On 2021/7/29 14:28, Viresh Kumar wrote:
On 29-07-21, 14:18, Jie Deng wrote:
The number of descriptors required for a request will not be fixed.
That is true today as well, as we allow 3 (write or read) or 4
(write-read) descriptors.
If there is a descriptor sequence in the virtqueue, then you may need a
state machine
to parse the sequence. For example, when you have
WR RR ZR
O O I O I I O I
* WR:(write request), RR (read request), ZR (zero request), O: output
descriptor, I: input descriptor
When you encounter "O I" combination, you have to read the element after it
to distinguish
RR and ZR. Will this bring unnecessary difficulties for the backend coding ?
I understand what you are saying, but at least all the backends that I
have worked with (Qemu and Rust), further categorizes these into
blocks and this is how it looks there (writing in qemu terminology):
VuVirtqElement *elem = vu_queue_pop();
elem->in_num and elem_out_num gives the number of out/in buffers
there.
And so there is no way one can get confused between two different
elements and you will always know if it is WR or RR or ZR.
Then it's good. Thank you.
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