[libvirt PATCH 07/29] cpu-gather: Move msr decoding to new script

[Michal Prívozník]

On 12/15/20 5:24 PM, Tim Wiederhake wrote:
> Fixes the leaking file descriptors. Does not silently ignore errors
> (e.g. permission denied on /dev/cpu/0/msr if run as non-root) and
> always attempt to read from /dev/kvm if /dev/cpu/0/msr failed.
> 
> 'gather_msr()' returns a dictionary of values, as a later patch will
> add more registers to be interrogated.
> 
> Signed-off-by: Tim Wiederhake <twiederh at redhat.com>
> ---
>   tests/cputestdata/cpu-gather.py | 34 ++++++++++++++++++++++++++++
>   tests/cputestdata/cpu-gather.sh | 40 ---------------------------------
>   2 files changed, 34 insertions(+), 40 deletions(-)
> 
> diff --git a/tests/cputestdata/cpu-gather.py b/tests/cputestdata/cpu-gather.py
> index 75cf290a28..db2348b460 100755
> --- a/tests/cputestdata/cpu-gather.py
> +++ b/tests/cputestdata/cpu-gather.py
> @@ -1,8 +1,11 @@
>   #!/usr/bin/env python3
>   
>   import argparse
> +import fcntl
>   import os
> +import struct
>   import subprocess
> +import sys
>   
>   
>   def gather_name(args):
> @@ -38,6 +41,31 @@ def gather_cpuid_leaves(args):
>           yield line.strip()
>   
>   
> +def gather_msr():
> +    IA32_ARCH_CAPABILITIES_MSR = 0x10a
> +    KVM_GET_MSRS = 0xc008ae88
> +
> +    try:
> +        with open("/dev/cpu/0/msr", "rb") as f:
> +            f.seek(IA32_ARCH_CAPABILITIES_MSR)
> +            buf = f.read(8)
> +            msr = struct.unpack("=Q", buf)[0]
> +            return "", {IA32_ARCH_CAPABILITIES_MSR: msr}
> +    except IOError as e:
> +        print("Warning: {}".format(e), file=sys.stderr)

Previously, if /dev/cpu/0/msr was not present, then no warning was 
written. Now I get this warning, fortunately on stderr so cpu-parse.sh 
is not affected. I'm not saying it's a bad thing, these scripts are 
expected to be called by advanced users (if not developers) and this 
warning may shed more light. Just want to point out it was noticed ;-)

> +
> +    try:
> +        bufIn = struct.pack("=LLLLQ", 1, 0, IA32_ARCH_CAPABILITIES_MSR, 0, 0)
> +        with open("/dev/kvm", "rb") as f:
> +            bufOut = fcntl.ioctl(f, KVM_GET_MSRS, bufIn)
> +            msr = struct.unpack("=LLLLQ", bufOut)[4]
> +            return " via KVM", {IA32_ARCH_CAPABILITIES_MSR: msr}
> +    except IOError as e:
> +        print("Warning: {}".format(e), file=sys.stderr)
> +
> +    return None, {}
> +
> +

Michal