tmem/libxc: Squash XEN_SYSCTL_TMEM_OP_[SET|SAVE]..

tmem/libxc: Squash XEN_SYSCTL_TMEM_OP_[SET|SAVE]..

Specifically:

XEN_SYSCTL_TMEM_OP_SET_[WEIGHT,COMPRESS] are now done via:

 XEN_SYSCTL_TMEM_SET_CLIENT_INFO

and XEN_SYSCTL_TMEM_OP_SAVE_GET_[VERSION,MAXPOOLS,
CLIENT_WEIGHT, CLIENT_FLAGS] can now be retrieved via:

 XEN_SYSCTL_TMEM_GET_CLIENT_INFO

All this information is now in 'struct xen_tmem_client' and
that is what we pass around.

We also rev up the XEN_SYSCTL_INTERFACE_VERSION as we are
re-using the value number of the deleted ones (and henceforth
the information is retrieved differently).

On the toolstack, prior to this patch, the xc_tmem_control
would use the bounce buffer only when arg1 was set and the cmd
was to list. With the 'XEN_SYSCTL_TMEM_OP_SET_[WEIGHT|COMPRESS]'
that made sense as the 'arg1' would have the value. However
for the other ones (say XEN_SYSCTL_TMEM_OP_SAVE_GET_POOL_UUID)
the 'arg1' would be the length of the 'buf'. If this
confusing don't despair, patch patch titled:
tmem/xc_tmem_control: Rename 'arg1' to 'len' and 'arg2' to arg.
takes care of that.

The acute reader of the toolstack code will discover that
we only used the bounce buffer for LIST, not for any other
subcommands that used 'buf'!?! Which means that the contents
of 'buf' would never be copied back to the calleer 'buf'!

The author is not sure how this could possibly work, perhaps Xen 4.1
(when this was introduced) was more relaxed about the bounce buffer
being enabled. Anyhow this fixes xc_tmem_control to do it for
any subcommand that has 'arg1'.

Lastly some of the checks in xc_tmem_[restore|save] are removed
as they can't ever be reached (not even sure how they could
have been reached in the original submission). One of them
is the check for the weight against -1 when in fact the
hypervisor would never have provided that value.

Now the checks are simple - as the hypercall always returns
->version and ->maxpools (which is mirroring how it was done
prior to this patch). But if one wants to check the if a guest
has any tmem activity then the patch titled
"tmem: Batch and squash XEN_SYSCTL_TMEM_OP_SAVE_GET_POOL_
[FLAGS,NPAGES,UUID] in one sub-call: XEN_SYSCTL_TMEM_OP_GET_POOLS."
adds an ->nr_pools to check for that.

Also we add the check for ->version and ->maxpools and remove
the TODO.

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>