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Re: [PATCH v2] machine: add missing doc for memory-backend option
From: |
Igor Mammedov |
Subject: |
Re: [PATCH v2] machine: add missing doc for memory-backend option |
Date: |
Wed, 20 Jan 2021 11:20:50 +0100 |
On Fri, 15 Jan 2021 10:36:05 +0100
Michal Privoznik <mprivozn@redhat.com> wrote:
> On 1/15/21 12:46 AM, Igor Mammedov wrote:
> > Add documentation for '-machine memory-backend' CLI option and
> > how to use it.
> >
> > And document that x-use-canonical-path-for-ramblock-id,
> > is considered to be stable to make sure it won't go away by accident.
> >
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> > v2:
> > - add doc that x-use-canonical-path-for-ramblock-id is considered stable,
> > (Peter Krempa <pkrempa@redhat.com>)
> > ---
> > backends/hostmem.c | 10 ++++++++++
> > qemu-options.hx | 28 +++++++++++++++++++++++++++-
> > 2 files changed, 37 insertions(+), 1 deletion(-)
> >
>
>
> > @@ -96,6 +97,31 @@ SRST
> > ``hmat=on|off``
> > Enables or disables ACPI Heterogeneous Memory Attribute Table
> > (HMAT) support. The default is off.
> > +
> > + ``memory-backend='id'``
> > + An alternative to legacy ``-mem-path`` and ``mem-prealloc``
> > options.
> > + Allows to use a memory backend as main RAM.
> > +
> > + For example:
> > + ::
> > + -object
> > memory-backend-file,id=pc.ram,size=512M,mem-path=/hugetlbfs,prealloc=on,share=on
> > + -machine memory-backend=pc.ram
> > + -m 512M
> > +
> > + Migration compatibility note:
> > + a) as backend id one shall use value of 'default-ram-id',
> > advertised by
> > + machine type (available via ``query-machines`` QMP command)
> > + b) for machine types 4.0 and older, user shall
> > + use ``x-use-canonical-path-for-ramblock-id=on`` backend option
> > + (this option must be considered stable, as if it didn't have the
> > 'x-'
> > + prefix including deprecation period, as long as 4.0 and older
> > machine
> > + types exists),
> > + if migration to/from old QEMU (<5.0) is expected.
> > + For example:
> > + ::
> > + -object
> > memory-backend-ram,id=pc.ram,size=512M,x-use-canonical-path-for-ramblock-id=on
> > + -machine memory-backend=pc.ram
> > + -m 512M
>
> Igor, this doesn't correspond with your comment in bugzilla:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1836043#c31
>
> In fact, we had to turn the attribute OFF so that canonical path is not
> used. Isn't ON the default state anyway?
indeed, it should be 'off',
>
> Michal
>
>