| Message ID | 20170221024248.11027-4-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Feb 21, 2017 at 6:45 AM Eric Blake <eblake@redhat.com> wrote: > The NBD protocol would like to advertise the optimal I/O > size to the client; but it would be a layering violation to > peek into blk_bs(blk)->bl, when we only have a BB. > > This copies the existing blk_get_max_transfer() in reading > a value from the top BDS; where that value was picked via > bdrv_refresh_limits() to reflect the overall constraints of > the entire BDS chain. > > Signed-off-by: Eric Blake <eblake@redhat.com> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> > > --- > v4: retitle, as part of rebasing to byte limits > v3: new patch > --- > include/sysemu/block-backend.h | 1 + > block/block-backend.c | 12 ++++++++++++ > 2 files changed, 13 insertions(+) > > diff --git a/include/sysemu/block-backend.h > b/include/sysemu/block-backend.h > index 6444e41..882480a 100644 > --- a/include/sysemu/block-backend.h > +++ b/include/sysemu/block-backend.h > @@ -174,6 +174,7 @@ void blk_lock_medium(BlockBackend *blk, bool locked); > void blk_eject(BlockBackend *blk, bool eject_flag); > int blk_get_flags(BlockBackend *blk); > uint32_t blk_get_max_transfer(BlockBackend *blk); > +uint32_t blk_get_opt_transfer(BlockBackend *blk); > int blk_get_max_iov(BlockBackend *blk); > void blk_set_guest_block_size(BlockBackend *blk, int align); > void *blk_try_blockalign(BlockBackend *blk, size_t size); > diff --git a/block/block-backend.c b/block/block-backend.c > index efbf398..4d91ff8 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -1426,6 +1426,18 @@ uint32_t blk_get_max_transfer(BlockBackend *blk) > return MIN_NON_ZERO(max, INT_MAX); > } > > +/* Returns the optimum transfer length, in bytes; may be 0 if no optimum > */ > +uint32_t blk_get_opt_transfer(BlockBackend *blk) > +{ > + BlockDriverState *bs = blk_bs(blk); > + > + if (bs) { > + return bs->bl.opt_transfer; > + } else { > + return 0; > + } > +} > + > int blk_get_max_iov(BlockBackend *blk) > { > return blk->root->bs->bl.max_iov; > -- > 2.9.3 > > > -- Marc-André Lureau
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h index 6444e41..882480a 100644 --- a/include/sysemu/block-backend.h +++ b/include/sysemu/block-backend.h @@ -174,6 +174,7 @@ void blk_lock_medium(BlockBackend *blk, bool locked); void blk_eject(BlockBackend *blk, bool eject_flag); int blk_get_flags(BlockBackend *blk); uint32_t blk_get_max_transfer(BlockBackend *blk); +uint32_t blk_get_opt_transfer(BlockBackend *blk); int blk_get_max_iov(BlockBackend *blk); void blk_set_guest_block_size(BlockBackend *blk, int align); void *blk_try_blockalign(BlockBackend *blk, size_t size); diff --git a/block/block-backend.c b/block/block-backend.c index efbf398..4d91ff8 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1426,6 +1426,18 @@ uint32_t blk_get_max_transfer(BlockBackend *blk) return MIN_NON_ZERO(max, INT_MAX); } +/* Returns the optimum transfer length, in bytes; may be 0 if no optimum */ +uint32_t blk_get_opt_transfer(BlockBackend *blk) +{ + BlockDriverState *bs = blk_bs(blk); + + if (bs) { + return bs->bl.opt_transfer; + } else { + return 0; + } +} + int blk_get_max_iov(BlockBackend *blk) { return blk->root->bs->bl.max_iov;
The NBD protocol would like to advertise the optimal I/O size to the client; but it would be a layering violation to peek into blk_bs(blk)->bl, when we only have a BB. This copies the existing blk_get_max_transfer() in reading a value from the top BDS; where that value was picked via bdrv_refresh_limits() to reflect the overall constraints of the entire BDS chain. Signed-off-by: Eric Blake <eblake@redhat.com> --- v4: retitle, as part of rebasing to byte limits v3: new patch --- include/sysemu/block-backend.h | 1 + block/block-backend.c | 12 ++++++++++++ 2 files changed, 13 insertions(+)