Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Tue, 2 Feb 2021 08:40:51 -0800

On 2/2/21 8:21 AM, Siddons, David wrote:
> Hi David,
>   I believe I'm hitting the same issue. In an embedded IOC I need to access /dev/mem, which requires privilege. The system is Debian 10, on a ZynQ processor. I want to run this IOC as a regular user, not root. I tried setcap, but always get:
> 
> Failed to get capabilities of file `./regrw' (Operation not supported)
> whatever file I try it on.
> 
> I also tried putting the user in the kmem group, like /dev/mem:
> 
> ls -l /dev/mem                                      
> crw-r----- 1 root kmem 1, 1 Feb  1 21:05 /dev/mem
> 
> groups hera                                          
> hera : hera kmem sudo i2c
> 
> Although that worked for /dev/i2c, it did not for /dev/mem. Is this a symptom of what you described? How do I fix it?

This looks like a different issue.  You mention ZynQ.  Are using using a custom Linux kernel build?
If so, you probably don't have all of the configuration options needed.  eg. file capabilities are
stored as extended attributes, so you will need to compile in support for XATTRS for whatever
filesystems you are using.

> $ grep XATTR /boot/config-5.9.0-0.bpo.5-amd64 
> CONFIG_REISERFS_FS_XATTR=y
> CONFIG_F2FS_FS_XATTR=y
> CONFIG_TMPFS_XATTR=y
> CONFIG_JFFS2_FS_XATTR=y
> CONFIG_UBIFS_FS_XATTR=y
> CONFIG_SQUASHFS_XATTR=y
> CONFIG_EROFS_FS_XATTR=y
> CONFIG_CIFS_XATTR=y

I'm not certain what all options are needed.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System