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Compile the driver against kernel source requires a build kernel ??
by Sraddha Aug. 24, 2011

Aug. 24, 2011

I am trying to build a led driver for the samsung kernel 2.6.35.7 I have 2.6.35-22-generic installed on my host machine Now I thought is I could take the header files for the 2.6.35.7 kernel from the net sudo apt-get install kernel-headers-2.6.35.7: Error:Unable to locate package kernel-headers-2.6.35.7 Any suggestion for the header files can I use the header files of 2.6.35 like if I type sudo apt-get install kernel-headers-2.6.35 and use these header files for the led driver compilation I have the samsung kernel source , so Maybe I just compile the led driver against this source without compiling the entire samsung kernel . Plz iluminate . Regards Sraddha

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Question on __pv_stub
by subin gangadharan Aug. 24, 2011

Aug. 24, 2011

Hi All, I am just trying to understand __va macro. I can see two definitions,one in include/asm-generic/page.h and other is in arch/arm/include/asm/memory.h. The first definition is just adding PAGE_OFFSET,but the second one boil downs to __pv_stub.Could anybody please help me to understand what this __pv_stub for? With Regards Subin Gangadharan Everything should be made as simple as possible,but not simpler.

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What does drop_caches do?
by Prateek Sharma Aug. 24, 2011

Aug. 24, 2011

Hello everyone, I've been trying to understand the role of the pagecache, starting with drop_caches and observing what it does. From my understanding of the code (fs/drop_caches.c) , it walks over all the open files/inodes, and invalidates all the mapped pages. Pages which are *not* dropped are either dirty,in-use,anonymous,mapped(to pagetable),or writeback) . Is my understanding correct? But, when i run drop_caches, there are still some pages which show up as cached. Why arent all cache pages getting dropped ? My confusion runs much deeper. What exactly constitutes the pagecache? All filebacked pages ? mmaped files ? If i copy a bunch of files, why does my cache get polluted with those pages? Thanks for reading. I'd be grateful if someone can enlighten me about some pagecache internals . (Please keep me CC'ed) <begin experiment> root@tripitz:/etc/apt# free -m total used free shared buffers cached Mem: 1995 1854 140 0 79 700 -/+ buffers/cache: 1074 920 Swap: 4767 762 4005 root@tripitz:/etc/apt# echo 3 > /proc/sys/vm/drop_caches root@tripitz:/etc/apt# free -m total used free shared buffers cached Mem: 1995 1373 621 0 0 363 -/+ buffers/cache: 1009 985 Swap: 4767 762 4005 <end experiment>

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startingKernelProgramming
by Srinidhi Rao Aug. 24, 2011

Aug. 24, 2011

Hi all, I am in the initial hard steps of learning the nuances of kernel programming, as to begin what are all the modules (header files) to use its data-structures be included to go about, as I tried this source: src: http://tldp.org/LDP/lkmpg/2.6/html/x121.html /* * hello-1.c - The simplest kernel module. */ #include <linux/module.h> /* Needed by all modules */ #include <linux/kernel.h> /* Needed for KERN_INFO */ int init_module(void) { printk(KERN_INFO "Hello world 1.\n"); /* * A non 0 return means init_module failed; module can't be loaded. */ return 0; } void cleanup_module(void) { printk(KERN_INFO "Goodbye\n"); } as compilation followed this: box@x86:~$ cc kernel_hello.c kernel_hello.c:3: fatal error: linux/module.h: No such file or directory compilation terminated. -- Thanks and Regards, Srinidhi. ---- All our knowledge has its origins in our perception. -- Leonardo da Vinci. ---- Tell me and I forget. Teach me and I remember. Involve me and I learn. -- Benjamin Franklin.

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where is the definition of irq_desc array?
by LovelyLich Aug. 24, 2011

Aug. 24, 2011

Hi all, First, I have to say sorry for my pool English , because I am not a native English speaker. I know this is too simple, but I have tried hours to get the definition (not declaration) of irq_desc array in the interrupt subsys. Actually, I have been troubled in finding the definition. Because the array name( irq_desc) is same as the name of struct irq_desc. I think the irq_desc array is the core of interrupt subsys, so I didn't describe it in details. I tried describing my question , if there is something not clear, please let me know ,and I will try .. Sorry for my pool English again....

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question about staging tree branches
by Prashant Shah Aug. 23, 2011

Aug. 23, 2011

Hi, There are 4 branches in the staging tree remotes/staging/master remotes/staging/ralink remotes/staging/staging-linus remotes/staging/staging-next Is the staging-linus is what Linus merges and staging-next is merged by linux-next tree ? What is ra-link for ? Regards.

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Re: TCP - RST flag
by Daniel Baluta Aug. 23, 2011

Aug. 23, 2011

On Wed, Aug 24, 2011 at 12:50 AM, Eric Dumazet <eric.dumazet(a)gmail.com> wrote: > Le mercredi 24 août 2011 à 00:32 +0300, Daniel Baluta a écrit : >> On Tue, Aug 23, 2011 at 11:55 PM, Eric Dumazet <eric.dumazet(a)gmail.com> wrote: > >> > TCP in RFC 1122 section 4.2.2.13: >> > >> > "A host MAY implement a "half-duplex" TCP close sequence, so that an >> > application that has called CLOSE cannot continue to read data from the >> > connection. If such a host issues a CLOSE call while received data is >> > still pending in TCP, or if new data is received after CLOSE is called, >> > its TCP SHOULD send a RST to show that data was lost." >> >> So, this means that server's CLOSE operation is issued while received >> data is still pending? I will analyze ftp's server code, but this is strange >> since P4 [221 Have a nice day!\r\n] it is generated as a response for >> P3 [QUIT\r\n]. So P4 must have been fully received. >> > > tcpdump only shows TCP stack did receive the frame, not that it was > _read_ by application. > > Only strace could eventually say if the input queue was really drained > before the close(). > Maybe server decided to close the connexion before reading the QUIT > command from client. > >> Also, looking at the capture no data is received from the client after >> server calls CLOSE (P5) (there are only ACKs and FIN - P6, P7, P8). > > That doesnt matter. > > If data was received (and ACKnowledged by TCP stack) _before_ close(fd), > but not yet read by application, TCP must send an RST to be RFC > compliant. I see. Thanks a lot for your explanations. I will further use strace to see what's going on. Daniel.

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Re: TCP - RST flag
by Daniel Baluta Aug. 23, 2011

Aug. 23, 2011

On Tue, Aug 23, 2011 at 11:55 PM, Eric Dumazet <eric.dumazet(a)gmail.com> wrote: > Le mardi 23 août 2011 à 23:31 +0300, Daniel Baluta a écrit : >> Hello, >> >> Please help me understanding the behavior of the following >> TCP conversation. >> >> You can find bellow a snippet of the (FTP) conversation captured both >> on client (C) and server (S). >> >> [client]$ tcpdump -n -r client-6-conv.cap >> [P1] 49.045690 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq >> 197:220, ack 81, win 757, length 23 >> [P2] 49.046600 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, >> win 738, length 0 >> [P3] 49.047462 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [P.], seq >> 81:87, ack 220, win 738, length 6 >> [P5] 49.048757 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [F.], seq >> 242, ack 87, win 757, length 0 >> [P6] 49.048794 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, >> win 738, options [nop,nop,sack 1 {242:243}], length 0 >> [P4] 49.048801 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq >> 220:242, ack 87, win 757, length 22 >> [P7] 49.048833 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 243, >> win 715, length 0 >> [P8] 49.049566 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [F.], seq 87, >> ack 243, win 715, length 0 >> [P9] 49.050889 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [R], seq >> 1672731590, win 0, length 0 >> >> [server]$ tcpdump -n -r server-6-conv.cap >> [P1] 49.059740 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq >> 197:220, ack 81, win 757, length 23 >> [P2] 49.061394 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, >> win 738, length 0 >> [P3] 49.061760 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [P.], seq >> 81:87, ack 220, win 738, length 6 >> [P4] 49.062794 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq >> 220:242, ack 87, win 757, length 22 >> [P5] 49.062843 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [F.], seq >> 242, ack 87, win 757, length 0 >> [P6] 49.063808 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, >> win 738, options [nop,nop,sack 1 {242:243}], length 0 >> [P7] 49.063823 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 243, >> win 715, length 0 >> [P8] 49.064271 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [F.], seq 87, >> ack 243, win 715, length 0 >> [P9] 49.064481 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [R], seq >> 1672731590, win 0, length 0 >> >> What happens is that servers sends packets P4 and P5, but client >> receives P5 before P4. >> Since SACK is enabled, client will send a SACK (P6) ack-ing P5. >> >> Then client sees P4, and will send an ack (P7) for P4, then sends P8 >> with FIN flag set. >> What I don't understand, is why server responds with RST (P9) instead of ACK? >> >> This is was obtained on 2.6.32.43. I have also attached full capture files. >> >> I am reading TCP's RFC and kernel code, but so far I haven't reached >> a conclusion. > > TCP in RFC 1122 section 4.2.2.13: > > "A host MAY implement a "half-duplex" TCP close sequence, so that an > application that has called CLOSE cannot continue to read data from the > connection. If such a host issues a CLOSE call while received data is > still pending in TCP, or if new data is received after CLOSE is called, > its TCP SHOULD send a RST to show that data was lost." So, this means that server's CLOSE operation is issued while received data is still pending? I will analyze ftp's server code, but this is strange since P4 [221 Have a nice day!\r\n] it is generated as a response for P3 [QUIT\r\n]. So P4 must have been fully received. Also, looking at the capture no data is received from the client after server calls CLOSE (P5) (there are only ACKs and FIN - P6, P7, P8). > This is why some apps first call shutdown(), then drain receive queue, > then close() This makes sense :). thanks Eric. Daniel.

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TCP - RST flag
by Daniel Baluta Aug. 23, 2011

Aug. 23, 2011

Hello, Please help me understanding the behavior of the following TCP conversation. You can find bellow a snippet of the (FTP) conversation captured both on client (C) and server (S). [client]$ tcpdump -n -r client-6-conv.cap [P1] 49.045690 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq 197:220, ack 81, win 757, length 23 [P2] 49.046600 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, win 738, length 0 [P3] 49.047462 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [P.], seq 81:87, ack 220, win 738, length 6 [P5] 49.048757 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [F.], seq 242, ack 87, win 757, length 0 [P6] 49.048794 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, win 738, options [nop,nop,sack 1 {242:243}], length 0 [P4] 49.048801 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq 220:242, ack 87, win 757, length 22 [P7] 49.048833 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 243, win 715, length 0 [P8] 49.049566 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [F.], seq 87, ack 243, win 715, length 0 [P9] 49.050889 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [R], seq 1672731590, win 0, length 0 [server]$ tcpdump -n -r server-6-conv.cap [P1] 49.059740 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq 197:220, ack 81, win 757, length 23 [P2] 49.061394 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, win 738, length 0 [P3] 49.061760 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [P.], seq 81:87, ack 220, win 738, length 6 [P4] 49.062794 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [P.], seq 220:242, ack 87, win 757, length 22 [P5] 49.062843 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [F.], seq 242, ack 87, win 757, length 0 [P6] 49.063808 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 220, win 738, options [nop,nop,sack 1 {242:243}], length 0 [P7] 49.063823 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [.], ack 243, win 715, length 0 [P8] 49.064271 IP 10.10.0.20.58277 > 10.10.0.1.21: Flags [F.], seq 87, ack 243, win 715, length 0 [P9] 49.064481 IP 10.10.0.1.21 > 10.10.0.20.58277: Flags [R], seq 1672731590, win 0, length 0 What happens is that servers sends packets P4 and P5, but client receives P5 before P4. Since SACK is enabled, client will send a SACK (P6) ack-ing P5. Then client sees P4, and will send an ack (P7) for P4, then sends P8 with FIN flag set. What I don't understand, is why server responds with RST (P9) instead of ACK? This is was obtained on 2.6.32.43. I have also attached full capture files. I am reading TCP's RFC and kernel code, but so far I haven't reached a conclusion. thanks, Daniel.

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Difference between logical and physical cpu hotplug
by Vaibhav Jain Aug. 23, 2011

Aug. 23, 2011

Hi, I need to know the difference between making a cpu logically offline and physically offline. I have read that the following command $ echo 0 > /sys/device/system/cpu/<cpu number>/online makes a cpu logically offline. It frees the cpu from interrupts and migrates running processes. But then what does it mean to make a cpu physically offline ? I referred to following article : http://www.kernel.org/doc/Documentation/cpu-hotplug.txt Here is the relevant excerpt : Q: Does hot-add/hot-remove refer to physical add/remove of cpus? A: The usage of hot-add/remove may not be very consistently used in the code. CONFIG_HOTPLUG_CPU enables logical online/offline capability in the kernel. To support physical addition/removal, one would need some BIOS hooks and the platform should have something like an attention button in PCI hotplug. CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of CPUs. Please help! Thanks Vaibhav Jain

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