I need a shared buffer between user and kernel space. I read that one way is to allocated buffer in kernel and then call mmap from the user space. I searched for an example but couldn't find something useful. If you know, could you please send me any links or sample code that does this..
View 1 RepliesLogical Memory Space of 4GB is divided in to 3GB User Space and 1GB Kernel Space. Always. Correct?
1. How can we change it? (just changing value of PAGE_OFFSET is okay?)
2. If system have only 256MB of memory (embedded system) and suppose Kernel Modules eat away all the memory during boot. User space will be left will no memory. Is this case possible?
I am writing device driver in which i have to call callback function from kernel space, which are saving my data. But the callback functions are in userspace. While accessing them i am getting segmentation fault.
View 1 Replies View RelatedI add new syscall, and it need copy big data into the buffer specified in user mode. How can i do it? use copy_to_user? or can i use memcpy directly? If i use copy_to_use, is it low efficient?v
View 2 Replies View RelatedI'm pretty new to this whole (micro)kernel architecture story.
Im wondering if a kernel module is running in kernel or in user space?
Is a driver running as kernel module slower than a driver build into kernel?
If so, are there some current articles, benchmarks?
what difference between user and kernel space.
View 2 Replies View Relatedmeasure kernel space time and user space time?
View 1 Replies View RelatedI am developing a I2C CDROM client driver. The CDROM firmware supports TOC information read through a I2C command. It sends the TOC information in burst ( Interrupts a GPIO pin when it is ready ) and my CPU does a I2C read to read the TOC. When the CDROM firmware finishes sending the last data burst , it informs my CPU that it is done with the TOC, by a flag in the last data burst. I would like to know, which is the most efficinet way I can send these TOC information to userspace?
View 4 Replies View RelatedI wanna write a file in kernel space but from my searching I can to know that instead of writeing file in kernel space ,I can write data to user space by copy_to_user space.
But link is missing ...I dont know how will my user space will access kernel space means my function in kernel space which will do copy_to_user /....How my user space function will call my kernel level function ..
Can any one of you provide me with some example file which are doing this .I know every char driver is using it ...but i could not trace back how user level function is accessing it ...i m confused between user space and kernel space.
How to use execv from kernel space to call a user space program writtenfor socket prog.
I tried to write code for socket in kernel but its not working.
Socket code in kernel is also needed.
I have the following requirement in my module. The driver gets some data from the external device. After getting 1MB of data it has to send it to the user space application. What is the best thing to implement for this in driver.? Is it ok to implement like, after getting data, the driver will send a signal to the user space application. Then the user space application sends an ioctl to read the data. Is there any alternate, that the driver directly sends the data without the user space application asks for it.?
View 4 Replies View RelatedIf the calling process passes me the virtual address of an its array for example, how can I access it without using copy_from_user?
View 2 Replies View RelatedI am writing a program which i dont want the kernel scheduler to preempt before certain time duration. I am using the system call sched_get_priority_max to set the maximum priority. However it is not producing results.
View 3 Replies View RelatedI am using FC10 and recently there has been an error for ssh or telnet "No buffer space available". I rebooted the machine
View 7 Replies View RelatedIn a 32-bit system, max memory addressable is 4GB. Now Linux kernel does memory mapping division of 1GB for kernel address space and 3GB for user address space. That means 4GB of virtual address space is divided between kernel (1GB) and user (3GB).
Q1. All virtual mapping utilizes the available physical RAM without any division? I mean to say that if RAM is 512MB then a page in kernel space can lie any where RAM (leave aside old PCI dma accesses)? (How this fits to fact that kernel memory is non-pageble)
Q2. If a process is created in user space, it has visibility 4GB address space or 3GB address space?
Is it possible for 2 linux machines to mount the same space? The filesystem is Ext3 as mounted by the primary machine. I need to attach a 2nd machine to the same space to see the data for backup purposes. I've tried mounting but I get, "wrong fs type, bad superblock" error.
View 1 Replies View RelatedI have configured pppoe connection via NetworkManager through key-file plugin. The problem is that after a while i cant load any web page. All connections r up, nothing bad in /var/log/messages. Ping produce mystical error message:
Code:
sendmsg: no buffer space available
I'm using OpenVPN 2.1 on Ubuntu 8.10 to connect to LAN behind an IPCOP server. Everything works fine except when I move across the tunnel files which are over 180kb, then I get UDPv4 []: No buffer space available (code=105 surfing the Internet I've found post that suggest to increase these settings on the kernel
> sysctl -w net.core.rmem-max=8388608
> sysctl -w net.core.wmem-max=8388608
> sysctl -w net.core.rmem-default=65536
> sysctl -w net.core.wmem-default=65536
those have actually made a small difference, but not enough for uploading even an image over http. I guess that I can keep increasing those values till I'm not satisfied, but as I'm not sure on what I am dealing with, can anyone tell me if there's a rule of thumb? My machine is a laptop with a dual core processor and 2GB ram.
I am trying to setup 2 individual FTP users. They should both have access to the same directory. They both need to be able to read/write into the directory. But, I want them not to be able to write to each other's files (e.g. delete, remove, rename, etc.).
So let's say the shared directory is: /home/ftp/shared/
UserA needs read/write access to /home/ftp/shared/. UserA should only have write access to his own files. UserB also needs read/write access to /home/ftp/shared/. UserB should only have write access to his own files.
It would be a unix box of sorts, but that is the only restriction. I could use whatever software. I am currently thinking pure-ftpd or vsftp but I am open to all ideas.
I have 2 hdds, with encrypted / and /home. Besides there are four other (encrypted ext4) partitions I use rarely. In Fedora 11 at boottime I gave the luks passphrase for / and home and the system booted as intended.
Whenever I needed those extra encrypted partitions I mounted them in Nautilus. Now, in Fedora 12 at boottime dracut tries to open all the encrypted partitions, / and /home are mounted fine, but opening all the other partitions gave the following messages in messages.log:
Quote:
dracut: luksOpen /dev/sdb6 luks-02a0e706-a26f-4019-a2a0-88a0366a994d
kernel: Buffer I/O error on device dm-0, logical block 124
kernel: device-mapper: ioctl: unable to remove open device temporary-cryptsetup-304
kernel: Buffer I/O error on device dm-0, logical block 124
kernel: Buffer I/O error on device dm-0, logical block 124
[code]....
...and these messages are repeated with the other partiitions, and the boot time takes very, very long. How can I tell dracut to ignore those extra encrypted partitions at boottime?
Is possible to make a folder permission like below?
-User can create files/folders in the shared folder.
-But the files/folders they created, cannot be delete/change by em.
(only can be delete by root users)
-Each new files/folders created will auto owner to root only.
How do you interface with the Linux I2C driver from kernel space? For example, if I had LEDs connected to a GPIO expander on the I2C bus, how would I blink them twice before going down for reset from machine_reset()?
Essentially, I believe I need to call the functions i2c_smbus_write_byte(), i2c_smbus_read_byte(), etc. But these functions require I2C client data that I do not understand how to supply.
I am trying to build linux kernel I am getting out of space after a while. I unpacked it in /usr/src directory. It seems I have plenty of space. How much space does it need to compile & build kernel. I am using VirtualBox.
root@vinay-VirtualBox:/usr/src/linux-2.6.39.3# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 6.9G 3.2G 3.4G 49% /
none 669M 640K 668M 1% /dev
none 675M 24K 675M 1% /dev/shm
none 675M 96K 675M 1% /var/run
none 675M 0 675M 0% /var/lock
/dev/sr0 39M 39M 0 100% /media/VBOXADDITIONS_4.0.10_72479
I hope this is the right place to post to because I haven't found any other related forums.I'm working on an AMD opteron running Linux 2.6.28.6 I want to preload a hardware performance counter (register) with a value to have it overflow after a number of a specific event counts. As I understand, when the counter in the register overflows, an interrupt will be generated and handled by the appropriate interrupt handler. How can my user-level application get notified whenever the interrupt occurs? I want to obtain information on the instruction that caused the overflow. Is this possible? I think this is different than responding to signals with sigaction().
View 1 Replies View RelatedI manage to use the function "time" and "localtime" in gcc.But while I used it in a module in kernel space the above 2 functions are giving error.Even in kernel space time.h header file is not identified. tell the similar time function which can be used in kernel space
View 1 Replies View Relatedcusexmp, the example of CUSE program, works. Is there real programs that makes use of it? For example, a thing that just mirrors other character device or thing that allows networked character devices.
View 1 Replies View RelatedI've been looking to get some torrent downloads running on school servers, but I obviously can't install a torrent client because I don't have root (and by extent, can't run anything requiring root privileges). Servers are running various versions of Red Hat (at least the x86_64 ones are, I don't want to recompile if I don't have to). Google has failed me thus far.
View 13 Replies View RelatedI have written a programme in gcc
#include <time.h>
#include <stdio.h>
int main(void)
[code]...
There are some user-space based NFS clients (e.g. NFS Client library). Can I bypass file permissions by using such client? code...
Client1 uses usual NFS client (kernel-mode based) and user1@client1 can read only file1, but not file2.
As I understand, client1 sends uid in nfs request, server1 do a permissions check based on the request data. So, I suggest this is possible to have a client2:
Client2 uses user-space client, and hacker@client2 knows uids of user1 and user2; If he wants to read file1 he can send uid of user1; if he wants to read file2, he sends uid of user2.
Is the scheme possible?
I am trying to figure out how to mask local timer interrupts on a specific core of a multicore system from within user space. The interrupts are causing latency spikes of 3-10u that we would like to remove. We are only running 1 thread on the core h everything shielded except for these timer interrupts. This thread makes no system calls and thus is never getting context switched out. I am not looking to turn them off entirely but rather turn them off, run my code, turn them on in a continuous loop. The thread runs in user space which we are hoping to maintain. We also have no desire to modify the kernel if possible. I've read about using spinlock_irqsave() but it appears (not positive) that it must be used within kernel space.
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