February 2011 - kernelnewbies@kernelnewbies.org

Linux support for Samsung S3C2510A Processor
by Madhavi Manchala Feb. 28, 2011

Feb. 28, 2011

Dear All, Does Linux kernel supports the Samsung S3C2510A processor? Why am I asking this question is, when I looked into the arch/arm/ directory I did not find any thing which is related to Samsung S3C2510A processor. There are other directories like mach-s3c24xx and mach-s3c64xx directories, but not mach-s3c25xx. I checked this in 2.6.37 kernel version which is a stable one. Please sugget me. Thanks and Regards, Madhavi M.

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system call number
by mohit verma Feb. 27, 2011

Feb. 27, 2011

hi all, suppose a process has invoked some system call and cpu runs the system call .how can i find out the system call number (invoked) related to that process in kenrel space? thanks in advance. ........................ *MOHIT VERMA*

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system call number
by mohit verma Feb. 27, 2011

Feb. 27, 2011

hi all, suppose a process has invoked some system call and cpu runs the system call .how can i find out the system call number (invoked) related to that process in kenrel space? thanks in advance. ........................ *MOHIT VERMA*

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Practical character driver
by Sameer Rahmani Feb. 27, 2011

Feb. 27, 2011

hi i write a a character device driver practically, when i load it in kernel, kernel kill the driver because of a crash. i also put the C file in this mail so please review my code please, i want to know problem, mistakes, hints and .... thank you so much here is a tracback ========================= [ 704.202596] Pid: 6912, comm: insmod Not tainted 2.6.37-2 #2 33238RG/33238RG [ 704.202648] RIP: 0010:[<ffffffffa00db0da>] [<ffffffffa00db0da>] module_initial+0xda/0x146 [memchar] [ 704.202722] RSP: 0018:ffff880031c85f08 EFLAGS: 00010246 [ 704.202763] RAX: ffff8801317bf5c0 RBX: 0000000000000000 RCX: 0000000000000000 [ 704.202816] RDX: ffff8801317bf5c0 RSI: ffffffffa00a1320 RDI: 0000000000000008 [ 704.202868] RBP: 0000000000000008 R08: ffff8800bb016350 R09: ffff8800ab0b49c0 [ 704.202921] R10: 0000000000000000 R11: 00000000000136c0 R12: 0000000000000000 [ 704.202974] R13: 0000000000026085 R14: 0000000000040000 R15: 0000000000000003 [ 704.203027] FS: 00007fe95def9700(0000) GS:ffff8800bb000000(0000) knlGS:0000000000000000 [ 704.203087] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 704.203130] CR2: 0000000000000000 CR3: 00000000ab169000 CR4: 00000000000006f0 [ 704.203182] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 704.203240] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 704.203293] Process insmod (pid: 6912, threadinfo ffff880031c84000, task ffff880131741a00) [ 704.203353] Stack: [ 704.203371] 00000000ffffffff 0fc00001810b0439 0000000000000000 0000000000000000 [ 704.203439] ffffffffa00db000 ffffffff8100204a 0000000000026085 ffffffffa00a1400 [ 704.203507] 0000000000026085 0000000000a9c010 0000000000026085 ffffffff810c5b79 [ 704.203574] Call Trace: [ 704.203600] [<ffffffffa00db000>] ? module_initial+0x0/0x146 [memchar] [ 704.203653] [<ffffffff8100204a>] ? do_one_initcall+0x3a/0x180 [ 704.203702] [<ffffffff810c5b79>] ? sys_init_module+0xb9/0x200 [ 704.203749] [<ffffffff81040f52>] ? system_call_fastpath+0x16/0x1b [ 704.203796] Code: 8a 00 00 00 45 31 e4 48 63 0d 2b 63 fc ff 31 c0 48 89 d7 49 8d 6c 24 08 f3 aa 48 c7 c6 20 13 0a a0 48 8b 05 81 65 fc ff 48 89 ef <49> 89 04 24 8b 1d 7c 65 fc ff c1 e3 14 0b 1d ff 62 fc ff e8 8e [ 704.204218] RIP [<ffffffffa00db0da>] module_initial+0xda/0x146 [memchar] [ 704.204275] RSP <ffff880031c85f08> [ 704.204303] CR2: 0000000000000000 [ 704.213239] ---[ end trace 84796bda6e0d2134 ]--- ======================================== /* memchar - Memory map driver Copyright (C) 2011 Sameer Rahmani <lxsameer(a)gnu.org> This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */ #include <linux/init.h> #include <linux/module.h> #include <linux/stat.h> #include <linux/moduleparam.h> #include <linux/fs.h> #include <linux/kdev_t.h> #include <linux/errno.h> #include <linux/slab.h> #include <linux/kernel.h> #include <linux/cdev.h> #include <linux/types.h> #include <linux/fcntl.h> #include <asm/uaccess.h> MODULE_LICENSE("GPL"); MODULE_AUTHOR("Sameer Rahmani <lxsameer(a)gnu.org>"); MODULE_DESCRIPTION("Memory map driver"); struct memmap { char *device; struct cdev cdev; int position; bool eof; }; static int major = 0; static int minor = 1; static int map_size = 100; char *device; module_param(major, int, S_IRUGO); module_param(minor, int, S_IRUGO); module_param(map_size, int, S_IRUGO); static void module_cleanup(void) { dev_t dev; kfree(device); dev = MKDEV(major, minor); unregister_chrdev_region(dev, 1); printk(KERN_ALERT "memchar module un-loaded.\n"); } /* * open function. */ int mem_open(struct inode *inode, struct file *filp) { struct memmap *memory; memory = container_of(inode->i_cdev, struct memmap, cdev); memory->device = device; filp->private_data = memory; /* write-only */ if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) { memory->position = 0; memory->eof = false; } return 0; /* success */ } /* close function */ int mem_release(struct inode *inode, struct file *filp) { return 0; } /* read function */ ssize_t mem_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos) { struct memmap *memory = filp->private_data; ; int counter; if (memory->eof) { return 0; } counter = count; if (count + memory->position > map_size) { counter = map_size - memory->position; } if(copy_to_user(buf, memory->device, counter)) { counter = -EFAULT; return counter; } memory->position += counter; if (memory->position == map_size) memory->eof = true; return counter; } /* write function */ ssize_t mem_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos) { struct memmap *memory = filp->private_data; ; int counter; if (memory->eof) return 0; counter = count; if (count + memory->position > map_size) { counter = map_size - memory->position; } if(copy_from_user(memory->device, buf, counter)) { counter = -EFAULT; return counter; } memory->position += counter; if (memory->position == map_size) memory->eof = true; return counter; } struct file_operations mem_fops = { .owner = THIS_MODULE, .read = mem_read, .write = mem_write, .open = mem_open, .release = mem_release, }; /* * Set up the char_dev structure for this device. */ static void mem_setup_cdev(struct memmap *dev) { int err, devno = MKDEV(major, minor); cdev_init(&dev->cdev, &mem_fops); dev->cdev.owner = THIS_MODULE; dev->cdev.ops = &mem_fops; err = cdev_add (&dev->cdev, devno, 1); /* Fail gracefully if need be */ if (err) printk(KERN_NOTICE "Error %d adding memchar", err); } static int __init module_initial(void) { dev_t dev; int result; struct memmap *memory; if (major) { dev = MKDEV(major, minor); result = register_chrdev_region(dev, 1, "memchar"); } else { result = alloc_chrdev_region(&dev, minor, 1, "memchar"); major = MAJOR(dev); } if (result < 0) { printk (KERN_ALERT "Cannot register major number.\n"); return result; } device = kmalloc(sizeof(char) * map_size, GFP_KERNEL); if (! device) { printk (KERN_ALERT "Allocating device failed.\n"); result = -ENOMEM; goto fail; } memset(device, 0, sizeof(char) * map_size); memory->device = device; mem_setup_cdev(memory); printk(KERN_ALERT "Major: %d", major); return 0; fail: module_cleanup(); return result; } module_init(module_initial); module_exit(module_cleanup); =================================

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messages printed lots of times
by mohit verma Feb. 26, 2011

Feb. 26, 2011

hi all, i am putting a printk() on link_path_walk() kernel function ( the pathname resolution function). i access that printk() only at some special condition (like if pathname passed to link_path_walk() matches with some name) . but when it gets hit like when i pass pathname via unlink(2) , lots of messages are written to dmesg ( or /var/log/messages) . i could not understand why these lots of messages are being written ? (i was hoping for only one message) i check for the match with some perticular filename just for a trial. thanks in advance -- ........................ *MOHIT VERMA*

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from relative to absolute pathname
by mohit verma Feb. 26, 2011

Feb. 26, 2011

hi all, if i call some system call (like open , rename ,unlink, delete and so on) with relative pathname. in kernel space how can i get the full pathname from that relative pathname being passed to that system call ? thanks in advance. -- ........................ *MOHIT VERMA*

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Hello
by Aldyth Maharsha Feb. 26, 2011

Feb. 26, 2011

Hi, i'm new member..i hope can learn about kernel best regards, Aldyth M

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(no subject)
by Aldyth Maharsha Feb. 26, 2011

Feb. 26, 2011

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question about macro __DO_TRACE
by zhao bao Feb. 26, 2011

Feb. 26, 2011

Hello,everybody. When I read tracepoint code, I find variable __data never used. Am I missing something? #define __DO_TRACE(tp, proto, args, cond) \ do { \ struct tracepoint_func *it_func_ptr; \ void *it_func; \ void *__data; \ \ if (!(cond)) \ return; \ rcu_read_lock_sched_notrace(); \ it_func_ptr = rcu_dereference_sched((tp)->funcs); \ if (it_func_ptr) { \ do { \ it_func = (it_func_ptr)->func; \ __data = (it_func_ptr)->data; \ ((void(*)(proto))(it_func))(args); \ } while ((++it_func_ptr)->func); \ } \ rcu_read_unlock_sched_notrace(); \ } while (0)

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Re: syscalls performance
by Enrico Granata Feb. 26, 2011

Feb. 26, 2011

I modified the source code to show exactly how many clock ticks it is taking for each call. It seems that the behavior hinted by Mauro Romano Trajber is actually there: [enrico@espresso ~]$ ./syscallperf 15 4925 1190 942 942 935 942 636 577 627 621 580 591 565 580 565 I am starting to wonder if this depends on the syscall itself OR on some call optimization.. any gcc experts around? Enrico Granata Computer Science & Engineering Department (EBU3B) - Room 3240 office phone 858 534 9914 University of California, San Diego On Feb 25, 2011, at 12:30 PM, Mauro Romano Trajber wrote: > Sure, the code is attached. > > > On Fri, Feb 25, 2011 at 5:15 PM, Daniel Baluta <daniel.baluta(a)gmail.com> wrote: > On Fri, Feb 25, 2011 at 8:22 PM, Mauro Romano Trajber <trajber(a)gmail.com> wrote: > > Thanks Enrico and Daniel, you're right. glibc was caching getpid(); but this > > is not the root cause of this behavior. > > Going further, I decide to use call getpid without glibc, using > > syscall(SYS_getpid) to test this behavior and it happened again. > > Calling it once, the test consumes about 7k CPU cycles and 10 calls consumes > > about 10k CPU cycles. > > Any ideas ? > > Can you post a pointer to your code and information about how you got > this numbers? > > thanks, > Daniel. > > <syscallperf.c>

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