Loading ramdisk to memory

General Discussion
1

Hi,

I am using Beaglebone Black Rev. C. I have a ramdisk image provided by swupdate. Using uboot I load the ramdisk image to RAM, using,

load mmc 0:4 0x90000000 swupdate-ramdisk
bootz 0x82000000 0x90000000

Here is the output of the above command.

Loading init Ramdisk from Legacy Image at 0x90000000
Image Name: swupdate-image-…
Created:
…
Starting Kernel…

Then it loads the kernel. But I would like to access the environment in initrd and do some operation, like creating a file etc. How do I do that? I am not that well versed with ramdisk, so do not mind the ambiguity in my understanding(if any).

Thanks in advance for your help.

Regards,
Sai Kiran.

2

you need to do file operations during the boot process? or after … your question is not quite clear. Where are you mounting this ramdisk?

do you know about /dev/shm? it is a ramdisk that gets created for you … here is an example from my system:

gomer@bbb42:~$ df
Filesystem     1K-blocks    Used Available Use% Mounted on
udev              220000       0    220000   0% /dev
tmpfs              49492    5468     44024  12% /run
/dev/mmcblk1p1   3647540 2865840    576696  84% /
tmpfs             247444       0    247444   0% /dev/shm
tmpfs               5120       0      5120   0% /run/lock
tmpfs             247444       0    247444   0% /sys/fs/cgroup
tmpfs              49488       0     49488   0% /run/user/1001
gomer@bbb42:~$ cat /etc/dogtag
BeagleBoard.org Debian Image 2018-10-07
gomer@bbb42:~$ uname -a
Linux bbb42 4.14.71-ti-r80 #1 SMP PREEMPT Fri Oct 5 23:50:11 UTC 2018 armv7l GNU/Linux
gomer@bbb42:~$ ls -l /dev/shm
total 0
gomer@bbb42:~$ echo foo > /dev/shm/foo
gomer@bbb42:~$ ls -l /dev/shm
total 4
-rw-r--r-- 1 gomer gomer 4 Sep 29 13:20 foo
gomer@bbb42:~$ cat /dev/shm/foo
foo
gomer@bbb42:~$

I don’t know at what point during the boot process that /dev/shm gets created if that makes any difference… is it important to do the file operations during the boot process?

gomer

3

I want to do file ops, before the Linux is booted. swupdate in initrd, does some checks and boots. I would like to add some script in initrd. But the initrd file provided by swupdate is not mountable. So, I was thinking about adding the script once the u-boot loads initrd(before booting Linux).

I am not sure if this works…but would like to try. So, I was thinking about doing the file ops in initrd environment(as the system is booting).

I am not aware of /dev/shm. Will look into it. Thanks for the pointer.