lindebugfs: Update fops_blob_read to operate on a kernel pointer.

[jhb]

Summary

lindebugfs allocates an intermediate kernel buffer that is passed to
the read callback rather than passing a user pointer.

Obtained from: CheriBSD
Sponsored by: DARPA

[jhb]

This is what I used locally in CheriBSD for now and might be an alternative to D37101.

[bz]

I'll have a look and give it a try and let you know.

[jhb]

Ping

[bz]

EAFNOTSUP; sorry, I'll try to give it a try within 48 hours. @jfree can you do drm testing?

[jfree]

In D38420#881831, @bz wrote:

EAFNOTSUP; sorry, I'll try to give it a try within 48 hours. @jfree can you do drm testing?

A quick grep -r "debugfs_create_blob" drm yields only two results:

amd/amdgpu/amdgpu_debugfs.c:	debugfs_create_blob("amdgpu_vbios", 0444, root,
amd/amdgpu/amdgpu_debugfs.c:	debugfs_create_blob("amdgpu_discovery", 0444, root,

Unfortunately, I do not have access to AMD hardware, so I cannot test this. It doesn't look like the debugfs blob interface is used very much in drm.