7:d1ff:fe94:915a/128 :: Un 0 1 0 lo fe80::7ae7:d1ff:fe94:915c/128 :: Un 0 1 0 lo fe80::7ae7:d1ff:fe94:915e/128 :: Un 0 1 0 lo fe80::7ae7:d1ff:fe94:9160/128 :: Un 0 1 0 lo ff00::/8 :: U 256 0 0 eth1 ff00::/8 :: U 256 0 0 eth2 ff00::/8 :: U 256 0 0 eth3 ff00::/8 :: U 256 0 0 eth0 ::/0 :: !n -1 1 1 lo Please let me know about this situation , why there is duplicate entries are present in kernel IPV6 routing table. Thanks ! Nitin Yadav Information transmitted by this e-mail is proprietary to MphasiS, its associated companies and/ or its customers and is intended for use only by the individual or entity to which it is addressed, and may contain information that is privileged, confidential or exempt from disclosure under applicable law. If you are not the intended recipient or it appears that this mail has been forwarded to you without proper authority, you are notified that any use or dissemination of this information in any manner is strictly prohibited. In such cases, please notify us immediately at mailmaster(a)mphasis.com and delete this mail from your records.

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CFS mechanism...
by Anirban Roy April 27, 2012

April 27, 2012

Hi, i have one basic doubt in the CFS algorithm. Following is my doubts. I am using 2.6.23 as the kernel version In CFS , when a Sleeping task wants to get inside the Running Queue ( cfs_rq ) , Then it calcluates the its own "vruntime" depend on "cfs_rq->min_vruntime" and "sysctl_sched_latency". In function "place_entity" , "vruntime" is assigned the value. in brief ===> se.vruntime = cfs_rq->min_vruntime - sysctl_sched_latency ( equation 1 ) So the process which wants to get inserted in CFS QUEUE , will have a KEY ==> "se->vruntime - cfs_rq->min_vruntime" ( equation 2 ) If we take merge equation 1 and equation 2 .. then KEY is equal to "-sysctl_sched_latency". So when the Process will be added to RB TREE , then this new Task will always be the leftmost entry, as its KEY is in negative value. I thought if we add the value of "sysctl_sched_latency" in equation "1" , then it would have been right as the New task will be waiting minimum "sysctl_sched_latency" nano seconds before getting schedule ( if run queue is heavily loaded ). Can somebody help me in understanding why we are Subtracting "sysctl_sched_latency" instead of Adding Help will be greatly appreciated. below i have added the code for "place_entity" and "entity_key" regards Anirban Roy static void place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) { u64 vruntime; vruntime = cfs_rq->min_vruntime; if (sched_feat(USE_TREE_AVG)) { struct sched_entity *last = __pick_last_entity(cfs_rq); if (last) { vruntime += last->vruntime; vruntime >>= 1; } } else if (sched_feat(APPROX_AVG) && cfs_rq->nr_running) vruntime += __sched_vslice(cfs_rq->nr_running)/2; if (initial && sched_feat(START_DEBIT)) vruntime += __sched_vslice(cfs_rq->nr_running + 1); if (!initial) { if (sched_feat(NEW_FAIR_SLEEPERS)) vruntime -= sysctl_sched_latency; vruntime = max_t(s64, vruntime, se->vruntime); } se->vruntime = vruntime; } static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se) { return se->vruntime - cfs_rq->min_vruntime; }

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stdout to console
by Arun KS April 27, 2012

April 27, 2012

Hello Guys, We all know that when an application writes to stdout, data ends up in the console. Okey so if I m on my development board and if I run an app, all the prints comes to the console (eg /dev/ttyS0). If I m on any server using ssh and all apps prints comes on my putty (eg through /dev/pts/176). Where is the code which maps fd 1 to the console in kernel? If you guys have any pointers, please share. While opening a device (for eg /dev/something), the vfs calls that drivers, whose major and minor number matches. But in case of stdout, how vfs resolves the write to the fd 1 and send it to the corresponding console driver? Thanks, Arun

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Re: Kernelnewbies Digest, Vol 17, Issue 44
by Jeshwanth Kumar N K Jeshu April 27, 2012

April 27, 2012

Hello guys, I am writing a user space code for pwm controller in beaglebone, but the drivers are in the form of files, so when I am writing the code I got a doubt that, if we keep access the files it may take more processor time so any other way is there to access or this is the best way ? On Thu, Apr 26, 2012 at 9:30 PM, <kernelnewbies-request(a)kernelnewbies.org>wrote: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: Profiling my Modules (Daniel Baluta) > 2. Re: Linux Driver Project (Bj?rn Mork) > 3. Re: Profiling my Modules (Rishi Agrawal) > 4. Re: Linux Driver Project (Bj?rn Mork) > 5. freelance kernel work (Christopher Harvey) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 26 Apr 2012 15:42:57 +0300 > From: Daniel Baluta <daniel.baluta(a)gmail.com> > Subject: Re: Profiling my Modules > To: Rishi Agrawal <rishi.b.agrawal(a)gmail.com> > Cc: kernelnewbies(a)kernelnewbies.org > Message-ID: > <CAEnQRZCf1zjMAQSe8uuYTr7px6-K51fLpB%2BvwY3SMkDXimcpxw(a)mail.gmail.com > > > Content-Type: text/plain; charset=ISO-8859-1 > > On Thu, Apr 26, 2012 at 10:33 AM, Rishi Agrawal > <rishi.b.agrawal(a)gmail.com> wrote: > > Hi All, > > > > I have a kernel module which has functions which take a lot of time in > > execution. I am curious to know how can I profile it, and find out the > > functions taking most of the time. > > > > I saw Oprofile, but it seems that I will have to build the whole kernel, > and > > also that it will be difficult to profile my module through it. > > > > Any trick or tool will do. > > Hello, > > Have a look at perf [1]. > > thanks, > Daniel. > > [1] https://perf.wiki.kernel.org/ > > > > ------------------------------ > > Message: 2 > Date: Thu, 26 Apr 2012 15:16:59 +0200 > From: Bj?rn Mork <bjorn(a)mork.no> > Subject: Re: Linux Driver Project > To: Rabee Al-Maqabi <rabee.almaqabi(a)gmail.com> > Cc: Javier Martinez Canillas <martinez.javier(a)gmail.com>, > kernelnewbies(a)kernelnewbies.org > Message-ID: <87fwbqeipg.fsf(a)nemi.mork.no> > Content-Type: text/plain; charset=utf-8 > > Rabee Al-Maqabi <rabee.almaqabi(a)gmail.com> writes: > > > Thank you for your reply. Linux Device Drivers is indeed a great book. I > > have read it in addition to Understanding the Linux Kernel and I have > > experimented with my Linux box. At this point, I would like to have a > > real-world experience and write a driver for a piece of hardware not yet > > supported. > > How about a fingerprint scanner? If you've got a modern laptop then > chances are good that you already own such a device. And it's > most likely unsupported. Some might say that's because it's useless :-) > > Otherwise I'd recommend looking through your box of unused devices. No > need to go out and buy anything if all you want is to write some > driver. > > Or see > http://www.linuxdriverproject.org/foswiki/bin/view/Main/DriversNeeded > if you are open to buying some new device for this project. > > You won't find any datasheets or any other documentation, though... > Manufacturers smart enough to provide documentation usually get drivers > written for their devices in no time. But some still hold it to > themselves. Go figure. > > > Bj?rn > > > > ------------------------------ > > Message: 3 > Date: Thu, 26 Apr 2012 19:01:00 +0530 > From: Rishi Agrawal <rishi.b.agrawal(a)gmail.com> > Subject: Re: Profiling my Modules > To: Daniel Baluta <daniel.baluta(a)gmail.com> > Cc: kernelnewbies(a)kernelnewbies.org > Message-ID: > <CADDndfPtRis6CuXJN7D0v%3DsnCJ8b_hS0eW2cQoBekXE3UtyXSw(a)mail.gmail.com > > > Content-Type: text/plain; charset="iso-8859-1" > > Thanks a lot, I will have a look at it and see if it helps. > > On Thu, Apr 26, 2012 at 6:12 PM, Daniel Baluta <daniel.baluta(a)gmail.com > >wrote: > > > On Thu, Apr 26, 2012 at 10:33 AM, Rishi Agrawal > > <rishi.b.agrawal(a)gmail.com> wrote: > > > Hi All, > > > > > > I have a kernel module which has functions which take a lot of time in > > > execution. I am curious to know how can I profile it, and find out the > > > functions taking most of the time. > > > > > > I saw Oprofile, but it seems that I will have to build the whole > kernel, > > and > > > also that it will be difficult to profile my module through it. > > > > > > Any trick or tool will do. > > > > Hello, > > > > Have a look at perf [1]. > > > > thanks, > > Daniel. > > > > [1] https://perf.wiki.kernel.org/ > > > > > > -- > Regards, > Rishi Agrawal >

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Reg: 16 unknown bytes in ESp packet(IPSEC)
by Mukesh Yadav April 26, 2012

April 26, 2012

Hi, Not able to understand 16 byetes in ESP packet present after sequence no and before Original IP header while doing tunnel mode Ipsec with ESP. Details are as below. I am trying to achieve Ipsec functionality using fast-path application which will do encryption/decryption using some hardware(Cavium) specific API. This application will by-pass the IP layer of kernel.. Keys for start-up are pre-shared. Communication is done between two machine A and B. On Machine A running i386 linux, SA/SP database are updated using setkey utility and packets is encrypted/decrypted using kernel Ipsec. On Machine B Cavium h/w, keys are pre-shared to application performing Ipsec functionlity... Example: M/c A configuration: add 50.50.50.51 50.50.50.53 esp 15701 -E aes-cbc "0123456789abcdef"; spdadd 10.10.10.20 10.10.10.21 any -P out ipsec esp/tunnel/50.50.50.51 50.50.50.53/require I am able to decrypt received packets on machine B send by M/c A and send encrypted packet to M/c A. Issue: 1. Not able to find what are 16 bytes present after sequence no in ESP header and before original IP header representing... Decrypted Packet on machine B is like below Ethernet header 14 bytes Outer Ip header 20 bytes ESP header SPI 4 bytes Seq no 4 bytes Some data 16 bytes ??????? Original IP header 20 bytes UDP header Payload data Padding Pad lenght Next Ip header 2. Packets send from machine B are encrypted and received as ESP packet on machine A.. Not sure if decryption is happening fine...Seems packets are dropped at IP layer.. Is there way to confirm if packet are decrypted fine by kernel IPSEC... Encrypted packet send by Machine B is having encrypted payload(of original IP header plus data) after Sequence number of ESP header... Seems 16 bytes mentioned above play role for successful decryption at machine A running Linux IPSEC Any Inputs for same will be appreciated for same Cheers Mukesh

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