Regression: [PATCH v10 10/12] tools/libxl: use libxenhypfs for setting xen runtime parameters

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 19/05/2020 08:21, Juergen Gross wrote:
> Instead of xc_set_parameters() use xenhypfs_write() for setting
> parameters of the hypervisor.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Something here isn't right.  XenServer's testing for XSA-304 has shown
the following bizarre behaviour.

# xl set-parameters ept=
libxl: error: libxl.c:701:libxl_set_parameters: setting parameters:
Invalid argument
cannot set parameters: ept=
# xl set-parameters ept=exec-sp
# xl set-parameters ept=no-exec-sp
libxl: error: libxl.c:701:libxl_set_parameters: setting parameters: No
space left on device
cannot set parameters: ept=no-exec-sp

Instrumentation shows that the first two examples here enter
parse_ept_param_runtime() with the provided string, while the third
example doesn't.

Given the -ENOSPC, I'm guessing there is some overly small internal
buffer somewhere in the hyperfs infrastructure ?

~Andrew