Hi,
I use shared memory in order to control a robotic system through a special ISA board.
I followed these steps :
1. I wrote "append "mem=63m" " in lilo.conf
2. I created the device : mknod /dev/mymem c 1 2
3. I wrote the RT kernel module which read/write the shared memory in order to control
the ISA board
4. I wrote the user-space program which mmap the shared memory in ordre to communicate
with the previous module
Everything works perfectly when executed as root !
Nevertheless, because the robotic system has to be used by students, I try to run the
user-space application as user :
1. I created a group memaccess
2. I added the user "student" to this new group.
3. I changed the group of /dev/mymem : chgrp memaccess /dev/mymem
4. I added the R/W group permissions : chmod g+rw /dev/mymem
the ls -l command gives the following result :
=> /dev/mymem crw-rw-r-- root memaccess
But, when trying to open "/dev/mymem" when logged as student i had "a permission
denied" error. I don't understand why...
Any help will be welcomed ?
Thanks.
Cyril.
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