On 04/21/2018 08:29 AM, Max Reitz wrote: > This flag signifies that a write request will not change the visible > disk content. With this flag set, it is sufficient to have the > BLK_PERM_WRITE_UNCHANGED permission instead of BLK_PERM_WRITE. > > Signed-off-by: Max Reitz <mre...@redhat.com> > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com> > Reviewed-by: Alberto Garcia <be...@igalia.com> > --- > include/block/block.h | 6 +++++- > block/io.c | 6 +++++- > 2 files changed, 10 insertions(+), 2 deletions(-)
Since patch 5 adds an instance of a driver setting supported_write_flags = BDRV_REQ_WRITE_UNCHANGED, I think this patch should tweak the documentation of supported_write_flags (and supported_zero_flags?) in block_int.h to mention that drivers can opt-in to supporting this particular flag (rather than it being handled completely at the block layer). Also, that does raise the question of whether you have more work to support write-zero requests with WRITE_UNCHANGED (which indeed sounds like something plausible to support). -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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