General :: Virtual Space Seen By Each New Process In User Space?
Jun 21, 2010
In 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?
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Jan 4, 2010
Logical 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?
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Jun 29, 2010
For the past few days I was putting effort on understanding the software control flow starting from "Boot loader" to "Linux User space".
I am consolidating the entire process and putting forth in this forum...It would be great if someone can validate this..It might be useful to other new bees too.
Step 1 : Power up the board
Step 2 : The CPU control goes to EEPROM/storage memory where BIOS resides
Step 3: BIOS gets loaded in RAM and gets executed
Step 4: During execution, the selection of Boot device has to be done with the help of BIOS Menu [Blue screen appearance during start up in normal PC's]
Step 5: BIOS shall access the Bootloader stored in boot device [for eg.,Hard disk]. Boot loader is stored in MBR area.
for explanation purpose I take the following configurations
Bootloader = GRUB
Boot Device = Hard Disk
Step 6: GRUB shall be loaded in RAM and gets executed
Step 7: GRUB shall load the KERNEL image to RAM. Kernel image is stored in Hard Disk.
The question of "How the GRUB knows where the Kernel image is stored".
The answer is
1. In the "Grub.config" file, the location of "Kernel Image" and " Ramdisk Image" [which will be discussed later in the section] is being given.
Step 8: Kernel Image followed by Ramdisk Image is loaded in RAM by GRUB bootloader
Step 9: Kernel Image gets executed...During execution, top portion of the code shall make initial hardware initialization and latter part
of the code shall just decompress the Kernel Image
Step 10 : After decompressing the Kernel Image, it shall decompress
the already loaded Ramdisk Image
Ram disk is just creating a temporary hard disk in RAM. The main responsibility includes it consists of minimal driver files, executables, directory structures to created a TEMPORARY ROOT FILE SYSTEM.
This Temporary Root File system shall be used by Kernel Image
1. Execute the executables to access the Hard disk
2. For creating Permanent Root File System in HARD DISK
Step 11 : Kernel Shall look for the file /Linuxrc in Ramdisk. Linuxrc
is a USER script file [not sure]
Step 12: At the end of script file Linuxrc, the Ramdisk shall give the
control to "USER SPACE" [path for writing the script not known]in Linux kernel
Step 13: USER SPACE is the normal shell
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Sep 22, 2009
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.
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Dec 13, 2010
I 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?
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Jul 7, 2009
I 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.
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Jul 14, 2009
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.
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Dec 10, 2008
I 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.
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Jul 21, 2011
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.?
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Nov 28, 2010
measure kernel space time and user space time?
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Oct 14, 2009
I have a list of files in a directory which starts with - or have space.
I need to copy them back without the space or -?
linux1[sim]% ls linux1[sim]% cp ./-* ./*
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Feb 17, 2011
Suppose a process creates multiple shared mem segments as part of it job.Now is it always possible that on restart, that process can reattach to those previously created shared mem segments to the same virtual address spaces (returned on first time creation) ? My intention is use pointers over shared memory.So on restart I want those pointers absolute value to remain valid.
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Apr 21, 2010
I have millions of small chunks of new's and delete's in my program. Even though no memory leak is detected through valgrind or purify, memory grows. But the growth is degrading over the number of times of the execution of the tasks. Can i think that fragmentation plays a role in this?
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Jul 5, 2011
My system is dual boot with win7 and ubuntu. I have free space of around 10 gb. I want to add this free space to my ubuntu drive. How can i do that?
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Apr 6, 2010
clarify me with ulimit output and memory limit?
ulimit -a output:
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) 1572864
[code]...
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Nov 4, 2010
As i undertsand - out of 1GB of the virtual Address space for Kernel from 3GB to 4GB of the process address space, Kernel image (code, data, bss, stack, heap) resides staring @0x0 address. Vmalloc area starts either at the end of Physical ram size or at 896M. This 896M cap is mandated to ensure that minimum of 128MB is reserved as vmalloc_reserve for vmalloc,kmap etc.
Is the understanding correct? Now trying to map Physical Zones into this 1GB address space
Initial 16MB is mapped to ZONE_DMA
16MB - 896MB is mapped to ZONE_NORMAL
896MB - 1024MB is mapped to ZONE_HIGHMEM
Does this mean that Kernel image is residing in ZONE_DMA area? Any call to vmalloc() in kernel code will return address beyond 896M? insmod of any LKM will internally invoke vmalloc() to obtain contiguous area - where will this code physically located along with rest of kernel code in ZONE_DMA or in ZONE_HIGHMEM?
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Oct 25, 2010
I'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?
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Jun 27, 2010
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().
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Jul 12, 2010
what difference between user and kernel space.
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Nov 11, 2010
cusexmp, 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.
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Jul 14, 2011
I'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.
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May 3, 2010
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..
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Jul 25, 2010
I have 160gb laptop. i installed vista in c primary partition which is 25gb and installed ubuntu in d primary partition which is 20gb. A remainig for my data. Now i tried to install CENT OS by formatting ubuntu. I inserted CENT OS DVD and restarted and i selected to delete my /dev/sda2 which is showing 20480mb and it shown me free space. but i tried to add partion /boot of 100mb it got added. but, when i am trying to add / of 3000mb in the remaining 20380mb free space it showing an error message that no free space is available.
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Jul 26, 2010
I just mounted my drobo(NTFS) on my slackbox using NTFS-3g, and I can read all my files and see them all, but any file name with a space in it turns into EX: (File Name)... instead of (File Name)I am worried that my Sync software will not recognize the name.Does anyone have any tips Except to not put Spaces in the names of files?
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Jul 4, 2011
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?
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Oct 27, 2010
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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Sep 8, 2010
I sort of asked this question in the arch linux forums since I was interested in arch but I still have yet to get a response (maybe it's too early).I wan't something like gentoo but without taking up unnecessary space like gentoo's portage does (/usr/portage/). I find that to be a serious flaw with gentoo. Yes you can use squashfs-unionfs to help but it requires some work especially when something goes wrong with portage.I was thinking about arch but can you use it completely as a source based distro? Some people seem to have said it requires scripting and some work from the user. I wan't something that'll do it for me so I can set it and forget it.
I heard about source mage linux and exherbo but I'm not sure what to think. I'm thinking about trying arch linux and source mage but perhaps there's other distro's I don't know about. I'd really like some suggestions.
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Mar 19, 2010
i'm in search of Script that sends a mail to the user if the mount point goes beyond 80% of its full space.
send mail is configured in the system so that it can communicate with mail server.
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Jan 20, 2011
cp: writing `/tmp/tmpX2KZDc/system.image': No space left on device However, when I right-click on properties, I see it has 51 items, totalling only 130.5 KB!this is a dual boot system with Win XP and Ubuntu 10.10 (~58Gb partition)Quote:
anil@anil-HP-EliteBook-8440p:/tmp$ mount
/dev/sda5 on / type ext4 (rw,errors=remount-ro,commit=0)
proc on /proc type proc (rw,noexec,nosuid,nodev)
[code]...
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Nov 2, 2010
Are there any tools to view/edit user space memory of running processes on Linux?
It would be a great learning tool.
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