I would like to add a small enhancement to the OS, and need to store 4 bytes-Where?

DavidKimbl · 05-28-2015, 12:24 PM

Hi,

As in the subject line, is there at least 4 bytes of low storage available which I could update continuously, (like in a high-priority background program) and this would then be available to any program running.

Does anyone know where this data would best be stored? I was hoping there is already some such area just for developers to use. But I'm pretty new to linux... is there a memory map of the kernel which I should look at?

Anything you can suggest will be greatly appreciated.

David K

veerain · 05-29-2015, 12:11 AM

You can make a ramdisk for that storage.

trevoratxtal · 05-29-2015, 02:51 AM

this may help

https://wiki.archlinux.org/index.php...ment_variables

Trev

ondoho · 05-30-2015, 06:45 AM

an environment variable could be a good solution.
otherwise, open a terminal and type "mount" - chances are you already have a RAM partition:

Code:

run on /run type tmpfs (rw,nosuid,nodev,relatime,mode=755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
tmpfs on /tmp type tmpfs (rw)
tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=740668k,mode=700,uid=1000,gid=100)

typically you would use /tmp or /dev/shm.

of what nature is this 4 byte data?

veerain · 05-30-2015, 08:24 AM

Quote:

Originally Posted by ondoho

an environment variable could be a good solution.
otherwise, open a terminal and type "mount" - chances are you already have a RAM partition:

typically you would use /tmp or /dev/shm.

tmpfs is not ram partition/block. It is a ram based filesystem. Also data on it it can be swapped to swap space.

DavidKimbl · 06-01-2015, 07:54 AM

Thanks to all of you for your helpful suggestions!! I'm pretty sure a RAM disk is not what I'd be lloking for, but the Environment Variable may work well. It would be 4-bytes of binary data Similar in nature to when programs refer to the Real Time Clock now.
I was envisioning some 4-bytes of low storage or CMOS storage which is currently unused (or at least not used for anything important)
(like the High Memorty address--ha).

David --- Long Live Linux

ondoho · 06-08-2015, 09:56 AM

Quote:

Originally Posted by DavidKimbl

the Environment Variable may work well. It would be 4-bytes of binary data Similar in nature to when programs refer to the Real Time Clock now.

i'm not sure if you can assign binary data to an environment variable?

Quote:

I was envisioning some 4-bytes of low storage or CMOS storage which is currently unused

wow, that's pretty close to the hardware.
i have no idea how something like that could even be done in linux. sounds more like bios stuff to me.

trevoratxtal · 06-08-2015, 11:29 AM

hello ondoho
Ref Environment variable and storage please read
http://www.linuxnix.com/2012/05/conv...linuxunix.html
or Google ""linux shell hex to binary"", there are many ways to solve a problem in Linux using shell!
I believe you can put what you like in a variable 16 32 and 65 bit.
Trev

ondoho · 06-08-2015, 12:43 PM

@trevoratxtal, thanks for that link. however, i think "binary" in that article means an actual string of 1's and 0's, but i think op meant actual binary data, as in "a pile of bits, clustered into bytes".
i recently had a similar problem...
as an illustration, try

Code:

cat /dev/urandom

(that's my definition of binary data)

but you got me thinking, and i think there's a utility that will convert that to something bash can use.

Code:

cat /dev/urandom | base64 -i -w 0

maybe...

i'm not saying i'm right or you're wrong, just thinking out...

in the end it depends on the nature of op's data.

273 · 06-08-2015, 12:56 PM

It this fixed or variable data? You could name your kernel in hex and use uname to reach it...
I'll admit to being well out of my depth code wise but how about creating a device node? If it's fFast enough for device access. Oh, sorry, I see that suggested above, I think.