multibuffer in packed queue

Hellow, I've got question about chapter 2.7.9:

 2.7.9 Multi-buffer requests
Some devices combine multiple buffers as part of processing of a single request. These devices always
mark the descriptor corresponding to the first buffer in the request used after the rest of the descriptors
(corresponding to rest of the buffers) in the request - which follow the first descriptor in ring order - has been
marked used and written out into the ring. This guarantees that the driver will never observe a partial request
in the ring.ÂÂ

Does it mean, that device can use sequence(chain) of descriptor unil descriptor with VIRTQ_DESC_F_NEXTÂ == 0 bit is found, OR device can use descriptors as many as it needs, don't care aboutÂ

VIRTQ_DESC_F_NEXT bit, and finally setÂ

VIRTQ_DESC_F_NEXT bit in all used descriptors.

Also, in packed queue device can't modify descriptors except USED bit. In split queue, device also can't modify descriptor(it touches used buffer with index and length fields). Is that true?

Thank You