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

About Low Hanging Fruits
by Mayur Patil July 14, 2015

July 14, 2015

Hi, I just want to know like other Open source projects is there a thing in linux kernel as Low hanging fruits. I have searched in bugzilla but not able to find it. Thanks !! -- *Regards,Mayur S Patil,Looking for R&D or Soft Engg positions,Pune, India.*

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Which comments is unnessary?
by Navy July 14, 2015

July 14, 2015

Hi, Here is a code fragment, which comments is unnessary? I think the all the comments should be remove because the comments should show "What to do rather than "How to do?". Am I right? /************************************************************************ * Unit flag definitions for un_flags. ************************************************************************/ #define UN_ISOPEN 0x0001 /* Device is open */ #define UN_CLOSING 0x0002 /* Line is being closed */ #define UN_IMM 0x0004 /* Service immediately */ #define UN_BUSY 0x0008 /* Some work this channel */ #define UN_BREAKI 0x0010 /* Input break received */ #define UN_PWAIT 0x0020 /* Printer waiting for terminal */ #define UN_TIME 0x0040 /* Waiting on time */ #define UN_EMPTY 0x0080 /* Waiting output queue empty */ #define UN_LOW 0x0100 /* Waiting output low water mark*/ #define UN_EXCL_OPEN 0x0200 /* Open for exclusive use */ #define UN_WOPEN 0x0400 /* Device waiting for open */ #define UN_WIOCTL 0x0800 /* Device waiting for open */ #define UN_HANGUP 0x8000 /* Carrier lost */ struct device; /************************************************************************ * Structure for terminal or printer unit. ************************************************************************/ struct un_t { int magic; /* Unit Magic Number. */ struct channel_t *un_ch; ulong un_time; uint un_type; uint un_open_count; /* Counter of opens to port */ struct tty_struct *un_tty;/* Pointer to unit tty structure */ uint un_flags; /* Unit flags */ wait_queue_head_t un_flags_wait; /* Place to sleep to wait on unit */ uint un_dev; /* Minor device number */ struct device *un_sysfs; };

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st_magn_i2c DRDY on INT1 not available error
by Joo Aun Saw July 14, 2015

July 14, 2015

Hi, I have an lsm303dlhc chip with accelerometer and magnetometer sensors. I'm having difficulty getting the st_magn_i2c driver to work. I get this error message: iio iio:device0: DRDY on INT1 not available. st-magn-i2c: probe of 1-001e failed with error -22 This is my device tree fragment: fragment@0 { target = <&i2c_arm>; __overlay__ { #address-cells = <0x1>; #size-cells = <0x0>; status = "okay"; lsm303dlhc-magn@1e { compatible = "st,lsm303dlhc-magn"; reg = <0x1e>; status = "okay"; st,drdy-int-pin = <1>; }; }; }; I'm running kernel 3.18.11. The accelerometer driver works fine though. What am I doing wrong? Any help would be greatly appreciated. Thanks. Joo

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Test
by Navy July 14, 2015

July 14, 2015

I'm a student and it's my first time to use Mailing List. I want to see if somebody can see this mail. Thank you.

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Re: filesystem encryption problem.
by Rohan Puri July 13, 2015

July 13, 2015

On 13 Jul 2015 22:08, "Amir Hezarkhani" <amir6723(a)gmail.com> wrote: > > > On Jul 13, 2015 1:18 AM, "Rohan Puri" <rohan.puri15(a)gmail.com> wrote: > > > > No issues, you are welcome. > > > > Enjoy life, > > Rohan > > > > On 13 Jul 2015 01:19, "Amir Hezarkhani" <amir6723(a)gmail.com> wrote: > >> > >> > >> On Jul 12, 2015 10:00 PM, "Rohan Puri" <rohan.puri15(a)gmail.com> wrote: > >> > > >> > > >> > On 12 Jul 2015 22:20, "Amir Hezarkhani" <amir6723(a)gmail.com> wrote: > >> > > > >> > > Thank for replies. About copy_to_user and copy_from_user, whats the better way? > >> > > I dont have much experience in kernel development but I'm trying to learn. Can you recommend me some books, documents, etc so I can learn more about filesystems in kernel. I am also interested to learn how mmap works because I have problems with execution of binary files in my encrypted filesystem. > >> > > > >> > > On Jul 12, 2015 8:30 PM, <kernelnewbies-request(a)kernelnewbies.org> wrote: > >> > >> > >> > >> > >> > >> > >> > >> On Sun, Jul 12, 2015 at 8:08 PM, Freeman Zhang < freeman.zhang1992(a)gmail.com> wrote: > >> > >>> > >> > >>> -------- Original Message -------- > >> > >>> > hello > >> > >>> > I am working on adding a simple encryption to file contents in ext4 driver > >> > >>> > (for learning purposes) I added simple XOR encryption to aio_read and > >> > >>> > aio_write functions and it worked until I faced this problem: > >> > >>> > > >> > >>> > when I open a file in encrypted filesystem using VIM text editor and when I > >> > >>> > try to save it it gives me this error: > >> > >>> > > >> > >>> >>> pointer block id wrong > >> > >>> >>> can not find line 1 > >> > >>> > > >> > >>> > and it just corrupts the entire file! > >> > >>> > > >> > >>> > this is my aio_write function: > >> > >>> > > >> > >>> > aio_write_enc(struct kiocb *iocb, const struct iovec *iov, > >> > >>> > unsigned long nr_segs, loff_t pos) > >> > >>> > { > >> > >>> > size_t i; > >> > >>> > ssize_t ret; > >> > >>> > char *data=vmalloc(sizeof(char)*iov->iov_len); > >> > >>> > copy_from_user(data,iov->iov_base,iov->iov_len); > >> > >>> > > >> > >>> > for(i=0;i<iov->iov_len;i++) > >> > >>> > { > >> > >>> > data[i]^=5; > >> > >>> > } > >> > >>> > struct iovec iov_enc= { .iov_base = iov->iov_base, .iov_len = > >> > >>> > iov->iov_len }; > >> > >>> > > >> > >>> > copy_to_user(iov_enc.iov_base,data,iov->iov_len); > >> > >>> > ret=ext4_file_write(iocb,&iov_enc,nr_segs,pos); > >> > >>> > vfree(data); > >> > >>> > return ret; > >> > >>> > } > >> > >>> > > >> > >>> > this just changes the data and then calls original function. > >> > >>> > > >> > >>> > is there anything wrong with this function? can anyone help me? > >> > >>> > > >> > >>> > > >> > >>> > > >> > >>> Hi Amir, > >> > >>> > >> > >>> I'm not quite sure about what's wrong with your function, but here are > >> > >>> two suggestions I got from the list when I did similar things: > >> > >>> > >> > >>> 1. wrapfs > >> > >>> 2. ecryptfs > >> > >>> > >> > >>> I think you should check these two stackable filesystems if you haven't. > >> > >>> > >> > >>> Hope this can help a little bit! > >> > >>> > >> > >>> Freeman > >> > >>> > >> > >>> > >> > >>> _______________________________________________ > >> > >>> Kernelnewbies mailing list > >> > >>> Kernelnewbies(a)kernelnewbies.org > >> > >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >> > >>> > >> > >> > >> > >> Hi Amir, > >> > >> > >> > >> I agree with Freeman Zhang over here. The way you are doing it is not right. There is a mechanism to create stacks of file system and you should go down that path. > >> > >> > >> > >> Having said this, you should definitely debug the issue that you are facing. Some pointers : - > >> > >> 1. As you have already mentioned that this is happening only for vim and not while regular read(using cat, etc), you need to check what vim does special to read a file. I would suggest make use of strace and do reading with and without vim, maybe you will get something of interest. > >> > >> 2. re-read code to check, you might be messing up while write or read. > >> > >> > >> > >> Apart from these some basic practices you need to follow is : - > >> > >> > >> > >> 1. check for error conditions, like you missed checking error from vmalloc() and the below code will execute even if it failed, this should be avoided. > >> > >> 2. copy_from_user & again copying back to user is in-efficient. > > Yes you are right. This was the problem. > > >> > >> > >> > >> > >> > >> Enjoy life, > >> > >> Rohan > >> > > > >> > > > >> > > _______________________________________________ > >> > > Kernelnewbies mailing list > >> > > Kernelnewbies(a)kernelnewbies.org > >> > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > >> > > > >> > > >> > Hi Amir, > >> > > >> > Please reply at the bottom. Regarding what's the better way would depend on how you design stuff. > >> > > >> > Following is my recommendation :- > >> > > >> > For conceptual knowledge of general file systems the best would be OS book by Prof Remzi Arpaci-Dusseau. > >> > Excellently explained. > >> > > >> > For linux kernel conceptual stuff get hold of Robert love Linux kernel development. > >> > > >> > Read lots of kernel generic filesystem code in FS dir. Lots of basic functionality is implemented in helper functions present in this dir. > >> > > >> > Enjoy life, > >> > Rohan > >> > >> Thanks a lot Rohan. And sorry about the bad reply. > > Ok I solved the problem. As Rohan said, copy_from_user and then copy_to_user was inefficient. So I removed 'copy to user' part and assigned 'data' to iov_enc.base . thanks guys and Happy codding. Hi Amir, Good to know. Enjoy life, Rohan

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filesystem encryption problem.
by Amir Hezarkhani July 12, 2015

July 12, 2015

hello I am working on adding a simple encryption to file contents in ext4 driver (for learning purposes) I added simple XOR encryption to aio_read and aio_write functions and it worked until I faced this problem: when I open a file in encrypted filesystem using VIM text editor and when I try to save it it gives me this error: >>pointer block id wrong >>can not find line 1 and it just corrupts the entire file! this is my aio_write function: aio_write_enc(struct kiocb *iocb, const struct iovec *iov, unsigned long nr_segs, loff_t pos) { size_t i; ssize_t ret; char *data=vmalloc(sizeof(char)*iov->iov_len); copy_from_user(data,iov->iov_base,iov->iov_len); for(i=0;i<iov->iov_len;i++) { data[i]^=5; } struct iovec iov_enc= { .iov_base = iov->iov_base, .iov_len = iov->iov_len }; copy_to_user(iov_enc.iov_base,data,iov->iov_len); ret=ext4_file_write(iocb,&iov_enc,nr_segs,pos); vfree(data); return ret; } this just changes the data and then calls original function. is there anything wrong with this function? can anyone help me?

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Level irq clear has latency
by buyitian July 12, 2015

July 12, 2015

Hi Experts: My SOC has a RTC module which has a level irq connected to ARM GIC interrupt controller. Once RTC irq is triggered, it will pull high the pin to GIC so that GIC will notify ARM core and at last RTC irq handler will be called, inside handler, I will write a RTC register to clear this irq, RTC HW will pull low the pin to GIC, however, the latency between the writing to RTC register and RTC pull low the pin to GIC is big, let's assume it needs 10ms to complete this, that means I cannot return from RTC irq handler directly because the level irq has not been cleared really, and it needs 10ms to be cleared. I have some choices: 1. Call disable_irq in RTC irq handler, start a timer and then return from irq handler. When timer expires, check RTC irq status again and enable_irq. 2. Pulling RTC irq status register inside RTC irq handler. Which register shall I pull? The GIC irq pending register? Or the RTC module register? 3. Use threaded irq, pulling inside threaded irq handler. Is there any existing code or document or discussion about this irq clear issue? Thanks in advance. Best Regards

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Displaying debug level printk messages in systemd
by Orion Agali July 11, 2015

July 11, 2015

I'm using Arch and I cannot figure out how to get printk debug messages to display in journalctl. I tried the following: * Set LogLevel=debug in /etc/systemd/systemd.conf * Add kernel parameter 'debug' on boot * Setting loglevel=8 in /proc/sys/kernel/printk * dmsg -n 8 Consider the following module: Konsole output ---------- #include <linux/module.h> #include <linux/kernel.h> #include <linux/init.h> static int __init task1_init(void) { pr_notice("I am at level notice"); pr_debug("I am at level debug."); return 0; } static void __exit task1_exit(void){} module_init(task1_init); module_exit(task1_exit); ------------ The notice level is printed but the debug level is not. The debug message is not in dmesg or /dev/kmsg either The answer is probably straight forward, but I've hit a wall so I'm hoping somebody here will be able to point me in the right direction

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I need help understanding how to locate implementation of rdmsr_safe_regs() in the linux kernel
by Marty July 10, 2015

July 10, 2015

I am presently working with Model Specific Registers and have been studying the kernel module implementation found in arch/x86/kernel/msr.c. I am attempting to understand what the implementation of the msr_ioctl(X86_IOC_RDMSR_REGS) <http://lxr.free-electrons.com/source/arch/x86/kernel/msr.c?v=3.8#L124> call is doing. msr_ioctl(X86_IOC_RDMSR_REGS) calls rdmsr_safe_regs_on_cpu() <http://lxr.free-electrons.com/source/arch/x86/lib/msr-smp.c#L242> (arch/x86/lib/msr-smp.c, line 180) which sets up __rdmsr_safe_regs_on_cpu <http://lxr.free-electrons.com/source/arch/x86/lib/msr-smp.c#L228>() (arch/x86/lib/msr-smp.c, line 166) as a callback function to perform the actual work. This callback function then calls rdmsr_safe_regs(). I am unable to find the implementation for rdmsr_safe_regs(). lxr <http://lxr.free-electrons.com/ident?i=rdmsr_safe_regs> only mentions references and a prototype definition. I've also manually grepped through the entire kernel source tree and have not been able to find where rdmsr_safe_regs is defined. I have poked around online, but have so far not been able to generate the correct query to find an answer. Can someone point me to the right documentation where I can figure this out? Thanks, Marty

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what block layer parameter events_dfl_poll_msecs used for?
by yoma sophian July 10, 2015

July 10, 2015

hi all: in block layer, there is one paramter like below: /sys/module/block/parameters/events_dfl_poll_msecs when I search the usage in Document, I cannot find anything. from the src, it seems firing media_chage at a fixed interval. is my guess correct? and is there any furhter debug option I can open to make sure block layer did firing those events to lower device? appreciate your kind help in advance,

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