Re: [PATCH v15 3/8] block: add block layer APIs resembling Linux ZonedBlockDevice ioctls

[Stefan Hajnoczi]

On Mon, Feb 27, 2023 at 07:20:14PM +0100, Kevin Wolf wrote:
> Am 29.01.2023 um 11:28 hat Sam Li geschrieben:
> > Add zoned device option to host_device BlockDriver. It will be presented 
> > only
> > for zoned host block devices. By adding zone management operations to the
> > host_block_device BlockDriver, users can use the new block layer APIs
> > including Report Zone and four zone management operations
> > (open, close, finish, reset, reset_all).
> > 
> > Qemu-io uses the new APIs to perform zoned storage commands of the device:
> > zone_report(zrp), zone_open(zo), zone_close(zc), zone_reset(zrs),
> > zone_finish(zf).
> > 
> > For example, to test zone_report, use following command:
> > $ ./build/qemu-io --image-opts -n driver=host_device, filename=/dev/nullb0
> > -c "zrp offset nr_zones"
> > 
> > Signed-off-by: Sam Li <faithilikerun@gmail.com>
> > Reviewed-by: Hannes Reinecke <hare@suse.de>
> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> >  block/block-backend.c             | 147 ++++++++++++++
> >  block/file-posix.c                | 323 ++++++++++++++++++++++++++++++
> >  block/io.c                        |  41 ++++
> >  include/block/block-io.h          |   7 +
> >  include/block/block_int-common.h  |  21 ++
> >  include/block/raw-aio.h           |   6 +-
> >  include/sysemu/block-backend-io.h |  18 ++
> >  meson.build                       |   4 +
> >  qemu-io-cmds.c                    | 149 ++++++++++++++
> >  9 files changed, 715 insertions(+), 1 deletion(-)
> > 
> > diff --git a/block/block-backend.c b/block/block-backend.c
> > index ba7bf1d6bc..a4847b9131 100644
> > --- a/block/block-backend.c
> > +++ b/block/block-backend.c
> > @@ -1451,6 +1451,15 @@ typedef struct BlkRwCo {
> >      void *iobuf;
> >      int ret;
> >      BdrvRequestFlags flags;
> > +    union {
> > +        struct {
> > +            unsigned int *nr_zones;
> > +            BlockZoneDescriptor *zones;
> > +        } zone_report;
> > +        struct {
> > +            unsigned long op;
> > +        } zone_mgmt;
> > +    };
> >  } BlkRwCo;
> 
> Should we use a different struct for blk_aio_zone_*() so that we don't
> need to touch the one for the normal I/O path? My concern is that
> increasing the size of the struct (currently 32 bytes) might negatively
> impact the performance even of non-zoned devices. Maybe it turns out
> that it wasn't really necessary in the end (have we done any
> benchmarks?), but I don't think it can hurt anyway.
> 
> With this changed, you can add to the series:
> Acked-by: Kevin Wolf <kwolf@redhat.com>

There are unused fields in BlkRwCo and BlkAioEmAIOCB, so changing the
size of the struct isn't necessary. ioctl/flush/pdiscard already use
BlkAioEmAIOCB/BlkRwCo for non-read/write operations, including using the
iobuf field for different types, so it wouldn't be weird:

  typedef struct BlkRwCo {
      BlockBackend *blk;
      int64_t offset;
      void *iobuf;
            ^^^^^ used for preadv/pwritev qiov, ioctl buf, and NULL for
                  other request types. zone_report could put the
                  BlockZoneDescriptor pointer here. zone_mgmt could put
                  op here.
      int ret;
      BdrvRequestFlags flags;
  } BlkRwCo;

  typedef struct BlkAioEmAIOCB {
      BlockAIOCB common;
      BlkRwCo rwco;
      int64_t bytes;
              ^^^^^ zone_report could put the nr_zones pointer here
      bool has_returned;
  } BlkAioEmAIOCB;

Does that sound okay?

Stefan

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