scsi-disk: correctly implement WRITE SAME
Fetch the data to be written from the input buffer. If it is all zeroes, we can use the write_zeroes call (possibly with the new MAY_UNMAP flag). Otherwise, do as many write cycles as needed, writing 512k at a time. Strictly speaking, this is still incorrect because a zero cluster should only be written if the MAY_UNMAP flag is set. But this is a bug in qcow2 and the other formats, not in the SCSI code. Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com> Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
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