Re: xenstore utils dropped support for -s in 4.15

[Henrik Riomar <rio@riomar.se>]

On Sun, 11 Apr 2021 11:17:38 +0200
Juergen Gross <jgross@suse.com> wrote:

> On 11.04.21 09:17, Henrik Riomar wrote:
> > On Sun, 11 Apr 2021 07:34:16 +0200
> > Juergen Gross <jgross@suse.com> wrote:
> > 
> >> On 11.04.21 00:02, Henrik Riomar wrote:
> >>> Hi,
> >>>
> >>> In Alpine and Debian (probably elsewhere as well), the -s flag removed in these two commits:
> >>>    * https://github.com/xen-project/xen/commit/fa06cb8c38832aafe597d719040ba1d216e367b8
> >>>    * https://github.com/xen-project/xen/commit/c65687ed16d2289ec91036ec2862a4b4bd34ea4f
> >>> is actually used in the init scripts.
> > 
> >>> Reverting the two commits mentioned above restores a booting system.
> >>>
> >>> The -s flag was introduced in 2005 or so, so I guess you can say that dropping it should
> >>> at least be mentioned in the release notices, and an alternative be described, or
> >>> -s functionally should be brought back.
> >>
> >> The -s served exactly no purpose.
> > 
> > yes its used by dists to check that the socket is actually accessible (without falling back to
> > direct access to /dev/xen/xenbus).
> 
> There are Xen configurations where the socket is never accessible,
> as it is not existing.

sure, but this is in the start script for the daemon it self we use "xenstore-read -s /"
so it will also work if that script is used in a domain only running xenstored, right?

> 
> >> It was meant to force socket usage. A socket will be used anyway in
> >> case xenstored is running in dom0, so specifying -s won't change
> >> anything in this case.
> > 
> > yes reverting the to commits above and using -s, brings back the original behavior, returning
> > with failure if the socket is not there.
> 
> And returning failure when Xenstore is running fine, but not in dom0.

sure, -s means access via local socket so yes.

> 
> > There are two issues here I think:
> >   1. dists actually use -s to check if the daemon is up (and been doing this for a long time)
> 
> This should be changed, as it is based on wrong assumptions.

changed to what exactly? check for a pid file? that also only works locally just like
-s.

> 
> >   2. Reads of /dev/xen/xenbus (via xenstore-read -s /), blocks for ever in 4.15
> 
> So you are basically saying that you'd like to have a test "is Xenstore
> running", and this test should work with the "-s" flag.
> 
> I can look into that, but reverting the "access via socket" removal flag
> is not the way to go.
> 

Ok, so what should dists packaging 4.15 do? can the release notices be updated with this?

Thanks,
 Henrik