Re: [PATCH RFC 2/3] xen/domain: add domain hypfs directories

[Julien Grall <julien@xen.org>]

Hi Juergen,

On 09/12/2020 16:16, Juergen Gross wrote:
> Add /domain/<domid> directories to hypfs. Those are completely
> dynamic, so the related hypfs access functions need to be implemented.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> V3:
> - new patch
> ---
>   docs/misc/hypfs-paths.pandoc |  10 +++
>   xen/common/Makefile          |   1 +
>   xen/common/hypfs_dom.c       | 137 +++++++++++++++++++++++++++++++++++
>   3 files changed, 148 insertions(+)
>   create mode 100644 xen/common/hypfs_dom.c
> 
> diff --git a/docs/misc/hypfs-paths.pandoc b/docs/misc/hypfs-paths.pandoc
> index e86f7d0dbe..116642e367 100644
> --- a/docs/misc/hypfs-paths.pandoc
> +++ b/docs/misc/hypfs-paths.pandoc
> @@ -34,6 +34,7 @@ not containing any '/' character. The names "." and ".." are reserved
>   for file system internal use.
>   
>   VALUES are strings and can take the following forms (note that this represents
> +>>>>>>> patched

This seems to be a left-over of a merge.

>   only the syntax used in this document):
>   
>   * STRING -- an arbitrary 0-delimited byte string.
> @@ -191,6 +192,15 @@ The scheduling granularity of a cpupool.
>   Writing a value is allowed only for cpupools with no cpu assigned and if the
>   architecture is supporting different scheduling granularities.
>   

[...]

> +
> +static int domain_dir_read(const struct hypfs_entry *entry,
> +                           XEN_GUEST_HANDLE_PARAM(void) uaddr)
> +{
> +    int ret = 0;
> +    const struct domain *d;
> +
> +    for_each_domain ( d )

This is definitely going to be an issue if you have a lot of domain 
running as Xen is not preemptible.

I think the first step is to make sure that HYPFS can scale without 
hogging a pCPU for a long time.

Cheers,

-- 
Julien Grall