Re: [PATCH 2/2] 9pfs: fix init_in_iov_from_pdu truncating size

[Stefano Stabellini]

On Thu, 14 May 2020, Christian Schoenebeck wrote:
> Looks like this issue will still take quite some time to be fixed with Xen. 
> If 
> you don't mind I'll send out a patch to revert truncation on virtio side, so 
> that at least this bug is fixed with virtio ASAP.

Let me answer to this quickly so that if you want to get the patch out
today you can.


Yes, I think it is OK to revert truncation in virtio now. Only one
thing: would there still be any value in doing for Xen:

+    if (pdu->id + 1 == P9_RREAD) {
+        /* size[4] Rread tag[2] count[4] data[count] */
+        const size_t hdr_size = 11;
+        /*
+         * If current transport buffer size is smaller than actually required
+         * for this Rreaddir response, then truncate the response to the
+         * currently available transport buffer size, however only if it would
+         * at least allow to return 1 payload byte to client.
+         */
+        if (buf_size < hdr_size + 1) {


like your patch here does? Although not a complete solution it looks
like it would still be a good improvement over the current situation for
Xen.