TESTDAY Report: Unexpected results for xenhyps

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

Playing around with the new `xenhypfs` binary, got some unexpected results:

* Unexpected error message for non-existent nodes

Command executed:

# xenhypfs cat /params/loglvlx
could not read: Operation not permitted

Expected behavior: -ENOENT-style message
Actual behavior: -EACCESS-style message

* Truncated output from /params/loglvl

root@immortal:~# xenhypfs write /params/loglvl none
root@immortal:~# xenhypfs cat /params/loglvl
none/non
root@immortal:~# xenhypfs write /params/loglvl error
root@immortal:~# xenhypfs cat /params/loglvl
error/er
root@immortal:~# xenhypfs write /params/loglvl warning
root@immortal:~# xenhypfs cat /params/loglvl
warning/

Expected behavior: Full new string printed (`none/none`, `error/error`, 
`warning/warning` respectively)

Actual behavior: Only 8 characters ever printed

* Same as above for /params/guest_loglvl


Everything else looks OK.

# xl info
xl info
host                   : immortal
release                : 5.2.0-2-amd64
version                : #1 SMP Debian 5.2.9-2 (2019-08-21)
machine                : x86_64
nr_cpus                : 8
max_cpu_id             : 31
nr_nodes               : 1
cores_per_socket       : 4
threads_per_core       : 2
cpu_mhz                : 2533.431
hw_caps                : 
bfebfbff:029ee3ff:2c100800:00000001:00000000:00000000:00000000:00000100
virt_caps              : pv hvm hvm_directio pv_directio hap shadow
total_memory           : 6141
free_memory            : 5028
sharing_freed_memory   : 0
sharing_used_memory    : 0
outstanding_claims     : 0
free_cpus              : 0
xen_major              : 4
xen_minor              : 14
xen_extra              : .0-rc
xen_version            : 4.14.0-rc
xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 
hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler          : credit2
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          :
xen_commandline        : placeholder dom0_mem=1024M,max:1024M cpuinfo 
com1=115200,8n1 console=com1,tty loglvl=all guest_loglvl=all acpi_sleep=s3_fake 
debug_synthetic_preemption=1024
cc_compiler            : gcc (Debian 9.2.1-30) 9.2.1 20200224
cc_compile_by          : root
cc_compile_domain      :
cc_compile_date        : Tue Jun  9 13:32:54 UTC 2020
build_id               : da97d170bfab3ccce05773f63cffdce3e3cc52ba
xend_config_format     : 4