Programming :: How To Do A Direct Memory Access
Jul 26, 2011
I have a single board computer previously running DOS. I recently made Linux running on it. Now that the system is running Linux, I have to translate the code that was supported by DOS. The code has segments that allow direct access of memory mapped registers through the macro _MK_FP and do read/write. I have read that where DOS allows this kind of direct memory access, Linux does not. Is there a way to do this in Linux?
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Dec 13, 2010
I am implementing c program to access ext3 file system's metadata. I want to know how to access members of the in-memory superblock structure. I am able access on-disk ext3_super_block structure but dont know how to access in- memory structure and its members.
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Jul 31, 2010
I have been looking for a method for a while now that would allow me to access another process's memory without causing it to freeze. But with all of my googling I have found nothing
so, my question is: Is there a way to not lock a process while accessing it's "/proc/[PID]/mem" interface?
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Jul 11, 2011
Kernel 2.6.21.5, slackware 12.0
nasm 2.03.01
ld 2.17
GNU gdb 6.6
This GDB was configured as "i486-slackware-linux".
Code:
What could the cause of the message output by gdb possibly be? Reading some tutorials, I've learn the flat memory model is used in linux. So, in particular, I needn't care about the DS segment register.
Also, line 7 in the listing above, suggests nasm is assuming 32-bit addressing and so, I think it is using the flat memory model.
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Jul 13, 2010
How can one have direct access to key strikes. Normally the key strikes that collected by the concerned programme and access to the same is not available to any other user programs. I am trying to write a program to simultaneously catch the key strikes. Obviously for this would require a low-level access to the keyboard. How can one do it ?
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Mar 5, 2011
Running Ubuntu Netbook remix on a Toshiba NB500-upgraded to 2 Gigabytes RAM. Very slow opening applications via the side icons. 8-12 seconds. Is that normal for this distro?
- No 3D cube. Installed related compiz software, adjusted settings, ticked cubes etc. Not a peep.
- No direct desktop access. Only via side icons. Just find it fiddly re: using desktop and changing background via side icons.
Couple other items (MBB for one) but for another category.
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Apr 22, 2010
Does a mailserver have to have direct access to WAN or can it be a LAN device with just one NIC ?
We have two WAN access points.
One is an adsl router joined to the switch and all seems fine for internet browsing.
The other is a wireless system with a linksys router joining by way of PPPoE and this appears to connect fine.
This PPPoE is direct to our ISP and where we need to downlod our mail to our pending mailserver.
When the linksys router is also joined to the switch all devices can use either the adsl or linksys to roam the net. 192.168.1.1 linksys & 192.168.1.10 is adsl.
When I join the linksys direct to the mailserver I will then need two NIC's. One for the Linksys and one for the LAN.
This is where the fun has started.
So.... Can I just have one NIC (connected to the switch) on the mailserver?
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Jun 8, 2010
I've got an Hitachi Deskstar 164GB IDE drive which I've somehow managed to upset while attempting to swap distros. I'm guessing its lost the MBR as I can't get a PC to see it except in the BIOS. The BIOS tells me that the primary master has 164GB, Cylinders 65535, Head 16, Precomp 0, Landing zone 65534 and Sector 255. (my understanding of that info is very limited). The PC won't boot direct from the hdd and a live Knoppix disc can't see it. Trying fdisk -l produces no list. (Naturally, I can't install another distro on it either).
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Jul 8, 2011
I am using a Dell Inspiron 14R laptop that came with Windows 7 Home Basic. The partitions of my hard disk before installing Fedora 15 were:
Dell (OEM Partition)
OS (C: ) (Primary Partition)
RECOVERY (Primary Partition)
New Volume (E: ) (Logical Drive)
I tried shrinking my C: drive (which has Windows) but couldn't do so hence performed the procedure on E: instead. I did this to create a 15GB unformatted space to install Fedora in. While installing Fedora, I chose the option "Use Free space" under Disk Partitioning Setup but the OS got installed in E: drive. Currently, I am able to use both Windows and Fedora under dual-boot but the problem I am facing is that when working with Windows, I am unable to see drive E: in Computer.
Windows Disk Manager is able to detect the partition and is showing it to be healthy (1st screenshot). Its name now is New Volume and neither am I able to change its path or letter (Error: incorrect parameters) nor am I able to check it using "chkdsk" (Error: cannot open volume for direct access/ GUI doesn't work as well) (2nd screenshot). On the other hand, I am able to access both the partitions in Fedora.
Another point to mention is that after finishing the installation of Fedora, when I started Windows, the Disk Manager as well as Dell DataSafe showed that the Windows Recovery drive had been formatted (maybe inappropriate terminology!) and was no longer retrievable. To rectify this problem, I restored my Windows to before Fedora was installed and I seem to have got the Recovery drive back (1st screenshot) (before doing this, it was nameless and empty).
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Oct 5, 2010
Normally all I/O goes through the kernel so that it can schedule the operations and prevent processes from stepping on each other. A few special user processes are allowed to slide around the kernel, usually by being given direct access to I/O ports. X servers are the most common example of this isn't it ? give examples for any other processes that are allowed to slide around the kernel ?
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Oct 23, 2010
I would like to access/print a C Variable of any type "as it is stored in the memory". I would expect the output to be an array of bits. Whats the simplest/shortest way to do that?
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Jun 13, 2010
i have the following system in my lan.
firewall(iptables)
etho(private) - 192.168.2.1
eth1(public) -189.117.57.2
squid server at 192.168.2.10
my request is that i have to make all out bound internet connection should go from proxy server , not directly to firewall. Please specify a iptable rule for blocking direct internet access. my clients ip ranges from 192.168.2.20 to 192.168.2.47
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Dec 17, 2008
When I try to access at physical address (0xD0000), we known that it is necessary to convert physical address to virtual address using function IOREMAP(0xD0000, 1024) and return me 0xC00D0000.
Now our doubt is when I have a board with I/O in address 0x150, is it necessary to convert this address to other virtual address??? or with inb(0x150) return me state of I/O in this address? How can I known where is this I/O address in my map memory?
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Nov 21, 2010
I am in China, where some web sites(....., facebook, etc) are blocked. So I have to access these blocked site by VPN. But how can I access blocked sites by VPN and unblocked sites by my direct ADSL?
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Feb 17, 2009
How to re-direct image
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Mar 21, 2011
I am new to C and linux. My code below does arbitary writes but I cant figure out where or how it does it.
I am calling the insertNode() function with seq = 'MISSISSPPI$' and alphabets = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ$'
Code:
Weird behaviour I should mention is that when I check for NULL pointer in node->child[index], the unassigned values are not null anymore, they point to arbitary memory.
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Apr 13, 2010
How do I write a script for my Linux that can show me total memory vs used memory and have it email me results if it's over 70 percent?
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Feb 27, 2011
I need to re-direct the output within an awk script, but not to already known, fixed filenames. The output file names depend on values of the fields. For example (the actual problem is surely more complicated), if, on a given line, the second field is DATA, the third is 1984, I would like to print some information in a file called output_DATA_1984. This could/would change in the following line of the same input file. Such things are pretty easy in bash, put I cannot do it in awk, as I can only find manual references for redirecting output to fixed filenames between double quotes.
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May 31, 2011
Any one using php program to direct lpt port print command, now i am creating one programe for mini shope that system having citizen CT-S4000 model.
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Aug 25, 2010
Is that possible that SHM shared memory is counted as cache memory on Linux with kernel 2.6.18?If find it really odd since this memory is not file backed, but I have a piece of code that loads data using shm_open+mmap, and it generates an amount of cache memory in /proc/meminfo that corresponds exactly to the amount of shared memory (I load that data from a file but I am using posix_fadvise(fd,0,0,POSIX_FADV_DONTNEED) to ensure this file is not cached and I made sure that it is working as expected). As far as I know SHM memory was not tagged as cache memory with kernel 2.6.9.If it is the case it is really unfortunate since normally cache memory can be considered to be part of the "available" memory since it can be flushed promptly but this is clearly not the case with SHM memory... Is there an easy way to get the total amount of used SHM memory on a system?
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Mar 26, 2010
I'm trying to pull out sections from a bunch of files. For one file, I use:
Code:
sed '/string1/,/string2/ !d' <filename.ext >newfilename.ext
to pull out everything between two strings in the original file and put them in a new file.
[code]....
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May 28, 2010
How to Write a small shell script that adds an extension ".new" to all the files in a directory.
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Jan 2, 2010
how do i access the files on my blackberry's memory card? also is there a way to see ALL the files (like the system files and everything) on the phone?
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Dec 29, 2010
Have downloaded ubuntu (because my linux lite died). Very pleased so far with ubuntu, but I can't figure out how to access files or photos from a memory card. Just can't seem to go to anything that even shows its existence.
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Feb 21, 2010
A process is trying one access to memory, for example through an array (ex.: vect[0]=123. What happens?
Here below what I guess but I'm not sure and accept any comment (please, distinguish between "the system" and "the CPU" in case).
Let's suppose swapping to disk disbled.
We have two scenarios: without and with cache.
If no cache is present in the system:
1. The CPU must discover the phys addr of vect[0] virtual addr. To do that, has to read from 3 (or 2 depending on the system?) pages tables, stored in memory as well.
2. The CPU writes to the final address.
These mean 4 memory accesses.
If cache is present:
1. Like above but, if the pages tables are in cache, we have 3 accesses to that.
2. If the req. page is not in cache, it's reads from ram and transferred to it. Afterwards, cache is written.
In the best case we have 4 cache accesses.
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Dec 22, 2014
How to limit access flash memory (read / write) for users on debian?
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Sep 5, 2010
recently I stumbled upon the fact you can buy a Sony Ps2 to Ps3 memory adapter which is a USB device that plugs into your PS3. However what I was wanting to know is there a way to mount the PS2 Memory card under Ubuntu via the USB device. Do I need to install a PC/SC card driver as its flash memory or do I need to use CCID?? Is it usbmount or pmount? I am a little clueless how you would get Ubuntu to read & access a PS2 Flash Card. The memory cards are manufactured by MagicGate and they bear this legend on the back; This device complies with part 15 of the FCC rules & regs and the Canadian ICES-003 operation is covered by the following conditions,
1> This device may not cause harmful interference.
2> This device must accept any interference received. Including interference that may cause undesired operation.
The way I look at it is as follows, if these memory cards are now defunct and no longer supported by Sony as such an 8mb memory card makes for a cheap storage method. Especially when people are throwing them away! The Venom adapter's are available on eBay. Let the hilarity ensue, mail your friend's some files on a 8-MB Ps2 Memory Card, then laugh with evil glee when they cant open it.
$ lsusb
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 004: ID 054c:02ea Sony Corp. <-- ah ha!
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Apr 11, 2011
By default, when applications run, they are limited in the amount of RAM they are allowed to access right? Technically my VLC could not access memory addresses used by Chrome. But how is it possible for the operating system/compiler to mistakingly allow access to an address a code is not allowed. I know alot of 'exploits' and 'payloads' take advantage of this fact and create variables that take up too much space and 'overflow' into other addresses, but how does this actually happen?
Are some programs more prone to this than others? Does it matter in which language they are coded in? For example, I know C is allowed to play around with memory, while Java is not. Also, what are the advantages of this? What if someone wrote malicious code to access someplace in memory, what could they do? The only thing I can think of is passwords/keys stored in RAM.
PS I thought about putting this in Stack Overflow, but my question is much broader than just specifically related to a programming perspective. If I've placed it in the wrong place, I'm sorry.
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Mar 3, 2011
I'm currently developping a program in C++, using Qt, for an embedded board (SBC9261).It works well but crashes after some time, due to a system memory overload (my program uses more and more memory until 100%, when it crashes).I've been able to figure out the source of the memory leak :The function f is called by my program every second. f instanciates a new object (a QImage from the Qt lib), does a bunch of processing on it, and returns it to the calling function :
Code:
QImage *MyClass::f(QString filename) {// Open image
QImage *image = new QImage(filename);
[code]....
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Jul 22, 2011
I have a general question regarding memory errors. I frequently ran into memory errors such as seg fault, double free, etc. Sometimes I got the following traces for example.
*** glibc detected *** /mnt/click: free(): invalid pointer: 0xb7ed8450 ***
======= Backtrace: =========
/lib/libc.so.6[0xb7dff905]
/lib/libc.so.6[0xb7e011a3]
[code]....
Then, I just run gdb, valgrind things and suddenly I started ask questions myself that what are those traces and how can I analyze?
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