March 2013 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

How to get the inode - no path_lookup
by Rishi Agrawal Sept. 17, 2015

Sept. 17, 2015

Hi All, I had a module which used the path_lookup function to print the details of any file's inode. I now want to rewrite that module in order to show some juniors how to write some code in kernel. I am using 3.4.6 kernel, I tried finding out path_lookup but google showed that it has been removed. I tried the following code then which did not work . . . dentry = kern_path_create(AT_FDCWD, filename, &path, 1); if (IS_ERR(dentry)) { printk("Failed to obtain the dentry"); return; } its not returning dentry I again tried after seeing the implementation of vfs_stat function user_path_at(AT_FDCWD, filename, lookup_flags, &path); but this also fails. I am using a proc interface to pass the filename, and copying the filename into a kernel buffer. How can I get a copy of vfs inode for a file name. -- Regards, Rishi Agrawal

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How kernel handle interrupts
by Woody Wu Aug. 5, 2013

Aug. 5, 2013

Hi, List Where is the Kernel code that handles external interrupts? I want to have a look at it but haven't found out where it is. Actually, I have some basic questions about interrupt handling in Linux. 1. After Kernel's ISR received an interrupt, I believe it will invoke a handler defined in a device driver if any. But it should be the device driver's responsibility or kernel ISR's responsibility to clear (or acknowledge) the interrupt? 2. My device, an AX88796B network controller, asserting the interrupt line in a level-triggered manner. Now I met problem with the device that might caused by the CPU interrupt mode is not set as level-triggered by edge trigger. My CPU is Samsung S3C2410, an ARM920T powered one. Does anyone know usually where and how should I do this kind of setting? Thanks in advance. -- woody I can't go back to yesterday - because I was a different person then.

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linux segment
by Fan Yang June 20, 2013

June 20, 2013

Hi all: I print the cs ds and ss register in the user space, and it is same as the __USER_CS and __USER_DS which defined in kernel as 73 and 7b. In the kernel __KERNEL_CS and __KERNEL_DS defined as 60 and 68, but when I print this two value in my kernel module, I get 60 and 7b. Why ? It should be 60 and 68, shouldn't it?

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[help] kernel oops in function gpio_to_irq
by Mylene Josserand April 3, 2013

April 3, 2013

Hi everyone, I have a problem with gpio functions. My kernel version is 3.8.2 and my SoC is a imX27 on a "home-made" board. First, when I boot, I had only the "Starting kernel..." message. So I rebuild my kernel with CONFIG_DEBUG_KERNEL, CONFIG_DEBUG_LL and CONFIG_EARLY_PRINTK. I have also add the line "earlyprintk=console,UART0,115200" on the bootargs of my Barebox. With that, I can see more messages : [...] Unable to handle kernel NULL pointer dereference at virtual address 0000002c pgd = c0004000 [0000002c] *pgd=00000000 Internal error: Oops: 5 [#1] PREEMPT ARM Modules linked in: CPU: 0 Not tainted (3.8.2+ #4) PC is at __gpio_to_irq+0x1c/0x44 LR is at navocap_baseboard_init+0xd8/0x2c8 pc : [<c01fd194>] lr : [<c04fd468>] psr: 60000053 sp : c7835ef0 ip : 00000079 fp : c05a5628 r10: c04f817c r9 : 00000000 r8 : c05a562c r7 : c7834000 r6 : 00000004 r5 : c05158c4 r4 : c0578844 r3 : 000005ac r2 : c05b0410 r1 : c7834000 r0 : 00000000 Flags: nZCv IRQs on FIQs off Mode SVC_32 ISA ARM Segment kernel Control: 0005317f Table: a0004000 DAC: 00000017 Process swapper (pid: 1, stack limit = 0xc78341b8) Stack: (0xc7835ef0 to 0xc7836000) 5ee0: c05158c4 c04fd468 00000002 10009000 5f00: 10009fff 00000000 00000200 00000000 00000000 00000000 c05158c4 c04fd348 5f20: c0578844 c04f819c c04d23dc c00087f8 00000003 00000003 c04d1b2c c06bd6a0 5f40: 00000000 c0578844 c05158c4 00000004 0000008b c05a562c c0515898 c04f6378 5f60: c05a5620 c04f62a0 00000003 00000003 c04f6378 c00403e0 00000000 00000000 5f80: c03cfee0 00000000 00000000 00000000 00000000 00000000 00000000 c03cfeec 5fa0: 00000000 00000000 c03cfee0 c00093b0 00000000 00000000 00000000 00000000 5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 5fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00100000 000a1000 [<c01fd194>] (__gpio_to_irq+0x1c/0x44) from [<c04fd468>] (navocap_baseboard_init+0xd8/0x2c8) [<c04fd468>] (navocap_baseboard_init+0xd8/0x2c8) from [<c04f819c>] (customize_machine+0x20/0x30) [<c04f819c>] (customize_machine+0x20/0x30) from [<c00087f8>] (do_one_initcall+0x2c/0x168) [<c00087f8>] (do_one_initcall+0x2c/0x168) from [<c04f62a0>] (kernel_init_freeable+0xf4/0x1cc) [<c04f62a0>] (kernel_init_freeable+0xf4/0x1cc) from [<c03cfeec>] (kernel_init+0xc/0x164) [<c03cfeec>] (kernel_init+0xc/0x164) from [<c00093b0>] (ret_from_fork+0x14/0x24) Code: e0433100 e1a0c000 e7920003 e24dd004 (e590302c) ---[ end trace 61bb09c25216d85b ]--- Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b The problem is in the function "gpio_to_irq" in my board init functions (navocap_baseboard_init). To know which lines the opps appears, I have followed this tutorial : https://wiki.ubuntu.com/Kernel/KernelDebuggingTricks Thanks to it, I can notice that the opps appears when I called the "gpio_to_irq" function in : ret = request_irq(gpio_to_irq(IMX_GPIO_NR(2,14)), detect_irq, IRQF_TRIGGER_FALLING, "imx-mmc-detect", data); I have checked in other boards how to use this function and it is configured in the same way. I did see where I have made a mistake. Maybe in my config file where I have missed a configuration option ? How to solve this opps problem ? It would be very great if someone could give me some helps / feedbacks on this problem. Thank you in advance ! Best regards, -- Mylène JOSSERAND Navocap

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Online migration of arbitrary filesystems, possible?
by Daniel Hilst April 2, 2013

April 2, 2013

Suppose that I have two big filesystems, dest fs and source fs.. I want to copy whole source fs to dest fs, but I need to keep source filesystem online I can't mount source fs read only and copy.. The idea is, mount both filesystems "together", and make write/read operations go on this way Read operations: 1. See if data is already on dest fs, 2. If is then read data and bright back to caller (lets call this cold read) 3. If is not, then read file from source fs, put it on page cache, and change the backstorage of that page.. 3.1 So when this page get dirty or too old, it will be writed to dest fs The problem here is, I need to remap every data and metadata on step 3 (inodes and stuff), I think that read only data, isn't writed to disk, so in case of old page, this page would be freed from memory and not write to dest fs.. so I need read only pages to be forced dirty.. Write operations: 1. Write data to dest fs 2. Mark data as present on dest fs Also I need to know when copy is finished, so I need a tool to crosscheck both filesystems and say what was copied and what wasn't, and give me some percent of remaining unsynced data. When I get 100% of data in sync I can umount source filesystem and use its storage for other propose. The go here is move data online, where I can't bring data offline.. I'm a kernel newbie, I have just read a lot about page cache and VSF, but this seems possible, right? -- Follow the white rabbit!

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pci_alloc_consistent doubt
by Dhananjay Maske April 1, 2013

April 1, 2013

Hi All, I am fairly New to Linux kernel Programming and i have few questions with respect to pci_alloc_consistent . 1) as we know pci_alloc_consistent allocates dma buffers which is visible to DMA controller as well as CPU. virt_add = pci_alloc_consistent(pdev, size, dma_addr_t bus_adrr); here it will allocate a buffer and return its virtual address and corresponding bus address. My question is do these two address ultimately point to similar location but from different perspectives ?. 2) After allocating these address, how do we proceed given that i have a ASIC register which has the dma_rx_desc_start address ? 3) Also does all the HW's which support dma have the descriptor data structures by provided by Vender or is there any specific format that dev has to be aware of for designing such descriptor for that particular driver ?

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Signal handlers
by Rahul Gandhi March 31, 2013

March 31, 2013

Hey! I am still a newbie to kernel development. I was reading about signals and signal handlers. The signal function describe as follows: sighandler_t *signal* (int signum, sighandler_t action) As per my understanding, when the signal denoted by signum occurs/is raised, the action is taken which can be either SIG_DFL, SIG_IGN or a function/handler. What i don't understand is, when we write for example signal(SIGPROF, handler); isn't this supposed to be asynchronous? however the code is executed sequentially. So, when this function is encountered, it is executed and when a signal is raised, how does it know what to do? This might sound foolish, bear with me. Thanks Rahul Gandhi

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Re: extended asm and register clobbers
by ishare March 31, 2013

March 31, 2013

On Sat, Mar 30, 2013 at 02:04:04PM -0700, dw wrote: > I read this line from the docs: > > "If you refer to a particular hardware register from the assembler > code, you probably have to list the register after the third colon > to tell the compiler the register's value is modified." > > My own observation shows that this is true. However, attempting to > add the register in question to the clobber list is returning a > compile error. > > The asm (essentially memset): > > __CRT_INLINE VOID __stosb(PBYTE Dest, BYTE Data, SIZE_T Count) > { > __asm__ > ( > "cld; rep; stosb" > : > : "D" (Dest), "a" (Data), "c" (Count) > : "edi", "memory", "cc" > ); > } > It is probably because the compile finds the input will modify some regs before save its value , in case its value is important for others . try to save original edi on stack ,then use it ,then pop it ,like recovering from an irq. > The error: > > error: can't find a register in class 'DIREG' while reloading 'asm' > error: 'asm' operand has impossible constraints > > Without the edi clobber, this c++ code: > > __stosb((PBYTE)&c, 0, sizeof(c)); > __stosb((PBYTE)&c, 0, sizeof(c)); > > generates this asm: > > 402cd3: cld > 402cd4: rep stos BYTE PTR es:[rdi],al > 402cd6: cld > 402cd7: rep stos BYTE PTR es:[rdi],al > > Since rdi is not clobbered, gcc doesn't reload it between calls > (likewise with rcx). > > While I might be able to fake the compiler out by specifying outputs > (probably need the volatile qualifier too), I don't really want to > change Dest, I just want to use it as an input. > > What's the right way to go here? > > dw

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relationship between cpu_affinity and Packet RX Processing
by Kumar amit mehta March 30, 2013

March 30, 2013

Hi All, I was reading some stuff on interrupts and irq lines today and I thought I'll expermient with the network rx path. To start with, I've a Virtual Machine running 3.8 linux kernel. My machine has 4 CPU cores, network (eth) interface is driven by pcnet_32 AMD driver and is tied to IRQ line #19. I started some network traffic and I notice that out of those 4 CPUs, only one of them is being used and despite changing the CPU affinity, I still don't see the other cores being used for this network traffic. So based on this behavior(please see the logs below), I've these following queries: i) Does it mean that this network card do not have multiple Rx Queues ? ii) I think all the modern NICs must be implementing multiple Rx Queues and hence Can someone please point me to the simplest of such implemenation in any of the in-tree drivers ? iii) I'm just doing a simple 'ping' to google with of big size packets, As I do not have a peer to use packetgen/netperf/iperf utilities. ref: Comments in double quotes. <logs> $ uname -r 3.8.0-rc6-next-20130208 $ cat /proc/cpuinfo |grep processor processor : 0 processor : 1 processor : 2 processor : 3 "Total 4 cpu cores" $ cat /proc/interrupts|egrep 'eth0|CPU' CPU0 CPU1 CPU2 CPU3 19: 5103 74 33 5 IO-APIC-fasteoi eth0 "IRQ Line #19 for the network device" $ lspci|grep -i ethernet 02:01.0 Ethernet controller: Advanced Micro Devices [AMD] 79c970 [PCnet32 LANCE] (rev 10) "AMD NIC" $ lspci -s 02:01.0 -vvv|grep module Kernel modules: pcnet32 $ lsmod|grep pcnet32 pcnet32 40671 0 "driver" # whoami root # cat /proc/irq/19/smp_affinity 03 # cat /proc/irq/19/affinity_hint 00 "I think smp_affinity is a bit map, therefore for all the four cores to be utilized, all 4 bits should be set to 1, which leads to 15(0xf), hence Chaning the cpu affinity" # echo 15 > /proc/irq/19/smp_affinity # cat /proc/irq/19/smp_affinity 15 "started network traffic here and monitoring it" # cat /proc/interrupts|grep eth0 19: 5452 78 33 5 IO-APIC-fasteoi eth0 # cat /proc/interrupts|grep eth0 19: 5488 78 35 5 IO-APIC-fasteoi eth0 # cat /proc/interrupts|grep eth0 19: 5492 78 35 5 IO-APIC-fasteoi eth0 # cat /proc/interrupts|grep eth0 19: 5500 78 35 5 IO-APIC-fasteoi eth0 ................................. .........after some time......... # cat /proc/interrupts|grep eth0 19: 6035 78 42 5 IO-APIC-fasteoi eth0 "Most of the packets are still getting routed through CPU0 *Only*." <logs> -Amit

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How is gpio_keys.ko supposed to work?
by Sven Geggus March 30, 2013

March 30, 2013

Hello, I have a userland application on Raspberry Pi which uses select to read input from a button connected to gpio like this: GPIO --+---- BUTTON ----- GND | +--- RESISTOR 2k -- VCC (3.3V) The sysfs "file" I use select at is /sys/class/gpio/gpioX/value with the method found in Documentation/gpio.txt. However, this same file also states the following: Note that standard kernel drivers exist for common "LEDs and Buttons" GPIO tasks: "leds-gpio" and "gpio_keys", respectively. Use those instead of talking directly to the GPIOs; they integrate with kernel frameworks better than your userspace code could. So how can I make this "standard kernel drivers" work? I would like to get rid of using /sys/class/gpio/gpioX/value and use /dev/input/eventX instead, because the first method will require debouncing in userland and is not portable to other keyboard types. I tried to compile a kernel with CONFIG_KEYBOARD_GPIO enabled and load gpio_keys.ko. However this did neither create a new device in /dev/input/ nor /sys/devices/platform/gpio-keys. Kconfig states the following: ... Your board-specific setup logic must also provide a platform device, with configuration data saying which GPIOs are used. ... So looks like my "board-specific setup logic" (whatever this might be) does not "provide a platform device with configuration data saying which GPIOs are used". So my question is twofold: 1. Where can I find the "board-specific setup logic" (for Rapberry Pi in my case 2. How would this "board-specific setup logic" (if unavailable) look like to make gpio_keys.ko work? Sven P.S.: The kernel in use is the one from git://github.com/raspberrypi/linux.git which is basically a vanilla 3.6.11 with Raspberry Pi specific patches. -- Threading is a performance hack. (The Art of Unix Programming by Eric S. Raymond) /me is giggls@ircnet, http://sven.gegg.us/ on the Web

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