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How to view processor schedule history
by J.Hwan Kim Nov. 6, 2013

Nov. 6, 2013

Hi, everyone Can I find the schedule history of CPU in system, for example /proc Thanks in advance J.Hwan Kim

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Writing to user file from kernel
by neha naik Nov. 6, 2013

Nov. 6, 2013

Hi, I know this is taboo and so on.But, i would like to know the difference between 'vfs_read' (similar to description in linux journal article : http://www.linuxjournal.com/article/8110) and the call 'splice_direct_to_actor'. 'vfs_read' is strightforward but i don't understand the api 'splice_direct_to_actor'. Is there any documentation which will explain it to me and where it is used. Because as i see it you can read a file using either of the two 'vfs_read' or 'splice_direct_to_actor'. But, which is better. Regards, Neha

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Block device driver question
by neha naik Nov. 5, 2013

Nov. 5, 2013

Hi, I am writing a block device driver and i am using the 'blq_queue_make_request' call while registering my block device driver. Now as far as i understand this will bypass the linux kernel queue for each block device driver (bypassing the elevator algorithm etc). However, i am still not very clear about exactly how i get a request. 1. Consider i am doing a dd on the block device directly : Will it bypass the buffer cache(/page cache) or will it use it. Example if i register my block device with set_blocksize() as 512. And i do a dd of 512 bytes will i get a read because it passes through the buffer cache and since the minimum page size is 4096 it has to read the page first and then pass it to me. I am still unclear about the 'page' in the bvec. What does that refer to? Is it a page from the page cache or a user buffer (DMA). 2. Another thing i am not clear about is a queue. When i register my driver, the 'make_request' function gets called whenever there is an io. Now in my device driver, i have some more logic about writing this io i.e some time may be spent in the device driver for each io. In such a case, if i get two ios on the same block one after the other (say one is writing 'a' and the other is writing 'b') then isn't it possible that i may end up passing 'b' followed by 'a' to the layer below me (changing the order because thread 'a' took more time than thread 'b'). Then in that case should i be using a queue in my layer - put the ios in the queue whenever i get a call to 'make_request'. Another thread keeps pulling the ios from the queue and processing them and passing it to the layer below. Regards, Neha

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How can I send multiple patches?
by Aldo Iljazi Nov. 5, 2013

Nov. 5, 2013

Hello everyone, I have a question. Let's say I have four patches, how can I send them? Should I send them one-by-one or can I send them all together? Could you give me one example? Thanks. -- Aldo Iljazi

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own distribution Centos 6.4
by PV Juliet Nov. 5, 2013

Nov. 5, 2013

Hi, I am trying to make a distribution for Centos 6.4 . I was gone the steps from this link ( http://smorgasbork.com/component/content/article/35-linux/128-building-a-cu…) . After installing with minimal distribution machine is gives this error . Kernel Panic - not syncing: Attempted to kill init! Pid: 1 comm: init Not tainted. I have put all the dependencies also . Why this problem comes? can u tell me isit any other way to make the distribution for CentOs 6.4?? Thanks and Reagrds Juliet

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Festival Shutdown : Kernelnewbies Digest, Vol 36, Issue 8
by hemal.patel＠slscorp.com Nov. 5, 2013

Nov. 5, 2013

Hi, Due to Diwali Festival, SLS will be closed from Oct. 31th to Nov. 6th. We will return on Nov. 7th to the office. For urgent matter please call on 001-408-852-0067. For more information about Diwali: http://en.wikipedia.org/wiki/Diwali Regards, Hemal Patel

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Address Types in Linux
by Anup Buchke Nov. 5, 2013

Nov. 5, 2013

Hi all, I am studying LDD3. It mentions the following types of address which is creating some confusion. User Virtual Address : The address space of a process. This ranges from 0-3Gb for 32-bit machines. Kernel Logical Address : This is the range of address for which there exist no virtual mapping. They add some offset into the logical address and get the corresponding physical address. This is also referred as "Low memory." Kmalloc gives this type of address. Kernel virtual address : This is the range of address for which virtual mapping exist. Kernel has to go through the paging mechanism to get the physical address and then access the location. This is referred as "High Memory". Vmalloc gives this type of address. If this goes through paging mechanism...Can there be Page Fault for this type of access?...What kinds of kernel code/data are placed in "High Memory". Both Kernel (virtual and logical) address ranges in 3-4GB for 32bit machines. Please let me know if this understanding is proper. Also any good comments to enhance my understanding will be helpful and appreciated. Thanks Anup

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RE: Fwd: Packet Loss (Robert Clove)
by Murali Annamneni Nov. 5, 2013

Nov. 5, 2013

Hi Robert, You can write your own kernel (using netfilter framework) module to count the number of packets received at kernel. And, with this kernel module you can have the flexibility of filtering the packets you are sending from packeth. Thanks & Regards Murali ------------------------------- Date: Sat, 2 Nov 2013 07:28:24 -0700 From: Robert Clove <cloverobert(a)gmail.com> Subject: Fwd: Packet Loss To: kernelnewbies <kernelnewbies(a)kernelnewbies.org> Message-ID: <CAEMktPXwKMEEuds9syAV4Y7DzHPQQnVoiaHMC2L%3DEVTJ6Up0VA(a)mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" On Mon, Oct 28, 2013 at 5:44 PM, Kristof Provost <kristof(a)sigsegv.be> wrote: > On 2013-10-28 17:32:43 (+0530), Robert Clove <cloverobert(a)gmail.com> > wrote: > > Kind of Packets :- *UDP* > > How are you generating them? :-* Packeth ( > > http://packeth.sourceforge.net/packeth/Home.html)* > > kernel version : uname -r - *2.6.32-358.18.1.el6.x86_64 > > * > > Are you *SURE* you're sending 1000? - *ya checked through packeth > > status bar and also through ifconfig command* I have connected them > > through LAN cable (cat 6) back to back. > > > > Changed cable but no use. > > What should i do? > > > Break down the problem. Get that smart switch to tell you if the > packets are lost by the sender of the receiver. > > Test if it's bidirectional (i.e. does it still happen if the switch > the sender and receiver)? > > Does it still happen if you send only 100 packets? Do you still lose > 30% then, or do you lose more or less? > > Perhaps try a kernel that isn't nearly five years old too. > > Also, don't top-post. > > Regards, > Kristof > > Hey Sir, I just want to know are there any driver or kernel parameters that we can adjust to get the better packet capture? Thanks

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Re: IPv4 Fragmentation in a IPIP6 tunnel
by Pietro Paolini Nov. 4, 2013

Nov. 4, 2013

Hello, I investigated better the problem, the MTU (WAN and LAN side) is 1500 bytes, I am running a test which send a packet of 1496 bytes LAN side and is not fragmented. The problem appears because the size of the IPv6 header plus the payload (1496 bytes) is greater then the MTU (1500), at that point the IPv4 packet is fragmented while my expectation is that just the IPv6 should be. I placed a printk in the ip_fragment function and I can see that the packet is fragmented over there, my expectation is that piece of code should not been ever executed since i am sending over IPv6, I would remark that I don't have a fully understanding of the linux kernel networking stack implementation. Where should the IPv6 fragmentation be done ? Pietro Paolini pulsarpietro(a)aol.com -----Original Message----- From: Fan Du <fan.du(a)windriver.com> To: Pietro Paolini <pulsarpietro(a)aol.com> Cc: kernelnewbies <kernelnewbies(a)kernelnewbies.org>; p.paolini <p.paolini(a)genexis.eu> Sent: Thu, Oct 31, 2013 10:39 am Subject: Re: IPv4 Fragmentation in a IPIP6 tunnel Hi Pietro On 2013年10月30日 23:02, Pietro Paolini wrote: > Hello everyone, > I am working for an embedded Linux firmware running on a CPE and I am > using an IP4 over IPv6 tunnel configured as following: > > ip -f inet6 tunnel add tun1 mode ipip6 remote XX:XX:XX local XX:XX:XX > dev eth0 > > And it works fine until I don't try to test the fragment case: I send a > too big UDP packet and my expectation - and requirement (sob) - would > be a IPv6 packet fragmentation but what I get is a double > fragmentation (IPv4 and IPv6), then, summarizing: > > IPv4 --> [IPv4-1-segment][IPv6] [IPv4-2-segment][IPv6] I didn't manage to test this, but a first glance make me think your expectation has one requirement: UDP packet + IPv4 header doesn't not exceed mtu of IPv4 src->dst, *AND* UDP packet + IPv4 header exceed the IPv6 tunnel mtu. UDP packet first has to fit into IPv4 layer size(phase 1), and then tunneled in IPv6 style(phase 2). So two kinds of mtu involved here. > Looking at the kernel code - which in I am not an expert - I observed > that the function ip_finish_output : > > #if defined(CONFIG_NETFILTER)&& defined(CONFIG_XFRM) > /* Policy lookup after SNAT yielded a new policy */ > if (skb_dst(skb)->xfrm != NULL) { > IPCB(skb)->flags |= IPSKB_REROUTED; > return dst_output(skb); > } > #endif > #if defined(CONFIG_INET_IPSEC_OFFLOAD) > if ((skb->ipsec_offload == 0)&& > skb->len> ip_skb_dst_mtu(skb)&& !skb_is_gso(skb)) > #else > if (skb->len> ip_skb_dst_mtu(skb)&& !skb_is_gso(skb)) > #endif > return ip_fragment(skb, ip_finish_output2); > else > return ip_finish_output2(skb); > > Does not care about it, it just fragments if the MTU does not match. > > Is there any options to disable the fragmentation on IPV4 ? I am > misconfiguring something ? Why does the ipip6 has this wrong behavior ? > > Thanks in advance, > Pietro. > > Pietro Paolini > pulsarpietro(a)aol.com > > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > -- 浮沉随浪只记今朝笑 --fan

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One confusion about PTE modification on page migration
by frank kang Nov. 4, 2013

Nov. 4, 2013

Hello all, I have one confusion about PTE modification on page migration. Can anyone help me clarify it? As we know, if process access the virtual addresss with null PTE entry, it will result in page fault. In page fault routine, it will check PTE entry to determine whether it is swap case, (handle_pte_fault) if (pte_none(entry)) { .... return do_anonymous_page(...); } return do_swap_page(...); But, in try_to_unmap_one_anon(...), the pte entry is cleared before it has new swap entry. pteval = ptep_clear_flush_notify(vma, address, pte); ... set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); I feel confused about the above atomic operation. That is, If the pte is zeroed and new swap entry is not set yet. Some process accesses to the address and page fault is raised. In the above routine from page fault, pte_none() will return TRUE and it will go to do_anonymous_page(...), instead of do_swap_page(...). Am i right? I don't know if it is my fault or not. Can someone help me? Thanks! Frank

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