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[Bug 1916344] Re: User mode networking not working properly on QEMU on M

From: Adam Chappell
Subject: [Bug 1916344] Re: User mode networking not working properly on QEMU on Mac OS X host
Date: Thu, 25 Feb 2021 17:29:55 -0000

Different problem here I think John. If you run the following you should
the user mode networking that involves Slirp and has the problem.

 qemu-system-i386 -m 700 -hda <Windows XP HD file> -net user -net nic

It's worth noting however that the problem most regularly manifest
itself when a remote server delivers content and THEN closes the TCP
socket straight away. When this happens, the return from the Mac's
poll() system call seems to tickle Slirp's TCP urgent code, which
results in the guest breaking up the received payload, mistakenly
believing some of it to be "urgent". (I've no clue if Windows XP
supports something SO_OOBINLINE that might alleviate the problem...)

If you use HTTP/1.1, you might not see this if the HTTP client is using
a persistent connection, because the server will not close immediately
after transmitting. Not sure what podman does in the opening comment
above, and not sure what IE's default mode of operation is either.

If you're looking for a fix, there is Chris's patch in

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  User mode networking not working properly on QEMU on Mac OS X host

Status in QEMU:

Bug description:
  Steps to reproduce:

  1. Install QEMU using homebrew on Mac OS X (I tried on Catalina and Big Sur)
  2. Spin up a guest VM (say) Cent OS 8 using user mode networking.
  3. Install podman inside the guest
  4. Run podman pull alpine

  The result is:

  [root@localhost ~]# podman pull alpine
  Resolved "alpine" as an alias 
  Trying to pull docker.io/library/alpine:latest...
  Getting image source signatures
  Copying blob ba3557a56b15 [======================================] 2.7MiB / 
    unexpected EOF
  Error: Error writing blob: error storing blob to file 
"/var/tmp/storage851171596/1": error happened during read: unexpected EOF

  This is happening because QEMU is telling the guest that the TCP
  connection is closed even before reading all the data from the host
  socket and forwarding it to the guest.

  This issue doesn't happen on a Linux host. So, that tells me that this
  has something to do with QEMU installation on Mac OS X.

  This could be a slirp related issue. So, QEMU/slirp may need to work
  together on fixing this. Here's the link to the libslirp issue:


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