Re: [PATCH v4 3/4] qcow2: add zoned emulation capability

[Sam Li]

Eric Blake <eblake@redhat.com> 于2023年9月29日周五 03:17写道：
>
> On Mon, Sep 18, 2023 at 05:53:12PM +0800, Sam Li wrote:
> > By adding zone operations and zoned metadata, the zoned emulation
> > capability enables full emulation support of zoned device using
> > a qcow2 file. The zoned device metadata includes zone type,
> > zoned device state and write pointer of each zone, which is stored
> > to an array of unsigned integers.
> >
> > Each zone of a zoned device makes state transitions following
> > the zone state machine. The zone state machine mainly describes
> > five states, IMPLICIT OPEN, EXPLICIT OPEN, FULL, EMPTY and CLOSED.
> > READ ONLY and OFFLINE states will generally be affected by device
> > internal events. The operations on zones cause corresponding state
> > changing.
> >
> > Zoned devices have a limit on zone resources, which puts constraints on
> > write operations into zones.
> >
> > Signed-off-by: Sam Li <faithilikerun@gmail.com>
> > ---
> >  block/qcow2.c          | 709 ++++++++++++++++++++++++++++++++++++++++-
> >  block/qcow2.h          |   2 +
> >  block/trace-events     |   2 +
> >  docs/interop/qcow2.txt |   6 +
> >  4 files changed, 717 insertions(+), 2 deletions(-)
>
> You may want to look at scripts/git.orderfile; putting spec changes
> (docs/*) first in your output before implementation is generally
> beneficial to reviewers.
>
> > +++ b/docs/interop/qcow2.txt
> > @@ -367,6 +367,12 @@ The fields of the zoned extension are:
> >                      The maximal number of 512-byte sectors of a zone
> >                      append request that can be issued to the device.
> >
> > +          36 - 43:  zonedmeta_offset
> > +                    The offset of zoned metadata structure in the file in 
> > bytes.
>
> For the spec to be useful, you also need to add a section describing
> the layout of the zoned metadata structure actually is.
>
> > +
> > +          44 - 51:  zonedmeta_size
> > +                    The size of zoned metadata in bytes.
> > +
>
> Can the zoned metadata structure ever occupy more than 4G, or can this
> field be sized at 4 bytes instead of 8?

The zoned metadata is the write pointers of all zones. The size of it
is nr_zones (uint32_t) * write_pointer size (uint64_t). So it will not
occupy more than 4G. But it still need more than 4 bytes.

>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.
> Virtualization:  qemu.org | libguestfs.org
>