February 2011 - kernelnewbies@kernelnewbies.org

Regarding Buddy Allocator
by Sri Ram Vemulpali Feb. 8, 2011

Feb. 8, 2011

Can anyone point me to implementation of buddy allocator, with efficient data structures used. Thanks in advance. I am trying to get another thought or implementation on code. -- Regards, Sri.

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Another ISP1761 / FTDI / serial problem
by Arvid Brodin Feb. 8, 2011

Feb. 8, 2011

Hi! I get weird problems when I use a null modem cable between the two ports on a FT232BM (2-port FTDI USB-to-serial converter) with an isp1761 host controller. The same thing does not happen with an EHCI host controller. Lengthy details follows: With the EHCI host controller: ============================= [Terminal 1] $ cat /dev/ttyUSB1 [Terminal 2] $ echo "Something seems wrong here" > /dev/ttyUSB0 $ echo "Something seems wrong here" > /dev/ttyUSB0 [Terminal 1] Something seems wrong here Something seems wrong here ^C $ Observe the extra new line after the strings. I'm not sure if this is a bug in the ftdi driver, some other part of the serial subsystem, or if it is the result of some terminal setting; with a USB analyzer I observe the following sequence of packets (#-# == device-endpoint): 3-2 OUT: "Something seems wrong here" 3-2 OUT: 0x0D 0x0A 4-1 IN: 0x01 0x60 'S' 4-1 IN: 0x01 0x60 'o' ... 4-1 IN: 0x01 0x60 0x0D 4-1 IN: 0x01 0x60 0x0A 4-2 OUT: 'S' # The echo from the reading side starts here 4-2 OUT: 'o' ... 4-2 OUT: 0x0D 0x0A 4-2 OUT: 0x0D 0x0A # The newline pair is echoed twice - perhaps both 'CR' and 'NL' are converted to "CRNL" in the echo? Anyway, since 3-1 is never read, no feedback loop is created by the two echoing devices. With the isp1761 host controller, driver from 2.6.35.7 backported to 2.6.27.54 and modified for platform endianness: ============================= [Terminal 1] $ cat /dev/ttyUSB1 [Terminal 2] # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 [Terminal 1] This is isp1761 and something is wrong This is isp1761 and something is wrong This is isp1761 and something is wrong This is isp1761 and something is wrong This is isp1761 and something is wrong and something is wrong (blank line x7) This is isp1761 and something is wrong ^C # echo "This is isp1761 and something is wrong" > /dev/ttyUSB0 # cat /dev/ttyUSB1 is wrong (blank line x30 ca) TThis is isp1761 and something is wrong ^C # The exact look of the error differs, but it is quite easy to trigger by echoing text several times in a row; also breaking the "cat" execution, echoing some more text, and then starting cat again seems to trigger the error often. On the bus the traffic looks something like this: 7-2 OUT: "This is isp1761 and something is wrong" 7-2 OUT: 0x0D 7-2 OUT: 0x0A (NAK) # The CRNL pair is split here and the NL is not directly accepted by the device 7-2 OUT: 0x0A (NAK) Following this is lots and lots of "0x0A NAKs" intermixed with traffic that looks quite like the EHCI case except that much of the traffic has to be re-sent lots of times before it is accepted. The 0x0A is finally accepted after all text has been received by 8-1 and echoed from 8-2. This exact pattern is repeated every time text is written to the serial port. Device 8 receives the characters and echoes them back to 7-1 as in the EHCI case. But with isp1761, after a while device 7 for some reason starts echoing parts of the received echo-text back. My guess is that this should not happen since device 7 is never read from. Anyway, this creates a feedback loop which would be the source of the spurious characters in the "cat" run above and that sometimes is powerful enough to make the terminal unresponsible. I've been trying to figure this thing out for a while now but quite frankly I'm stumped; I can't figure out where and why things goes wrong. Any ideas are welcome! Perhaps the NAK problem/bug triggers a problem/bug somewhere in linux' serial terminal code? The terminal settings are the defaults and are the same during all examples above on both serial ports: $ stty -a -F /dev/ttyUSB0 speed 9600 baud; rows 0; columns 0; line = 0; intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0; -parenb -parodd cs8 hupcl -cstopb cread clocal -crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel -iutf8 opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke $ stty -g -F /dev/ttyUSB0 500:5:cbd:8a3b:3:1c:7f:15:4:0:1:0:11:13:1a:0:12:f:17:16:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0 -- Arvid Brodin Enea Services Stockholm AB

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Re: page size change on MIPS
by Mulyadi Santosa Feb. 8, 2011

Feb. 8, 2011

Hi... On Tue, Feb 8, 2011 at 14:35, naveen yadav <yad.naveen(a)gmail.com> wrote: > Hi All, > > I debug this issue further, I check in kernel File name is > binfmt_elf.c and function name is create_elf_tables() > > I put a debug print here to check what kernel is reading from user space. > > if (__put_user((elf_addr_t)p, argv++)) > return -EFAULT; > len = strnlen_user((void __user *)p, MAX_ARG_STRLEN); > printk("\n Lenght of arg=%ld,%s \n",len,(void __user *)p); > if (!len || len > MAX_ARG_STRLEN) > return -EINVAL; > p += len; > } > > > when Page size is 16KB o/p is > > Lenght of arg=6,/init > > when Page size is 64KB o/p is > > Lenght of arg=1, > > so I got null when it read from ELF hum? very strange.... so essentially it can't read...or to be precise, properly read command arguments (including the executable name itself)? maybe the problem lies somewhere in the initrd/initramfs? -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

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DMA to Userspace
by Nikolaus Rath Feb. 8, 2011

Feb. 8, 2011

Hello, I am trying to make a DMA transfer from userspace. My code looks like this (data.vi_buf is a pointer to the userspace address): down_read(&current->mm->mmap_sem); rc = get_user_pages(current, current->mm, (unsigned long) data.vi_buf, 1, 1, 0, &acq_dev->vi_pg, NULL); up_read(&current->mm->mmap_sem); if (rc != 1) { err("get_user_pages failed for VI."); return -EINVAL; } acq_dev->vi_d = dma_map_page(dev, acq_dev->vi_pg, 0, PAGE_SIZE, DMA_TO_DEVICE); if (acq_dev->vi_d == 0) { err("dma_map_page failed for VI."); goto cleanup_vi_2; } info("VI bus address: 0x%0lx", (unsigned long) acq_dev->vi_d); But when my PCI device then reads data from the bus address acq_dev->vi_d, it just gets \0 bytes rather then the contents of the acq_dev->userspace buffer. I tried to debug this with an additional info("VI Start: 0x%0x", ((uint32_t*) page_address(acq_dev->vi_pg))[0]); to print out the first byte of the mapped page, but this actually results in a kernel crash: BUG: unable to handle kernel NULL pointer dereference at (null) Can anyone tell why my debugging idea does not work? And does anyone have a suggestion how I could better debug my original problem? Thanks, -Nikolaus -- »Time flies like an arrow, fruit flies like a Banana.« PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6 02CF A9AD B7F8 AE4E 425C

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kernel idle fucntion......
by Murali N Feb. 7, 2011

Feb. 7, 2011

Hi, I have one basic doubt on kernel idle function. Who called the kernel cpu_idle function? I know a theory that it gets called when there is no activity in the system? Here i have the following question. 1. How cpu knows that there is nothing to be left out to run? scheduler get to know this by looking the RUN queue? Also in 'kernel/arch/arm/process.c' file i saw a variable called 'hlt_counter', what exactly is this variable? Can somebody share your thoughts on this -- Regards, Murali N

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When "probe" is called?
by Joy Sun Feb. 7, 2011

Feb. 7, 2011

Hi, I am seeing probe function pointer and know the procedure to register of it for a specific device driver. However, I wonder when it is actually called? For example, for platform drivers, there is a structure like this: struct platform_driver { int (*probe)(struct platform_device *); int (*remove)(struct platform_device *); void (*shutdown)(struct platform_device *); int (*suspend)(struct platform_device *, pm_message_t state); int (*suspend_late)(struct platform_device *, pm_message_t state); int (*resume_early)(struct platform_device *); int (*resume)(struct platform_device *); struct device_driver driver; }; Then, it is registered by int platform_driver_register(struct platform_driver *drv); But, I wonder when actually, those functions (especially, probe) are called. Could you guide me about it, please? Thanks, -J.

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What is __init?
by Joy Sun Feb. 7, 2011

Feb. 7, 2011

Hi, I am totally newbie for kernel device driver, and starting to learn. When I see a driver code, I found __init. For example, static int __init xxxx(struct platform_device *pdev) I understand "static" and "int", but what is __init? -J.

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Fwd: storing the logs
by mohit verma Feb. 6, 2011

Feb. 6, 2011

thanks greg,, a silly question......please have a look....... i create a socket to communicate to the user space app to listen to and responsible for loggin ... via my_sock=netlink_creat_sock() i create my own logging message format to send it via netlink interface. then how can i let my module know which process to bind it to? i mean to bind my socket to any user space application i need the pid of that one ,so at the very first time how can i initialize the binding process with user space application? i hope.. i am clear to u. please let me know if not....i wll try again. i 'd really appreciate any help. -- ........................ *MOHIT VERMA*

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netlink interface
by mohit verma Feb. 6, 2011

Feb. 6, 2011

hi folks, if i add a new event notifier for netlink interface ( that is by adding a macro in netlink.h header file and defining it elsewhere) and make use of klogd to handle the log messages generated by module to syslogd (or to syslog-ng) then as i have added a new socket type ( event-notifier) into kernel so how can i make syslog api come to know that the perticular socket to be inspected also? i mean when the kernel emitts the messages having new_socket type then how can i configure the klogd or syslog-api to succesfully catch these messages ?? thanks a lot in advance . -- ........................ *MOHIT VERMA*

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Introduction
by Ian Porter Feb. 5, 2011

Feb. 5, 2011

HI All, My name is Ian Porter and I have done a couple of changes to the kernel to make the laptop work with 4GB of memory, and I would like to learn more about the kernel and hopefully this is a good place to learn and ask questions :). -- Kind regards Ian Porter www: www.codingfriends.com

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