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download 2.6.11 ver.
by esmaeil mirzaee Sept. 26, 2011

Sept. 26, 2011

Hi apologize for weak English. I'm reading the Understand Linux Kernel 3rd edition, according to that book for accomplishment understand I need 2.6.11 version of linux. How can I download it? As you know the kernel.org is under maintain. -- Best Esmaeil https://sites.google.com/site/esmaeilmirzaee

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Debugging IP packet through Linux stack
by Abu Rasheda Sept. 24, 2011

Sept. 24, 2011

I am inserting packets into Linux stack and they are accepted by net_rx function, but are latter dropped. What tools are available in Linux kernel to for debugging this issue.

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What's wrong on this mmap() ?
by Andrea Gasparini Sept. 23, 2011

Sept. 23, 2011

Hi, I'm having some problem understanding how mmap really works. I have a (dummy) driver that allocate some memory (4k), and gives it to a userspace through mmap() - the usual remap_pfn_pages found in every example. The userspace can read the memory correctly, but can't write to it. (though it maps with PROT_WRITE) As the manpage says: PROT_WRITE - Pages may be written. I'm attaching both the driver and the userspace testbed, with the hope someone tells me what's wrong with this. Note that I tested on ARM and x86 architectures, and different kernel, so It seems more likely a fault of mine, that a kernel strangeness. (obviusly, you'll say... :P ) The userspace log are something like that: Base userspace address for mmapped buffer is 0xb7786000 Wrote 00 in user-space 0xb7786000. Reading from it seems 00 Wrote 01 in user-space 0xb7786001. Reading from it seems 01 Wrote 02 in user-space 0xb7786002. Reading from it seems 02 [ .... snip ... ] While the kernel are: allocated: 4096 @virt: c7000000 @phys: 8c800000 virtToPhys(): 87000000 mmap worked. vmaflasg: 40184477 phys: 87000000 virt: c7000000 VMA open: vma->vm_start: 40236000 - vma->pgoffs: 87000 - vma->vm_end: 40237000, vma_flags: 40184477 VMA close: vma->vm_start: 40236000 - vma->pgoffs: 87000 - vma->vm_end: 40237000, vma_flags: 40184477 00 ff fe fd fc fb fa f9 f8 f7 f6 f5 f4 f3 f2 f1 f0 ef ee ed ec eb ea e9 e8 e7 e6 e5 e4 e3 e2 e1 Regards, bye! -- - Andrea Gasparini - ----------------------------------------------- -------- https://launchpad.net/~gaspa --------- ----- HomePage: http://gaspa.yattaweb.it ------

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How to traverse or walk, the kernel's page table without mem_map?
by Jeff Donner Sept. 23, 2011

Sept. 23, 2011

Hi; I have a 4 CPU machine, x86_64, with 8GB of ram, and am using the 3.0 kernel. I'm taking a kernel class and one of my assignments is to print the address of mem_map and its number of entries and then, translate that address to physical and, walk the whole kernel page table counting some flags (just to do it). My problem is, that I cannot see mem_map from my exercise module, and it's because my kernel is .config'd to NEED_MULTIPLE_NODES, and in mm/memory.c: #ifndef CONFIG_NEED_MULTIPLE_NODES /* use the per-pgdat data instead for discontigmem - mbligh */ unsigned long max_mapnr; struct page *mem_map; EXPORT_SYMBOL(max_mapnr); EXPORT_SYMBOL(mem_map); #endif So, with my configuration the kernel isn't letting me see a mem_map. Now in mm/Kconfig, NEED_MULTIPLE_NODES seems to depend on DISCONTIGMEM config NEED_MULTIPLE_NODES def_bool y depends on DISCONTIGMEM || NUMA Which may not have anything to do with anything, but I'm leery of changing such a deep setting. I'd like to, if possible, a) find out the right way to traverse the global kernel page table (ie to complete the task as stated), adapted to how my kernel is now -- or -- b) I have the idea that the lack of mem_map is due to DISCONTIGMEM, which may be due to its being an x86_64 machine (my guess). I'd like to find out what I need to do to simplify my kernel so that I can just walk along mem_map as originally instructed. I appreciate any ideas; Thanks, Jeff

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Optimizing the performance of the Scheduler in the Kernel 3.0
by Edward Alvarez Sept. 23, 2011

Sept. 23, 2011

Greetings, <kernelnewbies(a)kernelnewbies.org> I want to optimize the performance of the scheduler in the Kernel 3.0 in order to increase the number of calls a Sip proxy server can handle. I read about the scheduler in the Kernel 2.6 and was able to find the variables MIN_TIMESLICE, MAX_TIMESLICE, PRIO_BONUS_RATIO, MAX_SLEEP_AVG and STARVATION_LIMIT. If I tune this variables I can tweak the performance of the scheduler, but in the new kernel I cant find any documentation that allows to successfully modify the scheduler. I would gladly appreciate any information related to the scheduler in the new kernel, or documentation about the new variables that are similar to the ones I mentioned. Thanks in advance for your time. Edward Alvarez.

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(no subject)
by 毕春雷 Sept. 23, 2011

Sept. 23, 2011

nirvanacn2011(a)hotmail.com

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what does sys_sync() function do when suspend is called?
by sandeep kumar Sept. 22, 2011

Sept. 22, 2011

Hi all, "sys_sync()" function is used in enter_suspend(). It is taking a long time, when data transfer is happening, thus taking more time for the deivce to suspend. I am basically does not know much about filesystems, still wondering what sys_sync() function does? When suspend is called before suspending the devices we will call sys_sync() function. All that i know is it "syncs the filesystems..!!!" I tried to see the function implementation but it is a system call. My questions are.. 1) where its implementation will be present(system calls like those)? 2) briefly what it does? 3) why it is taking more time when data transfer is happening? -- With regards, Sandeep Kumar Anantapalli,

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question on memory mapping one page at a time
by Sri Ram Vemulpali Sept. 22, 2011

Sept. 22, 2011

Hi all, can anyone please explain the following code, what it is doing. I want the first few statements of the code, as they are calculating page frame number. This is little confusing, thanks in advance. struct page *simple_vma_nopage(struct vm_area_struct *vma, unsigned long address, int *type) { struct page *pageptr; unsigned long offset = vma->vm_pgoff << PAGE_SHIFT; unsigned long physaddr = address - vma->vm_start + offset; unsigned long pageframe = physaddr >> PAGE_SHIFT; if (!pfn_valid(pageframe)) return NOPAGE_SIGBUS; pageptr = pfn_to_page(pageframe); get_page(pageptr); if (type) *type = VM_FAULT_MINOR; return pageptr; } -- Regards, Sri.

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TCP_DELACK_MIN vs TCP_ATO_MIN
by Daniel Baluta Sept. 22, 2011

Sept. 22, 2011

Hello, RFC2582, Section 4.2 says: "... an ACK SHOULD be generated for at least every second full-sized segment, and MUST be generated within 500 ms of the arrival of the first unacknowledged packet. ". I guess that the delayed ACK timeout is computed in tcp_send_delayed_ack: === void tcp_send_delayed_ack(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); int ato = icsk->icsk_ack.ato; unsigned long timeout; /* .... */ /* Stay within the limit we were given */ timeout = jiffies + ato; ==== Can one explain what is the difference between TCP_DELACK_MIN and TCP_ATO_MIN, specifically if the timeout (ato) is always in the interval [TCP_DELACK_MIN, TCP_DELACK_MAX] ? I want to make the delayed ack timeout configurable as some guys tried here [1], so for this reason I plan to make TCP_DELACK_MIN and TCP_DELACK_MAX tunable via proc entries. thanks, Daniel. [1] http://kerneltrap.org/mailarchive/linux-netdev/2008/9/9/3245554

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Cannot read using USB Skeleton Driver
by Felix Varghese Sept. 21, 2011

Sept. 21, 2011

Hi, I have been trying to communicate with a custom usb device from a SAM9G20-EK board using the usb-skeleton.c driver example in the linux source. I modified the driver to add my device's vendor and product id. The USB device enumerates with two bulk endpoints - one IN and one OUT. The (modified) skel driver successfully detects my device and I get a minor number allocated. After creating a device file with that minor number, I am able to write into the device by typing 'echo "HI" > /dev/mydevice'. I verified that this data arrives at my device intact. Next, I started sending data back from the device and tried to read it back using 'cat /dev/mydevice'. The problem is that read not only doesn't work, but also makes the app get totally stuck. Ctrl-C doesn't work and I have to reboot the board. Some debugging using printk's led me to the following snippet which seems to be causing the hang. If I change the wait to a wait_for_completion_interruptible, Ctrl-C starts working, but still no data is received. if (!dev->processed_urb) { /* * the URB hasn't been processed * do it now */ wait_for_completion(&dev->bulk_in_completion); dev->bulk_in_copied = 0; dev->processed_urb = 1; } Oh, btw I am using linux kernel 2.6.39.4. Any Ideas anyone?? Regards, Felix.

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