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How to use pr_debug
by m silverstri Feb. 27, 2014

Feb. 27, 2014

I am using 'pr_debug()' to print debug statements. But I don't see anything in my serial console. But when I use pr_info(), I see the debug statements. Do I need to do anything to see pr_debug()? Thank you.

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Blocked I/O in read() and mmap()
by Le Tan Feb. 26, 2014

Feb. 26, 2014

Hi, I am writing a driver module. Now I have some questions about blocked I/O. my_read() is the read function in the file_operations struct in my module. my_read() is just as simple as this: ssize_t my_read(....) { if(wait_event_interruptible(dev->queue, a == b)) return -ERESTARTSYS; return count; } Then I write a simple program to open and read the device. Obviously the program will be blocked. Now I still can open a new shell window and log in ( I use xshell). However, then I implement my_mmap(), the mmap function in the file_operations struct in my module, like this: int my_mmap(....) { if(wait_event_interruptible(dev->queue, a == b)) return -ERESTARTSYS; return 0; } Then I write a simple program to open and mmap() the device. Obviously the program will be blocked again. However, when I open a new shell window in xshell and try to connect to the linux, it displays like this: Connecting to 192.168.146.118:22... Connection established. To escape to local shell, press 'Ctrl+Alt+]'. And I can't log in! Then after a while, in the syslog, there is one message like this: [38306.614103] INFO: task landscape-sysin:17616 blocked for more than 120 seconds. [38306.614114] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [38306.614120] landscape-sysin D ffffffff8180fb60 0 17616 17609 0x00000000 [38306.614125] ffff88031d609c90 0000000000000082 ffff88032fffdb08 0000000000000000 [38306.614130] ffff8803130bdc40 ffff88031d609fd8 ffff88031d609fd8 ffff88031d609fd8 [38306.614133] ffff88062150c530 ffff8803130bdc40 0000004100000000 ffff8803130bdc40 [38306.614137] Call Trace: [38306.614147] [<ffffffff816b2c49>] schedule+0x29/0x70 [38306.614151] [<ffffffff816b3acd>] rwsem_down_read_failed+0x9d/0xf0 [38306.614157] [<ffffffff81341824>] call_rwsem_down_read_failed+0x14/0x30 [38306.614160] [<ffffffff816b1644>] ? down_read+0x24/0x2b [38306.614166] [<ffffffff81153661>] __access_remote_vm+0x41/0x1f0 [38306.614170] [<ffffffff81153ddb>] access_process_vm+0x5b/0x80 [38306.614175] [<ffffffff811ea423>] proc_pid_cmdline+0x93/0x120 [38306.614178] [<ffffffff811eb425>] proc_info_read+0xa5/0xf0 [38306.614182] [<ffffffff81186e84>] vfs_read+0xb4/0x180 [38306.614185] [<ffffffff81187102>] SyS_read+0x52/0xa0 [38306.614189] [<ffffffff816bc8c2>] system_call_fastpath+0x16/0x1b If I terminate the program by force, then I can log in right now. So, are there any differences between the read and the mmap function to the wait_event_interruptible()? Why? If I want to block mmap() just like blocking read(), what should I do? Or it is impossible? Thanks!

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trying to open a shell on LCD with USB keyboard..
by 김찬 Feb. 26, 2014

Feb. 26, 2014

Hi, folks! Nice to get to know this email list. I hope I finally arrived to the right group. ( I posted my question on stackoverflow 2 weeks ago but there's no reply. I'm analyzing the console-related code, it's too complex..) I'm trying to bring up virtual terminal on our embedded system's LCD usnig USB keyboard which is also connected to the system. I have UART connection to my PC so I've been using UART for console till now but I want to switch to framebuffer console on LCD during the boot at some point.. The USB host controller seems to work fine because I've seen USB memory is attached, read and written ok. And when I connect a keyboard and print the events at keyboard_event function, it prints events that seem normal and corresponding to my action(type of key, press or release..). The problem is that when I configure the framebuffer console in, I cannot see the prints from the busybox code. Maybe our system could have a problem in framebuffer driver (but we can run a application using the framebuffer /dev/fb0) with it not fully supporting framebuffer console. But I have another feeling that it might be just a configuration problem. (So I want to know the right configuration at least to concentrate further..) As you can see, in init/main.c, near the end in init_post function, there is (I'm using linux3.3 by the way) run_init_process(ramdisk_execute_command); (In my case, ramdisk_execute_command = "/sbin/init") And this immediately calls kernel_execve(init_filename, argv_init, envp_init); // above, init_filename and argv_init are "/sbin/init" same. I expect busybox to run after this.. (ramdisk had been installed before by a bootloader-like part) but I cannot see any prints on the LCD after this point. But I can see printks on the LCD until just before calling kernel_execve above. I'm using linux 3.3. I understand I have to open a frame buffer console on LCD and connect it to a tty but I don't know how. Below are printed the current releavant settings. (In serial UART connection case, linux boots ok up to the final busybox shell prompt printing things in busybox initialization after kernel_execve call. and #cat /proc/fb0 returns 0 for your info. Only LCD/framebuffer console mode stops after kernel_execve.) in kernel source directory, #### arch/sparc/boot/ourprocessor/prom_stage.c : ##### // "console=ttyS,mmio,0xff003000,115200n8 " <== serial port case "console=tty0 " <= frame buffer console case (below line too) "fbcon=font:SUN8x16,map:0 " <= Is this boot argment correct?.. in ramdisk image, #### /sbin/init: ##### #!/bin/busybox sh export LD_LIBRARY_PATH=/lib export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/mnt/nand/lib exec /bin/busybox init ### /etc/init.d/rcS ##### mknod /dev/tty0 c 4 0 <== Do I need to explicitly make tty0 and tty1 like this? mknod /dev/tty1 c 4 1 mknod /dev/tty2 c 4 2 mknod /dev/tty3 c 4 3 mknod /dev/tty4 c 4 4 ### .config ##### CONFIG_FRAMEBUFFER_CONSOLE=y <= LCD/framebuffer console case. Otherwise none. CONFIG_FONT_SUN8x16=y CONFIG_LOGO=y By the way, I'm not using /etc/inittab.(so use default init). The busybox init/init.c code says if there isn't the inittab file and console is not the serial port, it runs tty2::askfirst:/bin/sh tty3::askfirst:/bin/sh tty4::askfirst:/bin/sh (starting shell on tty 2, 3 and 4) then How do make tty2's shell appear on the LCD/framebuffer/framebuffer console? It's confusing and books are not so kind.. Any hint would be deeply appreciated. Thank you in advance. Chan

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query on VFS busy inode
by Abhishek Dave Feb. 26, 2014

Feb. 26, 2014

Hello All, Can some one please help me to understand meaning of below code <snip> if (!list_empty <http://lxr.free-electrons.com/ident?i=list_empty>(&sb <http://lxr.free-electrons.com/ident?i=sb>->s_inodes)) {406 <http://lxr.free-electrons.com/source/fs/super.c#L406> printk <http://lxr.free-electrons.com/ident?i=printk>(*"VFS: Busy inodes after unmount of %s. "*407 <http://lxr.free-electrons.com/source/fs/super.c#L407> *"Self-destruct in 5 seconds. Have a nice day...\n"*,408 <http://lxr.free-electrons.com/source/fs/super.c#L408> sb <http://lxr.free-electrons.com/ident?i=sb>->s_id);409 <http://lxr.free-electrons.com/source/fs/super.c#L409> } </snip> Are we doing here? Thanks, Dave

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Re: Google Summer of Code 2014 - IPP-over-USB printer support - Joint project idea for OpenPrinting and the kernel
by Till Kamppeter Feb. 25, 2014

Feb. 25, 2014

On 02/25/2014 06:20 PM, Linus Torvalds wrote: > On Tue, Feb 25, 2014 at 9:01 AM, Till Kamppeter > <till.kamppeter(a)gmail.com> wrote: >> >> First, I want to make a feature request to the kernel to add it. Second, >> I want to suggest this as a Google Summer of Code project, asking for >> mentors on the kernel side. Mentoring Organization will be the Linux >> Foundation, hosting projects for both OpenPrinting and the kernel. > > It certainly sounds like a worthy thing, but wasn't the deadline for > GSoC last Friday? I know both Subsurface and X.org did that, and got > accepted early this week. No, the deadline was only for mentoring org applications (and as mentoring org we, the LF, are accepted). Project ideas can be added until the student application deadline, only the earlier they get posted, the more potential student candidates will read them and consider them for their applications. In addition, project ideas get posted on the project's sites, not at Google. Also they can get posted at more than one place. So we should determine ASAP who could mentor this project and post the project on our idea lists. Till

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Re: [kernel]which the file define the variable of "phys_base"?
by Sunny Feb. 25, 2014

Feb. 25, 2014

It didn’t show me anything like that. It worked well. Here is what I have - note that I changed couple of things in printk statement but that shouldn’t affect your errors: __________________________________________________ Program - lx.c #include <linux/module.h> // for printk() #include <linux/mm.h> // for struct page #include <asm/page.h> // for struct page #include <asm/pgtable.h> // for ZERO_PAGE static int __init init_hello( void ) { int i; struct page * zero_page; printk(KERN_ALERT "\n Kello, the first! \n\n" ); i = 0x100; zero_page = ZERO_PAGE(&i); printk(KERN_ALERT " the ZERO address is %p", zero_page); return 0; } static void __exit exit_hello( void ) { printk(KERN_ALERT "\n Goodbye now... \n\n" ); } MODULE_LICENSE("GPL"); module_init(init_hello); module_exit(exit_hello); Makefile obj-m :=lx.o KDIR= /lib/modules/$(shell uname -r)/build all: $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules clean: rm -rf $(wildcard *.o *.ko mo* Mo* *.mod.c) ____________________________________________________ Running make gives me(I’m in a Virtual Machine so the page addresses may be messed up): sunny@ubuntu: make make -C /lib/modules/3.11.0-12-generic/build SUBDIRS=/home/sunny/Documents/ modules make[1]: Entering directory `/usr/src/linux-headers-3.11.0-12-generic' Building modules, stage 2. MODPOST 1 modules make[1]: Leaving directory `/usr/src/linux-headers-3.11.0-12-generic' sunny@ubuntu: sudo insmod lx.ko sunny@ubuntu: sudo rmmod lx sunny@ubuntu: sudo dmesg | tail -6 [48391.359434] Kello, the first! [48391.359434] [48320.368773] the ZERO address is ffffea0000079b40 [48391.359439] the ZERO address is ffffea0000079b40<1>[48411.409906] [48411.409906] Goodbye now... [48411.409906] Hope this helps! Don’t forget to ‘reply all’ so that others in the mailing list could also see your/my problem/solution. - Sunny On Feb 24, 2014, at 7:32 PM, lx <lxlenovostar(a)gmail.com> wrote: > hi : > If i command the "insmod zero.ko"; the wrong messages is: > ############## > insmod: error inserting 'zero.ko': -1 Unknown symbol in module > ############## > > > 2014-02-25 2:33 GMT+08:00 Sunny <sundarcs(a)gwu.edu>: > Hi, > > I’m not sure about the “pays_base” warning, but your code runs fine in my machine. What happens if you ignore the warning and load the module anyway? > > - Sunny > > On Feb 24, 2014, at 9:04 AM, lx <lxlenovostar(a)gmail.com> wrote: > >> hi all: >> the codes is: >> ######################################### >> #include <linux/module.h> // for printk() >> #include <linux/mm.h> // for struct page >> #include <asm/page.h> // for struct page >> #include <asm/pgtable.h> // for ZERO_PAGE >> >> static int __init init_hello( void ) >> { >> int i; >> struct page * zero_page; >> printk( "\n Kello, the first! \n\n" ); >> i = 0x100; >> zero_page = ZERO_PAGE(&i); >> printk(" the ZERO address is %p", zero_page); >> return 0; >> } >> >> static void __exit exit_hello( void ) >> { >> printk( "\n Goodbye now... \n\n" ); >> } >> >> MODULE_LICENSE("GPL"); >> module_init(init_hello); >> module_exit(exit_hello); >> ######################################### >> >> I complier it. by: >> ######################################### >> make -C /lib/modules/`uname -r`/build M=`pwd` >> ######################################### >> >> the results is: >> ######################################### >> [root@localhost kernel_test]# make -C /lib/modules/`uname -r`/build M=`pwd` >> make: Entering directory `/usr/src/kernels/2.6.18-308.el5-x86_64' >> CC [M] /opt/lx/kernel/kernel_test/zero.o >> Building modules, stage 2. >> MODPOST >> WARNING: "phys_base" [/opt/lx/kernel/kernel_test/zero.ko] undefined! >> LD [M] /opt/lx/kernel/kernel_test/zero.ko >> make: Leaving directory `/usr/src/kernels/2.6.18-308.el5-x86_64' >> ######################################### >> >> I try to find the file which defined the "phys_base", for examples; >> phys_base >> >> Defined as a variable in: >> arch/sparc/mm/init.c, line 40 >> arch/sparc64/kernel/sparc64_ksyms.c, line 110 >> arch/sparc64/mm/init.c, line 47 >> include/asm-sparc/page.h, line 160 >> include/asm-sparc/pgtable.h, line 122 >> include/asm-sparc64/pgtable.h, line 227 >> >> But I can't find the file of init.c in my computer. Please tell me some ways to solve it, thank you. >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >

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Need help regarding Mailing list
by Kalyan Kodamagula Feb. 25, 2014

Feb. 25, 2014

I had subscribed to the mailing list of the below : kernel code for beg's and linux sub-system /drivers. I got mails from the subscribed ML.I was wondering ppl all are asking douts or suggestion via mails and i cannot see any threads for the same mail.It was quiet confusing for me where the thread starts and ends. Is there any links like : http://forum.kernelnewbies.org/ ? if yes please point it. where we can see replies on the same thread. Please suggest me if anything wrong im doing. Thanks.

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Kernel Development
by subham soni Feb. 25, 2014

Feb. 25, 2014

Hello, I am a newbie to kernel development. I would like to develop my own kernel from scratch. From where should I start from? I have a good experience of the commands in Linux (Ubuntu,Fedora,Debian,Slackware). I googled out and I came to know that I should start from Device Drivers. Now which device driver should I code? Or should I master Shell Scripting? For developing a kernel (my aim here would be to increase the battery life, since most laptops have only 1.30 hrs or 2.00 hrs in Linux OS) and 3.00 hrs in Windows Environment. How should I start and from where?

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Questions about slab and mmap
by Le Tan Feb. 25, 2014

Feb. 25, 2014

Hello, I am writing a driver module and doing something with slab and mmap. Now I have some problems and need help. 1. I use kmem_cache_create() to create my own slab cache. It returns success. But I can't find my slab item in /proc/slabinfo. Why? 2.If I want the object in the slab cache to be page-aligned, what should I do? Because I want to alloc a memory of size 4096B, and want the memory to be in one page. 3. My driver module maps pages, allocating by kmem_cache_alloc(), to userspace through mmap(). In the userspace program, I first mmap() my driver device, then read something from the address returned, then munmap() it. Sometimes after the program calls munmap(), some error messages will be printed to the log: [42522.596729] BUG: Bad page map in process logger_pro pte:8000000612a30025 pmd:314175067 What will be possible reasons? Now I will explain my problems in detail. My module is called "logger". Logger maintains a list of pages (each of them is 4096B). Kernel will put some data into logger. Logger put them in the list of pages in order. When a page is full, logger will alloc another page, and then fill it with data. For efficiency, I use slab. data_cache = kmem_cache_create("logger_data", 4096, 0, 0, NULL); //I use this to create my own cache. This is called in the init function of my module kmem_cache_alloc(data_cache, GFP_ATOMIC); // I use this to alloc a new page, use GFP_ATOMIC to avoid sleep. It is called in another place Then I insmod logger. There is no error message. And my driver seems to work. However, I can't find the corresponding item in /proc/slabinfo. Why? I then write a userspace program called "logger_pro" to read data from logger into a file. For efficiency, I ues mmap() to map one page at a time, then read the data to the file.It is as follows: while(1) { str = mmap(vma); //always map the same address and offset (they are set to zero), logger will handle this fwrite(str, 4096, fd); munmap(str); } In logger module, the logger_vma_fault() function will always returns the first page in the list. When logger_pro munmap(), logger's function logger_vma_close() will be called. In logger_vma_close(), logger delete the page that has been mapped just now using kmem_cache_free(). So, though logger_pro always mmap() the same address and logger always return the fisrt page, logger_pro will eventually read all the data out of logger and logger will delete all the pages that have been read. Everything seems to be OK. But sometimes there are errors in the log: [42522.596689] logger_mmap():start:7f8ff57be000, end:7f8ff57bf000 //this is the mmap() function of my device module [42522.596694] logger_vma_fault():vmf->pgoff:0d,start:7f8ff57be000,pgoff:0,offset:0 //this is the fault function of struct vm_operations_struct [42522.596729] BUG: Bad page map in process logger_pro pte:8000000612a30025 pmd:314175067 //this is the error [42522.596740] page:ffffea00184a8c00 count:2 mapcount:-2146959356 mapping: (null) index:0xffff880612a36000 [42522.596747] page flags: 0x200000000004080(slab|head) [42522.596811] addr:00007f8ff57be000 vm_flags:04040071 anon_vma: (null) mapping:ffff880613b25f08 index:0 [42522.596824] vma->vm_ops->fault: logger_vma_fault+0x0/0x140 [logger] [42522.596834] vma->vm_file->f_op->mmap: logger_mmap+0x0/0xd50 [logger] [42522.596842] CPU: 1 PID: 21571 Comm: logger_pro Tainted: G B IO 3.11.0+ #1 [42522.596844] Hardware name: Dell Inc. PowerEdge M610/000HYJ, BIOS 2.0.13 04/06/2010 [42522.596846] 00007f8ff57be000 ffff880314199c98 ffffffff816ad166 0000000000006959 [42522.596851] ffff880314539a98 ffff880314199ce8 ffffffff8114e270 ffffea00184a8c00 [42522.596854] 0000000000000000 ffff880314199cc8 00007f8ff57be000 ffff880314199e18 [42522.596858] Call Trace: [42522.596867] [<ffffffff816ad166>] dump_stack+0x46/0x58 [42522.596872] [<ffffffff8114e270>] print_bad_pte+0x190/0x250 [42522.596877] [<ffffffff8115027b>] unmap_single_vma+0x6cb/0x7a0 [42522.596880] [<ffffffff81150bd4>] unmap_vmas+0x54/0xa0 [42522.596885] [<ffffffff81155aa7>] unmap_region+0xa7/0x110 [42522.596888] [<ffffffff81157f97>] do_munmap+0x1f7/0x3e0 [42522.596891] [<ffffffff811581ce>] vm_munmap+0x4e/0x70 [42522.596904] [<ffffffff811591bb>] SyS_munmap+0x2b/0x40 [42522.596915] [<ffffffff816bc9c2>] system_call_fastpath+0x16/0x1b [42522.596920] logger_vma_close():start:7f8ff57be000, end:7f8ff57bf000, vmas:0 //this is the close function of struct vm_operations_struct So what is wrong here? Any suggestions? Thanks! I am sorry that this email is a little messy.

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Object file section efficiency
by Matt Davis Feb. 24, 2014

Feb. 24, 2014

Hello, Suppose I have some initialized data stored in the .data section of my kernel module. Now, as it turns out, that data should have been made constant, but the latter 'const' linkage qualifer was left off of the declaration of the variable. This led me to the following question: Are there any memory efficiencies with how the kernel loads the .data vs the .rodata sections into memory? Will the information stored in .rodata have better cache performance than that stored in .data? -Matt

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