On Mon 12 Mar 2018 11:16:53 AM CET, Anton Nefedov wrote: > The flag is supposed to indicate that the region of the disk image has > to be sufficiently allocated so it reads as zeroes. > > The call with the flag set must return -ENOTSUP if allocation cannot > be done efficiently. > This has to be made sure of by both > - the drivers that support the flag > - and the common block layer (so it will not fall back to any slowpath > (like writing zero buffers) in case the driver does not support > the flag). > > Signed-off-by: Anton Nefedov <anton.nefe...@virtuozzo.com> > Reviewed-by: Eric Blake <ebl...@redhat.com> > Reviewed-by: Alberto Garcia <be...@igalia.com>
Hmm... this is not the patch that I reviewed, please remove the R-b lines when you submit a modified patch. > + /* The BDRV_REQ_ALLOCATE flag is used to indicate that the driver has to > + * efficiently allocate the space so it reads as zeroes, or return an > error. > + * Must be used together with BDRV_REQ_ZERO_WRITE. I guess it's understandable from the context but it's not immediately obvious that you can set BDRV_REQ_ZERO_WRITE but not this one. Perhaps it could be rephrased as something like "If this is set then BDRV_REQ_ZERO_WRITE must also be set". > + * Contradictory to BDRV_REQ_MAY_UNMAP so the two must not be used > together. Or simply "This flag cannot be set together with BDRV_REQ_MAY_UNMAP". > + */ > + BDRV_REQ_ALLOCATE = 0x40, Berto
