On Fri, Jan 26, 2018 at 01:34:39PM -0600, Eric Blake wrote: > We don't need the can_write_zeroes_with_unmap field in > BlockDriverInfo, because it is redundant information with > supported_zero_flags & BDRV_REQ_MAY_UNMAP. Note that > BlockDriverInfo and supported_zero_flags are both per-device > settings, rather than global state about the driver as a > whole, which means one or both of these bits of information > can already be conditional. Let's audit how they were set: > > crypto: always setting can_write_ to false is pointless (the > struct starts life zero-initialized), no use of supported_ > > nbd: just recently fixed to set can_write_ if supported_ > includes MAY_UNMAP (thus this commit effectively reverts > bca80059e and solves the problem mentioned there in a more > global way) > > file-posix, iscsi, qcow2: can_write_ is conditional, while > supported_ was unconditional; but passing MAY_UNMAP would > fail with ENOTSUP if the condition wasn't met > > qed: can_write_ is unconditional, but pwrite_zeroes lacks > support for MAY_UNMAP and supported_ is not set. Perhaps > support can be added later (since it would be similar to > qcow2), but for now claiming false is no real loss > > all other drivers: can_write_ is not set, and supported_ is > either unset or a passthrough > > Simplify the code by moving the conditional into > supported_zero_flags for all drivers, then dropping the > now-unused BDI field. For callers that relied on > bdrv_can_write_zeroes_with_unmap(), we return the same > per-device settings for drivers that had conditions (no > observable change in behavior there); and can now return > true (instead of false) for drivers that support passthrough > (for example, the commit driver) which gives those drivers > the same fix as nbd just got in bca80059e. For callers that > relied on supported_zero_flags, we now have a few more places > that can avoid a wasted call to pwrite_zeroes() that will > just fail with ENOTSUP. > > Suggested-by: Paolo Bonzini <pbonz...@redhat.com> > Signed-off-by: Eric Blake <ebl...@redhat.com> > > --- > The commit id mentioned above is dependent on me not having to respin > my latest NBD pull request: > > Based-on: <20180126160411.4033-1-ebl...@redhat.com> > ([PULL 0/8] NBD patches through 26 Jan) > --- > include/block/block.h | 11 ----------- > block.c | 8 +------- > block/crypto.c | 1 - > block/file-posix.c | 3 +-- > block/iscsi.c | 6 ++++-- > block/nbd.c | 11 ----------- > block/qcow2.c | 3 +-- > block/qed.c | 1 - > 8 files changed, 7 insertions(+), 37 deletions(-)
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
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