Bug 987278
| Summary: | fail to transfer any data between host and guest with virtio serial through UDP option | ||
|---|---|---|---|
| Product: | Red Hat Enterprise Linux 7 | Reporter: | Sibiao Luo <sluo> |
| Component: | qemu-kvm | Assignee: | Amit Shah <amit.shah> |
| Status: | CLOSED WORKSFORME | QA Contact: | Virtualization Bugs <virt-bugs> |
| Severity: | medium | Docs Contact: | |
| Priority: | medium | ||
| Version: | 7.0 | CC: | acathrow, amit.shah, bsarathy, chayang, flang, hhuang, juzhang, kraxel, mdeng, michen, mkenneth, qzhang, rhod, virt-maint, xfu |
| Target Milestone: | rc | ||
| Target Release: | --- | ||
| Hardware: | Unspecified | ||
| OS: | Unspecified | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | Bug Fix | |
| Doc Text: | Story Points: | --- | |
| Clone Of: | 985214 | Environment: | |
| Last Closed: | 2013-11-26 14:34:47 UTC | Type: | Bug |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
| Bug Depends On: | 985214, 1121579, 1174102 | ||
| Bug Blocks: | |||
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Comment 1
Sibiao Luo
2013-07-23 07:09:42 UTC
udp chardev works for me.
Terminal #1:
nc -4 -u -l 12345
Terminal #2:
qemu-kvm -chardev udp,id=test,port=12345,localport=54321,ipv4 \
-device isa-debugcon,iobase=0x402,chardev=test
seabios log messages show up in Terminal #1 just fine.
Now and then there is a piece missing. But note that unlike TCP the UDP protocol doesn't make any guaranties whatsoever. In case buffers are full packets are simply dropped and lost. So this is normal behavior. Packets can also be reordered.
Note that both qemu+netcat are forced into ipv4 mode to make sure they speak the same protocol.
Also note that I'm explicitly setting localport to avoid a random port being picked. This allows to keep netcat in terminal #1 running while starting qemu multiple times even though netcat will only accept packets from a single peer address.
Final note: The UDP protocol is stateless. There is no "connected" and "disconnected" state. Consequently the UDP chardev backend doesn't send open/close chardev events. Which virtio-serial might depend on to work correctly. Amit?
Bottom line: Testing the udp chardev with anything which requires a reliable stream is bogus in the first place. The only remotely useful use case for the udp chardev backend I can think of is to send guest output to a remote syslog server (which traditionally listens on udp port 514).
(In reply to Gerd Hoffmann from comment #3) > Bottom line: Testing the udp chardev with anything which requires a > reliable stream is bogus in the first place. The only remotely useful use > case for the udp chardev backend I can think of is to send guest output to a > remote syslog server (which traditionally listens on udp port 514). I think that the right test is to validate that data is received. If some/many of the packets are lost, this is OK, as long as many packets are also received. (In reply to Gerd Hoffmann from comment #3) > Final note: The UDP protocol is stateless. There is no "connected" and > "disconnected" state. Consequently the UDP chardev backend doesn't send > open/close chardev events. Which virtio-serial might depend on to work > correctly. Amit? Yep, good point. |