Am 29.10.2022 um 14:20 hat Alberto Faria geschrieben: > Some libblkio drivers may be able to work with regular files (e.g., > io_uring) or otherwise resizable devices. Conservatively set > BlockDriver::has_variable_length to true to ensure bdrv_nb_sectors() > always gives up-to-date results. > > Also implement BlockDriver::bdrv_co_truncate for the case where no > preallocation is needed and the device already has a size compatible > with what was requested. > > Signed-off-by: Alberto Faria <afa...@redhat.com> > --- > > This is based on Stefan's block tree: > https://gitlab.com/stefanha/qemu/-/commits/block > > block/blkio.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/block/blkio.c b/block/blkio.c > index 82f26eedd2..190454cdbe 100644 > --- a/block/blkio.c > +++ b/block/blkio.c > @@ -845,6 +845,31 @@ static int64_t blkio_getlength(BlockDriverState *bs) > return capacity; > } > > +static int coroutine_fn blkio_truncate(BlockDriverState *bs, int64_t offset, > + bool exact, PreallocMode prealloc, > + BdrvRequestFlags flags, Error **errp) > +{ > + int64_t current_length; > + > + if (prealloc != PREALLOC_MODE_OFF) { > + error_setg(errp, "Unsupported preallocation mode '%s'", > + PreallocMode_str(prealloc)); > + return -ENOTSUP; > + } > + > + current_length = blkio_getlength(bs); > + > + if (offset > current_length) { > + error_setg(errp, "Cannot grow device"); > + return -EINVAL; > + } else if (exact && offset != current_length) { > + error_setg(errp, "Cannot resize device"); > + return -ENOTSUP; > + } > + > + return 0; > +} > + > static int blkio_get_info(BlockDriverState *bs, BlockDriverInfo *bdi) > { > return 0; > @@ -960,10 +985,12 @@ static void blkio_refresh_limits(BlockDriverState *bs, > Error **errp) > { \ > .format_name = name, \ > .protocol_name = name, \ > + .has_variable_length = true, \
I don't think this is a good idea, it will read the capacity from libblkio before every single request, which can't result in good performance. We're generally only using .has_variable_length for removable media on the backend (i.e. for host_cdrom and filters that can potentially sit on top of it, but will used the cached value on the protocol level again for other protocol drivers). If you resize a host_device, you need to use QMP 'block_resize' explicitly. I think it should be the same for libblkio. Kevin
