Re: ARM : Kernel : Setting up of MMU in head.S
Hi Prakash, On Wed, Mar 30, 2011 at 11:01 PM, Prakash K.B. prakash...@gmail.com wrote: Merci mate. :-) On Thu, Mar 31, 2011 at 3:59 AM, Dave Hylands dhyla...@gmail.com wrote: Hi Prakash, On Wed, Mar 30, 2011 at 2:35 PM, Dave Hylands dhyla...@gmail.com wrote: ...snip... When the MMU table is turned on, the PC is still at 0x800, so even though the kernel has 0xc00x mapped to 0x800x it also has to have 0x800x mapped to 0x800x. [Prakash] I think you meant to say So even though the kernel intends to map 0xc00 to 0x800XXX in the future, it has currently mapped 0x800xxx to 0x800xxx. No. the create_page_table function creates a page table which has 0x800x and 0xc00x both mapped to 0x800x. The one store intrustion saves the identity mapping (for 1 Mb) and the loop sets up the 0xc00x to 0x800x mapping. The identity portion is used as we discussed, and a few instructions after turning on the MMU, the CPU then does a jump from the 0x800x space to the 0xc00x space. After that, the identity mapping is no longer needed. Shortly after this, head.S calls into the start_kernel function (from init/main.c) and the paging_init function reinitializes the MMU removing the identity mapping. Now that I know this identity mapping is done on purpose, I hope to make good progress with the succeeding sequence. Do you confirm that only one entry is written into this L1 table because both mmu_enable and enable_mmu_end are on the same section? Yeah - essentially, that one mapping entry covers 1Mb of code space, which is sufficient to cover all of head.S, which is always at the front of the kernel image. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Debug Kernel Crash
Hello All, I wanted to know what is the best way to generate the kernel crash dump on kernel panic, after doing some searching, i came to know we can use kexec to load a new kernel on the kernel, i followed the instruction from the following links http://www.dedoimedo.com/computers/kdump.html http://www.developertutorials.com/tutorials/linux/reboot-linux-faster-072204-1358/ I do found that the kernel load properly with the, kexec -l option followed by kexec -e option, but when i set the kernel to be loaded on kernel panic using the option kexec -p, i see that after kernel crash, the system just hangs, it wont even try to load the new kernel. following are the commands am using. Can some one point, if there is any thing wrong with this. chkconfig kdump on /etc/init.d/kdump start kexec -l --append=`cat /proc/cmdline` --initrd=/boot/initrd.img-2.6.35.10-kdump /boot/vmlinuz-2.6.35.10-kdump kexec -e works fine and loads the kernel successfully, i will be able to see *starting new kernel* in the shell * * * chkconfig kdump on /etc/init.d/kdump start * kexec -p --append=`cat /proc/cmdline` --initrd=/boot/initrd.img-2.6.35.10* -kdump ** /boot/vmlinuz-2.6.35.10 -kdump * * * i simulate the panic by using echo 1 /proc/sys/kernel/sysrq echo c /proc/sysrq-trigger which just crash the kernel and system hangs, and it does not show any message *starting new kernel.* * * Thanks, ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: [virtual memory] page_table_lock mmap_sem
On 03/29/2011 06:30 PM, Venkatram Tummala wrote: Hi, Why do we need both page_table_lock mmap_sem in the kernel. Why isn't mmap_sem good enough for serialization. As far as i see it, all attempts to change the page table hierarchy in the kernel is done after holding the write lock on mmap_sem. As we are already holding the write lock, we do we need an extra page_table_lock (spinlock) ? Are there any code paths in the kernel which attempt to modify the page table hierarchy without holding the write lock on mmap_sem ? Yes, there are. Look at the page fault code, which takes a read lock on mmap_sem. This allows multiple threads in a multi-threaded process to handle page faults simultaneously. -- All rights reversed. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: ARM : Kernel : Setting up of MMU in head.S
Merci mate. :-) On Thu, Mar 31, 2011 at 3:59 AM, Dave Hylands dhyla...@gmail.com wrote: Hi Prakash, On Wed, Mar 30, 2011 at 2:35 PM, Dave Hylands dhyla...@gmail.com wrote: Hi Prakash, On Wed, Mar 30, 2011 at 8:19 AM, Prakash K.B. prakash...@gmail.com wrote: Hello. Please do not hesitate to let me know if this must be posted elsewhere. I have been trying to understand the code that sets up the MMU. I do have a fair understanding of the way MMU is meant to be setup, but something in the kernel code is tripping me. Some further explanation is due. When the kernel starts, the MMU is off, and ther ARM is running with an implicit identity mapping (i.e. each virtual address maps to the same physical address). [Prakash] Aha...So what I ignored as a routine code comment had a deeper meaning.. :-) If your physical memory starts at 0x8000, then the PC will be 0x800x. [Prakash] Agreed. When the MMU table is turned on, the PC is still at 0x800, so even though the kernel has 0xc00x mapped to 0x800x it also has to have 0x800x mapped to 0x800x. [Prakash] I think you meant to say So even though the kernel intends to map 0xc00 to 0x800XXX in the future, it has currently mapped 0x800xxx to 0x800xxx. Now that I know this identity mapping is done on purpose, I hope to make good progress with the succeeding sequence. Do you confirm that only one entry is written into this L1 table because both mmu_enable and enable_mmu_end are on the same section? So this mapping of 0x800x to 0x800x is the identity portion and is needed while switching the MMU on. The 0xc00x to 0x800x mapping is what's used while the kernel is running. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com -Prakash ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Debug Kernel Crash
kernel. following are the commands am using. Can some one point, if there is any thing wrong with this. chkconfig kdump on /etc/init.d/kdump start kexec -l --append=`cat /proc/cmdline` --initrd=/boot/initrd.img-2.6.35.10-kdump /boot/vmlinuz-2.6.35.10-kdump kexec -e works fine and loads the kernel successfully, i will be able to see starting new kernel in the shell chkconfig kdump on /etc/init.d/kdump start kexec -p --append=`cat /proc/cmdline` --initrd=/boot/initrd.img-2.6.35.10 -kdump /boot/vmlinuz-2.6.35.10 -kdump i simulate the panic by using echo 1 /proc/sys/kernel/sysrq echo c /proc/sysrq-trigger which just crash the kernel and system hangs, and it does not show any message starting new kernel. does /var/crash or kdump target directory as mentioned in /etc/kdump.conf exists? sometime it may be a while before it starts to dump if memory on machine is huge and you have set kdump level to dump everything. thx,thayumanavar s. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: mapping address pointer to page structure
On Wed, Mar 30, 2011 at 10:42 PM, sk.syed2 sk.sy...@gmail.com wrote: struct page *page = virt_to_page(skb-data); int offset = (unsigned long) skb-data - (unsigned long) page_address(page); skb_add_rx_frag(master_skb, skb_shinfo(master_skb)-nr_frags, page, offset, skb-len) . . is this the right way to do ? This will work if skb-len PAGE_SIZE, otherwise it means it spans more than a page and you need to do skb_add_rx_frag for each PAGE_SIZE data present. Refer to Understanding Linux network internals By Christian Benvenuti p 488/489. Thanks Syed, skb-len is always smaller then PAGE_SIZE because i have set the mtu size as 1500 from my network driver. But am facing kernel panic, if i just the moment the driver call dev_queue_xmit, so i guess this may not be right way to get the page. Anyways thanks for the support. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Snooping on sockets/file descriptors
Hi, Is it possible for an application (say snoop, with sufficient privileges) to monitor data on any socket/file descriptor in the system? Here's an example: suppose we have a browser and it creates a tcp socket to connect to a URL. Whenever the browser issues a read() and data is pushed to user space, I want snoop to get notified and made available a copy of the same data that the browser read. ptrace can be used to do it, but then there are several ways the app can read data. It could use read(), or recv() or recvmsg(). Is there a better way to deal with this complexity? It's like the action of tee on any socket/file descriptor in the system. -- Vimal ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Snooping on sockets/file descriptors
On Thu, Mar 31, 2011 at 10:29 PM, Vimal j.vi...@gmail.com wrote: Hi, Is it possible for an application (say snoop, with sufficient privileges) to monitor data on any socket/file descriptor in the system? Here's an example: suppose we have a browser and it creates a tcp socket to connect to a URL. Whenever the browser issues a read() and data is pushed to user space, I want snoop to get notified and made available a copy of the same data that the browser read. ptrace can be used to do it, but then there are several ways the app can read data. It could use read(), or recv() or recvmsg(). Is there a better way to deal with this complexity? It's like the action of tee on any socket/file descriptor in the system. How about tcpdump? thanks, Daniel. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Snooping on sockets/file descriptors
Hi Daniel, How about tcpdump? Thanks for the suggestion. tcpdump is good, but it doesn't solve all problems. There are a few reasons: * TCP packets could arrive out of order * The data needn't belong to a valid TCP connection * The app could just discard data (close/flush/etc) In short, there is a lot of state and complex logic which act on the packets before it is seen by the application. Given the complexity (such as wide variations in TCP implementation), I am not sure if reimplementing them is a good idea, even if it's possible. Thanks, -- Vimal ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Snooping on sockets/file descriptors
On Fri, Apr 1, 2011 at 03:04, Vimal j.vi...@gmail.com wrote: Hi Daniel, How about tcpdump? Thanks for the suggestion. tcpdump is good, but it doesn't solve all problems. There are a few reasons: * TCP packets could arrive out of order * The data needn't belong to a valid TCP connection * The app could just discard data (close/flush/etc) In short, there is a lot of state and complex logic which act on the packets before it is seen by the application. then, something like dtrace or systemtap? IMO you're looking for kinda combo of kernel mode + user land sniffer... the user land sniffer, in it's very simple form, is by using LD_PRELOAD ... -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Requirement of Linux port
Hi All, Is there any document on web summarized the hardware (especially, CPU) that a Linux depends on. For example, if a CPU doesn't support misaligned access (no exception will be generated when misalignment access), can Linux run on that? Thanks. BR, Jacky ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Debug Kernel Crash
Hi, does /var/crash or kdump target directory as mentioned in /etc/kdump.conf exists? One thing i forgot to mention is in my root there is not configuration file /etc/sysconfig/kdump or /etc/kdump.conf, is this anything to do with this and not even /var/crash, i got the latest kexec-tool source from the git and build it. sometime it may be a while before it starts to dump if memory on machine is huge and i almost left my system for an hour, but it was in the same hang state. you have set kdump level to dump everything. Where else can be the configuration file other then /etc/sysconfig/kdump or /etc/kdump.conf. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Requirement of Linux port
Hi! On 11:30 Fri 01 Apr , Jacky Lam wrote: Hi All, Is there any document on web summarized the hardware (especially, CPU) that a Linux depends on. For example, if a CPU doesn't support misaligned access (no exception will be generated when misalignment access), can Linux run on that? I do not know of such a document, but I have not looked for one so far. But basically: - CPUs which do not support misaligned access are supported. - CPUs less than 32 bit are not supported. When compiling with gcc, int is always 32 bit, long is 32/64 bit (depending on 32/64 bit CPU) and long long is always 64 bit. You can also use __u8 __u16 __u32 __u64 __s8 __s16 __s32 and __s64, if you want to. - Both big endian and little endian is supported. The interesting stuff starts if you want to port a program to/from other OSes. Then you have to take care of missing libs/syscalls (like I/O multiplexer and a lot of GUIs stuff) or syscalls which behave differently (like fsync())... -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
