April 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Re: Cannot get I/O permissions
by Sengottuvelan S April 6, 2011

April 6, 2011

On Fri, Apr 1, 2011 at 3:32 PM, Sengottuvelan S <sengottuvelan.s(a)gmail.com>wrote: > Hi All, > > I am trying to access /dev/mem in my user process. I could not access > because not a privileged access. I tried to use iopl(3) call in linux 2.6, > but i am getting unresolved symbol for this. Is any other way to get access > in user process. I am not sure how to solve this. Can you someone throw some > light on this. > > if(iopl(3)){ > fprintf(stderr, "Cannot get I/O permissions (being root helps)"); > return -1; > } > > if ((fd = open("/dev/mem", O_RDWR | O_SYNC)) < 0) { > fprintf(stderr, "Failed to open /dev/mem"); > return -1; > } > > -- > Regards, > S. Sengottuvelan. > -- Regards, S. Sengottuvelan.

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Problems with yaffs2 and kenrel 2.6.38
by Gasparini Andrea April 5, 2011

April 5, 2011

Hi, has anyone successfully used YAFFS2 with a recent kernel? I'm trying to use it on a Davinci system, the kernel version is 2.6.38-rc8. The effect is that after an reboot (or a unmount/remount) the file written on the filesystem were lost, just like that: root@imega:/mnt# flash_eraseall /dev/mtd3 Erasing 128 Kibyte @ 200000 -- 100 % complete. root@imega:/mnt# mount -t yaffs2 /dev/mtdblock3 target/ yaffs: dev is 32505859 name is "mtdblock3" rw yaffs: passed flags "" root@imega:/mnt# df -h Filesystem Size Used Available Use% Mounted on /dev/mtdblock3 2.0M 768.0K 1.3M 38% /mnt/target root@imega:/mnt# ls -l abigfile -rwxr-xr-x 1 root root 670941 Sep 25 08:26 abigfile root@imega:/mnt# cp abigfile target/ root@imega:/mnt# md5sum abigfile target/abigfile 15a45dba24bbdbb649c523d3b8aabc22 abigfile 15a45dba24bbdbb649c523d3b8aabc22 target/abigfile root@imega:/mnt# touch target/emptyfile root@imega:/mnt# df -h Filesystem Size Used Available Use% Mounted on /dev/mtdblock3 2.0M 1.4M 616.0K 70% /mnt/target After a reboot it behave like that: root@imega:~# mount -t yaffs2 /dev/mtdblock3 /mnt/target/ yaffs: dev is 32505859 name is "mtdblock3" rw yaffs: passed flags "" root@imega:~# ls /mnt/target/ lost+found root@imega:~# df -h /dev/mtdblock3 2.0M 944.0K 1.1M 46% /mnt/target root@imega:~# ls /mnt/target/lost\+found/ obj257 root@imega:/mnt/target/lost+found# ls -l obj257 ---------- 1 root root 670941 Sep 25 08:32 obj257 Someone has ideas on how to debug or can give me some pointer on how to proceed? thanks, bye -- -gaspa-

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kernel API's regarding time conversions
by Mohammed Shafi April 5, 2011

April 5, 2011

Hi all, Is there some kernel API's(like jiffies_to_msecs) already available for any of the following: 1.millisecs_to_seconds 2.seconds_to_minutes 3.minutes_to_hours 4.hours_to_days 5.days_to_months 6.months_to_years sorry if its a basic question. thanks in advance, shafi

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query regarding kernel daemon
by shubham sharma April 5, 2011

April 5, 2011

I was trying some experiments with the kernel daemon. The experiment works as follows: A daemon sleeps in the background. User can enter a string through the proc interface. Whenever a string is entered, the daemon is woke. The daemon keeps a copy of the last entered string in a variable. Initially the variable is initialized to NULL. When the daemon wakes, it checks if the string entered is same as the previous one or a new string is entered. When the string is entered, in case the new or the old strings are NULL, or in case the entered string is same as the old string the daemon goes back to sleep (with the help of the function interruptible_sleep_on(). The problem I am facing is that when I enter the string the second time, the system stalls. I added some sleeps in the code and figured out that when the proc function wakes up the daemon, the system stalls. I have attached the module code with the mail. Any suggestion for the error would be a great help. Shubham

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question regarding down_interruptible
by Vijay Ram Chitrapu April 5, 2011

April 5, 2011

Hi Experts, I have a system in which there is a only 1 user process and a corresponding kernel module (driver) associated with it to send and receive data to the user process. In the kernel module, i have a semaphore to protect a critical section of code during the rx and tx paths. However, at some instance of code execution, the down_interruptible returns EINTR, which means that the user process has received some interrupt due to which the process has come out of sleep due to the signal it received, due to which the kernel module has not got the semaphore. At this point of time, i have no idea as to which signal has triggered the user process to come out of the sleep. Is there a way in which we can know which signal has a process received, without registering any user defined handler to it? Any thoughts/ideas on debugging this problem can be of great help. Also please correct me if i am wrong in any of my understanding regarding down_interruptible. Regards, Vijay

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Re: Regarding enable paging code and swapper_pg_dir.
by James Light April 4, 2011

April 4, 2011

On Sat, Apr 02, 2011 at 01:33:21PM +0530, mindentropy wrote: > On Saturday 02 Apr 2011 2:49:21 am you wrote: > > On Sat, Apr 02, 2011 at 01:37:12AM +0530, mindentropy wrote: > > > Hi All, > > > > > > In the code > > > http://lxr.linux.no/#linux+v2.6.12/arch/i386/kernel/head.S#L186 > > > > > > I am not able to understand what's the reason for subtracting > > > swapper_pg_dir with __PAGE_OFFSET(0xc0000000). i.e. movl > > > $swapper_pg_dir-__PAGE_OFFSET Shouldn't it be movl $swapper_pg_dir, > > > %eax? > > > > > > Thanks. > > > > > > _______________________________________________ > > > Kernelnewbies mailing list > > > > I'm no expert here, but I think the reason that it is coded that way has to > > do with the fact that the swapper_pg_dir is defined to be the value that > > will be used once the CPU has switched to Protected Mode, but this asm > > code in head.S is executing while the processes is in Real Mode. > > > > The instruction that enables paging and protected mode addressing is on > > line 190, I believe. > > > > -James > > Yes but why the subtraction with __PAGE_OFFSET? To put the physical address into cr3 later. $swapper_pg_dir is not the PHYSICAL address of the PGD. So they have to subtract 0xc0000000 (kernel code segment base linear address) from that the get the physical address as the logical address can not be used yet because the paging unit isn't enabled yet. Again, my understanding may be wrong. As I said before, I'm just learning this as well. -James

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Snooping on sockets/file descriptors
by Vimal April 4, 2011

April 4, 2011

Hi, Is it possible for an application (say "snoop", with sufficient privileges) to monitor data on any socket/file descriptor in the system? Here's an example: suppose we have a browser and it creates a tcp socket to connect to a URL. Whenever the browser issues a read() and data is pushed to user space, I want "snoop" to get notified and made available a copy of the same data that the browser read. ptrace can be used to do it, but then there are several ways the app can read data. It could use read(), or recv() or recvmsg(). Is there a better way to deal with this complexity? It's like the action of "tee" on any socket/file descriptor in the system. -- Vimal

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Scheduling policy
by Laurențiu Dascălu April 4, 2011

April 4, 2011

Hello, I'm trying to implement a simple scheduling policy in the Linux kernel, but I'm not sure if I correctly understand the sched_class interface. Specifically, I would like to know more about the following functions: * put_prev_task(struct rq *rq, struct task_struct *prev) Q: It means the prev was preempted and I have to reschedule another task? Or I have just to add prev to the running queue? The code should look something like: if (prev->se.on_rq) { enqueue_task(rq, prev); } or I'm wrong? * task_tick(struct rq *rq, struct task_struct *p, int queued) Q: Should I preempt the task p, by calling resched_task? What does "queued" means? Thanks, -- Laurențiu Dascălu

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Problem in timer interrupt handler with Linux 2.6.27 version
by Asha R April 4, 2011

April 4, 2011

Hi All, I am working on Linux 2.6.27 version. I am facing problem in timer interrupt. I get the timer interrupt but in the handler, evt->event_handler generates prefetch abort. The same code works with Linux 2.6.37 version. Please let me know if anyone has faced this problem before. Regards, Asha

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linux gpio
by Jürgen Lambrecht April 4, 2011

April 4, 2011

Hello, I am new to linux (coming from eCos). My backlight driver does not start up because the reset gpio pin is not correct specified. How does gpio work in Linux? I have 2 platforms that use the same backlight driver, under arm, for freescale imx: imx31_3ds and imx27_3ds. I don't think that matters, I just need to understand the linux gpio. The imx31 platform gives the number 88 as gpio number to the backlight driver. That number comes out of 'iomux-mx3.h'. In 'iomux-mx27.h' the GPIO's are specified in an other way, the "hardware" way, specifying bank and port. I think Linux GPIO needs a sort of general gpio number. But how do I calculate that number out of the datasheet? In the imx31 datasheet, I cannot find that number 88 (or the other numbers in 'iomux-mx3.h'). Kind regards, Jürgen -- Jürgen Lambrecht R&D Associate Tel: +32 (0)51 303045 Fax: +32 (0)51 310670 http://www.televic-rail.com Televic Rail NV - Leo Bekaertlaan 1 - 8870 Izegem - Belgium Company number 0825.539.581 - RPR Kortrijk

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