May 2014 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

LKM related API documentation
by Abhijeet Kasurde May 4, 2014

May 4, 2014

Hi All, Can anyone point me to any location of documentation related to Linux Kernel Module APIs ? I am specifically looking for following APIs - 1. find_symbol 2. request_module 3. find_module etc. Thanks in advance.

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Regarding skb and net_device.
by Pranay Srivastava May 4, 2014

May 4, 2014

Hi, This is probably a stupid question, but i'm not able to find the answer. How does the networking subsystem decides which device to use for sending the skb. Can some one please guide me to the particular code. I seem to get lost in there :( -- ---P.K.S

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Question Regarding vm_area_struct
by Pranay Srivastava May 3, 2014

May 3, 2014

Hi, I'm trying to mmap a device's memory (not real device) and share it across processes. So far what I've understood is that, 1. I create a vm_operations_struct->fault and vm_operations_struct->page_mkwrite 2. The first time a fault occurs my fault handler would allocate a page and install it in the vm_fault structure. The corresponding vm_area_struct i'll mark as VM_SHARED|VM_READ. Should VM_SHARED be really set here? I'm sharing the page not the vm_area_struct. 3. On a fault I can just assign the same page and in page_mkwrite i can check if there's someone already writing to the page and tell other process that it has to wait or throw error that page can't be made writeable as of now. 4. vm_operations_struct->close, to have a put_page call. Question 1 Let's just say if each vma had to be allocated a page individually, that page would have been allocated using GFP_HIGHUSER|GFP_USER. In that case would the module needed to have kept track of the pages or when the process exits the page structure would be in same state as the last call to put_page? Question 2 If a process unmaps or just exits the unmap_vmas would be called which would call unmap_single_vmas. Now I haven't digged too much within that but it plays around with pte of the page but doesn't alter page_count or anything. So would that affect the other process's vmas which are sharing this page? I'm referring to zap_pte_range, but it seems to flush tlbs and not remove the pte actually[Correct?]. Since the same code would be used for page cache pages and their pte won't be removed in case they are low-mem pages. So if let's say somebody tries to access that particular address it'll not fault although the process owning it has exited? -- ---P.K.S

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MPC8640D Linux booting Process
by curieux.khetan＠gmail.com May 3, 2014

May 3, 2014

Hi, I have MPC8640D based custom designed board and ported Linux 3.14 successfully. Now I have enabled core1 and facing some issues. when I run smp Linux on it, its booting fine but whenever I am trying to use Ethernet on tsec2, tsec3, or tsec4 its getting panic. Any suggestion/pointer how to get more details why its panic? because while only running core0 all Ethernet ports are working fine. And how to run ASMP Linux on this board from u-boot? Thanks & Regards @$hi$h

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RE: MPC8641 based custom board Kernel stuck at 1000Mhz core clock
by curieux.khetan＠gmail.com May 3, 2014

May 3, 2014

hi thanks for your reply. the problem is still there. At 800MHZ core its working fine but for 1Ghz its still happening. Any suggestion or check point I can monitor. From: sanjeev sharma Sent: ‎02‎ ‎May‎ ‎2014 ‎09‎:‎22 To: Ashish CC: Valdis Kletnieks; scottwood(a)freescale.com; linuxppc-dev(a)lists.ozlabs.org; kernelnewbies Subject: Re: MPC8641 based custom board Kernel stuck at 1000Mhz core clock Hello Ashish, is this issue resolved and is this always happening when you are changing core to 1Ghz because i am confused here with sometime Keyword. Regards Sanjeev Sharma On Fri, Apr 4, 2014 at 1:12 PM, Ashish <curieux.khetan(a)gmail.com> wrote: On Thursday 03 April 2014 08:55 AM, sanjeev sharma wrote: Are you able to capture kernel logs ? Regards Sanjeev Sharma On Thu, Mar 27, 2014 at 10:01 PM, <Valdis.Kletnieks(a)vt.edu> wrote: On Thu, 27 Mar 2014 16:04:37 +0530, Ashish said: > Hi, > > I am using MPC8641-HPCN based custom board and able to boot linux at > MPX clock 400Mhz and core clock 800mhz. When I am increasing core > frequency ie MPX clock at 400Mhz and core at 1Ghz, kernel stuck. Step 0: Prove to us that your core actually runs reliable and stably at 1Ghz. Step 1: Figure out *where* it gets stuck. If you have earlyprintk working on your board, adding 'initcall_debug ignore_loglevel' to the kernel cmdline often helps track down where a kernel hangs during boot. _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies Hi, Does kernel logs means debugging information that kernel prints while booting using printk or it is something else? Here is kernel boot logs that kernel printed while booting... U-Boot 2013.04 (Jan 27 2014 - 11:21:21) Unicore software on multiprocessor system!! To enable mutlticore build define CONFIG_MP CPU: 8641, Version: 2.1, (0x80900021) Core: E600 Core 0, Version: 2.2, (0x80040202) Clock Configuration: CPU:1000 MHz, MPX:400 MHz DDR:200 MHz (400 MT/s data rate), LBC:25 MHz L1: D-cache 32 KB enabled I-cache 32 KB enabled L2: 512 KB enabled Board: MPC8641-HPCN I2C: ready DRAM: 512 MiB SDRAM test phase 1: SDRAM test phase 2: SDRAM test passed. Flash: 16 MiB EEPROM: NXID v1 In: serial Out: serial Err: serial Net: eTSEC1, eTSEC2, eTSEC3, eTSEC4 [PRIME] Hit any key to stop autoboot: Speed: 1000, full duplex Using eTSEC4 device TFTP from server 192.168.10.1; our IP address is 192.168.10.2 Filename 'uRamdisk'. Load address: 0x600000 Loading: * ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################## 13.1 MiB/s done Bytes transferred = 22680188 (15a127c hex) Speed: 1000, full duplex Using eTSEC4 device TFTP from server 192.168.10.1; our IP address is 192.168.10.2 Filename 'uImage'. Load address: 0x16000000 Loading: * ################################################################# ################################################################# ####################################### 14 MiB/s done Bytes transferred = 2476304 (25c910 hex) Speed: 1000, full duplex Using eTSEC4 device TFTP from server 192.168.10.1; our IP address is 192.168.10.2 Filename 'mpc8641_hpcn.dtb'. Load address: 0x14000000 Loading: * # 2.6 MiB/s done Bytes transferred = 5540 (15a4 hex) ## Booting kernel from Legacy Image at 16000000 ... Image Name: Linux-3.13.6 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 2476240 Bytes = 2.4 MiB Load Address: 00000000 Entry Point: 00000000 Verifying Checksum ... OK ## Loading init Ramdisk from Legacy Image at 00600000 ... Image Name: rootfs Image Type: PowerPC Linux RAMDisk Image (gzip compressed) Data Size: 22680124 Bytes = 21.6 MiB Load Address: 00000000 Entry Point: 00000000 Verifying Checksum ... OK ## Flattened Device Tree blob at 14000000 Booting using the fdt blob at 0x14000000 Uncompressing Kernel Image ... OK Loading Ramdisk to 1e923000, end 1fec423c ... OK Loading Device Tree to 007fb000, end 007ff5a3 ... OK (some times it stucking here) Using MPC86xx HPCN machine description Total memory = 512MB; using 1024kB for hash table (at cff00000) Linux version 3.13.6 (ashish@ashish-VirtualBox) (gcc version 4.7.2 (GCC) ) #8 Sat Mar 29 10:31:58 IST 2014 Found initrd at 0xde923000:0xdfec423c bootconsole [udbg0] enabled setup_arch: bootmem mpc86xx_hpcn_setup_arch() MPC86xx HPCN board from Freescale Semiconductor arch: exit Zone ranges: DMA [mem 0x00000000-0x1fffffff] Normal empty HighMem empty Movable zone start for each node Early memory node ranges node 0: [mem 0x00000000-0x1fffffff] (some times here)

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Regarding net_device_ops
by Pranay Srivastava May 3, 2014

May 3, 2014

Hi Referring to Documentation/networking/netdevices.txt a) ndo->ndo_start_xmit if written "as is" will be thread safe? [Correct?] NETIF_F_LLTX is not set only then this is true. But dev_queue_xmit(skb) doesn't seem to take any lock, neither does dev_hard_start_xmit. Please let me know if i'm wrong and where is this lock taken before calling dev_queue_xmit/dev_hard_start_xmit. b) Why and when would I want to use rtnl_lock/unlock? Is it like registering multiple device simultaneously? c) ndo->ndo_start_xmit is supposed to start the transmission of the skb. However I've a doubt ---> Suppose that there's no room left for the incoming skb in the device buffer, so in that case it would be ideal to call netif_stop_queue. At this the the skb already with the ndo_start_xmit will not be retried again[Correct?] ----> Is ndo_start_xmit required to wait in this case? However if the above spin_lock in a) was taken then this would be a waste. So is it possible that this skb is "deffered" to whenever there's room and return NETDEV_TX_OK? But if we do this we are telling the application that it's packet was delivered so in case there was a timeout set by the application on a reply it would again send us the same packet. So instead of "deferring" is it good to "drop" ? -- ---P.K.S

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Re: Linux Interrupt Context maps to ARM CPSR.mode = IRQ
by Mj Embd May 2, 2014

May 2, 2014

On Fri, May 2, 2014 at 7:17 PM, Marc Zyngier <marc.zyngier(a)arm.com> wrote: > On 2014-05-02 13:34, Mj Embd wrote: >> >> Adding Marc to comment >> Marc Please clarify the doubt >> >> >> >> On Fri, May 2, 2014 at 5:15 PM, Mj Embd <mj.embd(a)gmail.com> wrote: >>> >>> Hi, >>> >>> As per a lot of linux documentation some components work in process >>> context and some work in interrupt context. >>> >>> If we try to map these contexts to ARM processor modes then is it >>> safely to assume that >>> Process Context : CPSR.mode = SVC >>> Interrupt Context : CPSR.mode = IRQ >>> >>> If not how to define interrupt context properly. Confusing at times. > > > Well, none of this is completely true. > > Process context exists both in USR (process in user mode) and SVC (process > in kernel mode, executing a syscall for example). > > As for interrupts, the processor indeed starts executing the interrupt in > IRQ mode, but this is a useless complication as far as Linux is concerned, I didn't understood the term useless here, I hope it is not about the question itself. > and we quickly switch to SVC (see the definition of the vector_stub macro in > arch/arm/kernel/entry-armv.S). > So what is the mode of the processor when Linux is executing in the Academic / Bookish Term "Interrupt Context" There is a function called in_interrupt which tells if linux is in interrupt context. But How to define/quantify Interrupt Context as a whole Also, Some texts say there are two contexts Hard IRQ Context , Soft IRQ Context. HardIRQ = interrupts Disabled , (possibly CPSR.I=1, mode=IRQ) SoftIRQ = interrupts Enabled , (possibly CPSR.I=0, mode=IRQ) SoftIRQs when executed from Ksoftirqd daemon (possibly CPSR.I=0, mode=SVC) We have a client query on this. > Hope this helps. > > M. > -- > Fast, cheap, reliable. Pick two. -- -mj

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Linux Interrupt Context maps to ARM CPSR.mode = IRQ
by Mj Embd May 2, 2014

May 2, 2014

Hi, As per a lot of linux documentation some components work in process context and some work in interrupt context. If we try to map these contexts to ARM processor modes then is it safely to assume that Process Context : CPSR.mode = SVC Interrupt Context : CPSR.mode = IRQ If not how to define interrupt context properly. Confusing at times. -- -mj

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system call returns -1
by Nada Saif May 2, 2014

May 2, 2014

Hi, I added a new system call to kernel 2.6.32.61 - I used these commands for complication : make oldconfig make make modules install It went ok with few warning messages. When I tried to test the system call , the function _syscall return -1, what that means? Thanks, Nada

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Question about VFS
by Adam Fowler May 2, 2014

May 2, 2014

I've been trying to implement a file system using vfs and I've got mkdir and touch working but I can't seem to get echo blah > new file to create a new file with content blah. I tried to use printk to see what gets called during the creation process but it doesn't seem that write is getting called for my file, just open. When I ran strace I see a write call but it is to stdout and not to my file. Any tips on how to go about implementing the behavior I'm after? I've been following the following tutorial with the changes necessary to work on kernel 3.10.34 http://lwn.net/Articles/57369/ . Any help is appreciated, thanks! -- Adam Fowler<ajf2177(a)columbia.edu>

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