May 2015 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

A Question Regarding IPV6 Routes in kernel..
by Nagaprabhanjan Bellari May 10, 2015

May 10, 2015

I have observed that for IPv6, whenever we add a subnet, it is associated with the loopback device too which is visible through /proc/net/iv6_route. I don't see this happening with ipv4 routes. Is there any reason for doing so for IPv6 routes? Thanks, -nagp

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Documentation for usbmouse.c
by Ronit Halder May 9, 2015

May 9, 2015

Where do i get documentation for usb mouse ( usbmouse.c ).I was reading /home/roni/linux/drivers/hid/usbhid/usbmouse,c and i am unable to understand some part of it.So,i need help.

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idle task check
by Mustafa Hussain May 9, 2015

May 9, 2015

Hi all, i am working with __sched __schedule() and i want to add some thing i want to check whether the prev will become idle or not how can i do this. thanks in advance - -

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Map syscall nr to syscall name
by sahil aggarwal May 8, 2015

May 8, 2015

Hi all I am looking for an efficient way to convert syscall number to syscall name. I can get syscall number by enabling profiling using perf_event_open(), but cant find way to convert it to actual syscall name. Thanks --sahil

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Re: About head of kernel linked list structure
by Mulyadi Santosa May 8, 2015

May 8, 2015

On Wed, May 6, 2015 at 5:39 PM, Huaicheng Li <lhcwhu(a)gmail.com> wrote: > In my understanding, the head initialised using LIST_HEAD_INIT or defined > by LIST_HEAD corresponds to no *real* data field. > But it *does* have its own _next_ and _prev_ pointers. The _next_ pointer > points to the first real node in the doubly linked list, > and the _prev_ pointer points to the last real node. > > I'm wondering if the picture shown at the very bottom of *http://kernelnewbies.org/FAQ/LinkedLists > <http://kernelnewbies.org/FAQ/LinkedLists>* is wrong about this. Because > I believe head's _prev_ should point to the last node, which is at the > very right. And the last node's _next_ should point to the head. > Just as shown like the red line. > > Am I right? > > > > Hi Huachieng AFAIK, if the linked list is not circular one, the last node's next should point to NULL, so does the head prev's. This is done so you know when you hit head i.e if !(head.prev) { // we're at head } -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

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Appropriate method of io remapping a single memory location?
by maitysanchayan＠gmail.com May 7, 2015

May 7, 2015

Hello, I am adding a small piece of code to expose SoC specific information while following the below information, for a Cortex A5 platform. https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-devices-soc For the SoC device attribute revision, I need to access a location 0x80 for reading the ROM revision information. I am kinda stuck at trying to find the appropriate way to read this location. The devm_ioremap* functions take a device pointer which I can manage but they also need a struct resource argument and devm_ioremap requries a resource_size_t as well. Having only a specific location to read, without having any struct resource what would be the appropriate way to get this information. - Sanchayan.

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reading dynamic array fields in ftrace
by sahil aggarwal May 7, 2015

May 7, 2015

hi, some of the events in ftrace have dynamic array fields. Like : field:__data_loc char[] arg1; offset:24; size:4; signed:1; If i am sampling this particular event using perf_event_open(), how do i read this field i tried: #define get_str(field) (char *)get_dynamic_array(field) #define get_dynamic_array(field) \ ((void *)data + (data->__data_loc_##field & 0xffff)) as done in include/trace/ftrace,h But it gives garble data. TID:28578 PID:28578 TIME:258203626722378 CPU:4 Filename: ^\~@b�^O~H��^H�^? Will appreciate any help. Thanks -sahil

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Preferred userspace IPC mechanism for new drivers?
by Larrew, Jesse May 7, 2015

May 7, 2015

Hello, I’m writing a driver that needs to communicate with userspace applications. Userspace needs to be able to send commands and associated data to the driver, so the ioctl interface seems pretty straightforward. However, LDD3 states that new ioctls in the kernel are a no-no. If that’s the case, then what is the preferred interface to userspace for new drivers? ProcFS seems to be discouraged. Sysfs seems to be more for exporting device model information rather than passing binary blobs back and forth. DebugFS seems to be intended only for debug. Generic Netlink seems like the most viable candidate that I’ve investigated so far. Is that what most people are using these days? Any advice would be greatly appreciated. Thanks! Sincerely, Jesse Larrew Senior Software Engineer AMD Security Architecture R&D jesse.larrew(a)amd.com O: +(1) 512-602-0092 (x50092) M: +(1) 512-791-4852

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About bootmem allocation/freeing flow
by yoma sophian May 5, 2015

May 5, 2015

hi all: I have several questions about free_all_bootmem_core: 1. In __free_pages_bootmem, we set set_page_count(p, 0) while looping nr_pages, why we need to set_page_refcounted(page) before calling __free_pages? 2. how about the pages that allocated by calling alloc_bootmem_xxxx? in free_all_bootmem, we just free the pages that used to record bootmem stage present pages like below. if so, isn't possible the pages got by calling alloc_bootmem_xxxx will be over-written by later page allocation ? page = virt_to_page(bdata->node_bootmem_map); pages = bdata->node_low_pfn - bdata->node_min_pfn; pages = bootmem_bootmap_pages(pages); count += pages; while (pages--) __free_pages_bootmem(page++, 0); appreciate your kind help in advance,

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Calling architecture specific headers files?
by Abhishek Bist May 5, 2015

May 5, 2015

Hi, I am searching the way out that how an architecture specific header's file come into existence.For example the generic defination of spinlock is supposed to call architecture specific spinlock. (linux/spinlock_types.h) typedef struct raw_spinlock { arch_spinlock_t raw_lock; <<<< #ifdef CONFIG_GENERIC_LOCKBREAK unsigned int break_lock; #endif #ifdef CONFIG_DEBUG_SPINLOCK unsigned int magic, owner_cpu; void *owner; #endif #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif } raw_spinlock_t; (x86/include/asm/spinlock_types.h) typedef struct arch_spinlock { union { __ticketpair_t head_tail; struct __raw_tickets { __ticket_t head, tail; } tickets; }; } arch_spinlock_t; what is there which makes to load the architecture specific spinlock (x86) in my case.

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