- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Simple Read operation on a misc device driver
by Aldo Esteban Paz April 19, 2014

April 19, 2014

For the Eudyptula's Chanllenge Task 6, i need to write a misc device driver with simple read/write operations. The following was the answer to part of my code: > static char eid[] = EUDYPTULAID; > > static ssize_t misc_device_read(struct file *file, char __user *buf, > size_t count, loff_t *ppos) > { > if (*ppos == sizeof(eid)) > return 0; > else > if (*ppos != 0 || count < sizeof(eid)) > return -EINVAL; > > if (copy_to_user(buf, eid, sizeof(eid))) > return -EINVAL; > > *ppos = sizeof(eid); > > return *ppos; > } This whole function can be made much more "simple" and reduced to one single line {hint} (It's just a "simple" function call {hint}). Anyone know that "single" function?

4 3

[RFC] Only a.out QMAGIC format is working
by Geyslan Gregório Bem April 19, 2014

April 19, 2014

Sirs, I was researching about old binary formats and did some tests. Meantime, I was able to run sucessfully only the QMAGIC format. Nonetheless, the OMAGIC, NMAGIC and ZMAGIC didn't work anymore. The test occurred using old slackware binaries and some new, the latter compiled by me, using cross-compiled as and ld. In any case, the QMAGIC was the only functional. After some debugging I identified (when loading a OMAGIC) that the kernel sigkill the current after this checking: http://lxr.linux.no/linux+v3.13.5/arch/x86/ia32/ia32_aout.c#L325 325 error = vm_brk(text_addr & PAGE_MASK, map_size); 326 327 if (error != (text_addr & PAGE_MASK)) { 328 send_sig(SIGKILL, current, 0); 329 return error; 330 } I suppose this happens due to changes made, in the course of time, in the memory mapping (vm_brk/do_brk), therefore the only one that still works is the QMAGIC (the aligned one). Or maybe, it's purposely. [RFC] Is important to note that when a ZMAGIC is loaded what happens is a "Segmentation fault" and not "SIGKILL". That was reported by others too: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/966472 -- Regards, Geyslan G. Bem hackingbits.com

2 1

Re: System load notification
by Jimmy Thrasibule April 17, 2014

April 17, 2014

> 'batch' is supposed to do this, though I haven't used it. What do you mean by "batch"? __ Jimmy

2 2

System load notification
by Jimmy Thrasibule April 17, 2014

April 17, 2014

Hi, Let's say I have a resource intensive process that I would like to be ran only when the system is doing nothing and since another process is starting to drain resources from the system, stop the first one. So I wonder if we can ask the kernel to send a signal to reproduce this behavior? The way I see it is to write a daemon subscribing to receive a signal when the system is idle (or low on load) for a certain amount of time, and to receive another signal when the system starts to be high loaded. Of course the load produced by the process itself should be excluded. Any idea? -- Jimmy

1 0

loglevel 7 (debug) and pr_debug()
by Martin Kepplinger April 16, 2014

April 16, 2014

I'm on Debian here and I don't really get pr_debug and printk(KERN_DEBUG ...). Let's stick to pr_debug. I have DYNAMIC_DEBUG enabled and root@laptop:/proc/sys/kernel# cat /proc/sys/kernel/printk 7 7 1 7 I write a module with pr_debug's. I load the module and I *don't* see anything in /var/log/messages (or anywhere in /var/log/* ). Adding #define DEBUG doesn't help. /sys/kernel/debug/dynamic_debug/control has the pr_debug entries I use in my loaded module. In short: How do I see debug log messages? Using pr_info() works as expected. What am I missing? Do I need to edit my Makefile? thanks! martin -- Martin Kepplinger e-mail martink AT posteo DOT at chat (XMPP) martink AT jabber DOT at

4 9

Contributing to the device driver staging section of the linux tree
by Kashyap Gada April 15, 2014

April 15, 2014

Hello, I want to re start the code clean up stuff in the staging branch of drivers in the linux tree. I have done this before some time back on the 2.6 branch. I want to get back to atleast start off again (I am learning developing device drivers) to be active in the community. My question is that the latest linux kernel is 3.x there have been so many versions of it since 2.6. So how to decide which branch we should be working on and which is relevant enought in todays time. Thanks Kashyap Gada gada.kashyap(a)gmail.com

2 1

Questions regarding del_timer_sync() and re-registering timers
by Jimmie Mayfield April 15, 2014

April 15, 2014

Hi. The conventional wisdom when mixing del_timer_sync() with timers that re-register themselves is that the caller must ensure that re-registration does not happen. >From kernel/timer.c: * Synchronization rules: Callers must prevent restarting of the timer, * otherwise this function is meaningless. Now, the pseudo-code for del_timer_sync and try_to_del_timer_sync looks something like this (ignoring the lock manipulation): while (1) { if (timer is not running) { if timer is pending then detach it break } else { sleep } } So that the loop continues to spin until the timer function is no longer running at which point the kernel checks the pending list and removes it if necessary. Q: So given this construct, why is it imperative that the timer function not re-register itself? I could understand that restriction if the timer function might be running on another CPU when the "if timer is pending then detach" step is executed but it's not obvious to me how that's possible since base->lock is owned at that point (not shown in the pseudocode)? Can someone briefly point out what I've missed? Jimmie

1 0

about BTFIXUPSET_.. macros (for sparc, MMU)
by 김찬 April 15, 2014

April 15, 2014

Hi, in the linux initialization, inside setup_arch, I see ld_mmu_srmmu() (I'm working on SPARC architecture, SRMMU is Sparc Reference MMU) and it comprises many macro calls starting with BTFIXUP... The first two lines look like this BTFIXUPSET_SIMM13(pgdir_shift, SRMMU_PGDIR_SHIFT); // ___ss_pgdir_shift <-- "first line" BTFIXUPSET_SETHI(pgdir_size, SRMMU_PGDIR_SIZE); // ___hs_pgdir_size ... The macro in the first line BTFIXUPSET_SIMM13 is expanded to #define BTFIXUPSET_SIMM13(__name, __val do { ___ss_##__name[0] |= 1; ___ss_##__name[1] = (unsigned)__val; } while (0) So the first line just becomes ___ss_pgdir_shift[0] |= 1; ___ss_pgdir_shift[1] = (unsigned)SRMMU_PGDIR_SHIFT; I looked up __ss_pgdir_shift, and found it's in arch/sparc/boot/btfix.S, ___ss_pgdir_shift: .word 0x73000000,0,68 .word _stext+0x000148c8,0,_stext+0x00014c94,0,_stext+0x00015348,0,_stext+0x00016310,0,_stext+0x000163c8,0,_stext+0x00016fb4,0,_stext+0x00017508,0,_stext+0x0007c31c,0,_stext+0x0007c9b0,0,_stext+0x0007da94,0,_stext+0x0007e310,0,_stext+0x0007edbc,0,_stext+0x0007f058,0,_stext+0x0007f234,0,_stext+0x0007f950,0,_stext+0x0007fbb4,0,_stext+0x00080408,0,_stext+0x00084540,0,_stext+0x00084c30,0,_stext+0x00085a60,0,_stext+0x00086598,0,_stext+0x00087b40,0,_stext+0x00087ce4,0,_stext+0x00088c54,0,_stext+0x00089f58,0,_stext+0x0008d748,0,_stext+0x003d08f4,0,__init_begin+0x0000659c,0,__init_begin+0x00007ac8,0,__init_begin+0x00008088,0,__init_begin+0x00008360,0,__init_begin+0x00008720,0,__init_begin+0x00008908,0,__init_begin+0x00008bf8,0 I think this assembly code was built before the compilation of ld_mmu_srmmu. (this BTFIXUP thing sounds like related to what is called pre-link, I saw it on the web) and This ld_mmu_srmmu function seems to setup general sparc functions and values into those for specific sparc sub-architectures. (replacing genearal things with more specific things) So the first line is setting bit 0 of 0x73000000 and overwriting SRMMU_PGIDR_SHIFT (=2^24) at the next word. and there is a number 68 and it is followed by 68 words. I can see it looks like setting up a page directory table with certain length. But how has this assembly been built during pre-link? Is there any good reference I can read? And Where and how are this values and functions used? Could somebody give me any answer? Sorry for many hasty questions. Best regards, Chan

1 0

about BTFIXUPSET_.. macros..
by Chan Kim April 15, 2014

April 15, 2014

Hi, in the linux initialization, inside setup_arch, I see ld_mmu_srmmu() (I'm working on SPARC architecture, SRMMU is Sparc Reference MMU) and it comprises many macro calls starting with BTFIXUP... The first two lines look like this. BTFIXUPSET_SIMM13(pgdir_shift, SRMMU_PGDIR_SHIFT); // ___ss_pgdir_shift <-- "first line" BTFIXUPSET_SETHI(pgdir_size, SRMMU_PGDIR_SIZE); // ___hs_pgdir_size ... The macro in the first line BTFIXUPSET_SIMM13 is expanded to #define BTFIXUPSET_SIMM13(__name, __val) \ do { \ ___ss_##__name[0] |= 1; \ ___ss_##__name[1] = (unsigned)__val; \ } while (0) So the first line just becomes ___ss_pgdir_shift[0] |= 1; ___ss_pgdir_shift[1] = (unsigned)SRMMU_PGDIR_SHIFT; If I look up __ss_pgdir_shift, it is found in arch/sparc/boot/btfix.S, ___ss_pgdir_shift: .word 0x73000000,0,68 .word _stext+0x000148c8,0,_stext+0x00014c94,0,_stext+0x00015348,0,_stext+0x00016310,0,_stext+0x000163c8,0,_stext+0x00016fb4,0,_stext+0x00017508,0,_stext+0x0007c31c,0,_stext+0x0007c9b0,0,_stext+0x0007da94,0,_stext+0x0007e310,0,_stext+0x0007edbc,0,_stext+0x0007f058,0,_stext+0x0007f234,0,_stext+0x0007f950,0,_stext+0x0007fbb4,0,_stext+0x00080408,0,_stext+0x00084540,0,_stext+0x00084c30,0,_stext+0x00085a60,0,_stext+0x00086598,0,_stext+0x00087b40,0,_stext+0x00087ce4,0,_stext+0x00088c54,0,_stext+0x00089f58,0,_stext+0x0008d748,0,_stext+0x003d08f4,0,__init_begin+0x0000659c,0,__init_begin+0x00007ac8,0,__init_begin+0x00008088,0,__init_begin+0x00008360,0,__init_begin+0x00008720,0,__init_begin+0x00008908,0,__init_begin+0x00008bf8,0 I think this assembly code was built before the compilation of ld_mmu_srmmu. (this BTFIXUP thing sounds like related to what is called pre-link, I saw it on the web) and This ld_mmu_srmmu function seems like to setup functions and values into specific sparc sub-architectures. (replacing genearal things with more specific things) So the first line is setting bit 0 of 0x73000000 and writing SRMMU_PGIDR_SHIFT (=2^24) to the next word. and there is a number 68 and it is followed by 68 words. I can see it looks like setting up a page directory table with certain length. But how has this assembly been built during pre-link? Is there any good reference? How are this values and functions used? I mean in what manner? Could somebody give me and idea how it's used later? Sorry for hasty questions. Best regards, Chan

1 0

Linux on PS4?
by Peter Senna Tschudin April 14, 2014

April 14, 2014

Did anyone succeed to run Linux on a Playstation 4? If so can one share instructions with me? Do one want help for making it happen? I would love to have a PS4 as a high end, compact, and cheap workstation for compiling Kernels... -- Peter

1 0