From: Frantisek Sumsal <frantisek@sumsal.cz>
Date: Sat, 27 Jun 2026 17:08:06 +0000 (+0200)
Subject: vmspawn: complain loudly if we can't prepare a unix socket for virtiofsd
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7804fd182c3be53303387cd14b68d9bca7378d17;p=thirdparty%2Fsystemd.git

vmspawn: complain loudly if we can't prepare a unix socket for virtiofsd

I couldn't convince vmspawn to start a VM on a Fedora image I just
downloaded, and it was pretty light on any useful details:

$ build/systemd-vmspawn --image ~/Downloads/Fedora-Server-Guest-Generic-Rawhide-20260627.n.0.x86_64.qcow2 --image-format=qcow2 --bind-ro=/tmp/bar; echo $?
░ Spawning VM Fedora-Server-Guest-Generic-Rawhide-20260627.n.0.x8664.qcow2 on /home/mrc0mmand/Downloads/Fedora-Server-Guest-Generic-Rawhide-20260627.n.0.x86_64.qcow2.
░ Press Ctrl-] three times within 1s to kill VM.
1

Turns out that the unix socket path vmspawn generates for the virtiofsd
socket is too long. Let's relay this information to the user as well to
make debugging this a little less painful:

$ build/systemd-vmspawn --image ~/Downloads/Fedora-Server-Guest-Generic-Rawhide-20260627.n.0.x86_64.qcow2 --image-format=qcow2 --bind-ro=/tmp/bar
░ Spawning VM Fedora-Server-Guest-Generic-Rawhide-20260627.n.0.x8664.qcow2 on /home/mrc0mmand/Downloads/Fedora-Server-Guest-Generic-Rawhide-20260627.n.0.x86_64.qcow2.
░ Press Ctrl-] three times within 1s to kill VM.
Failed to prepare unix socket '/run/user/1000/systemd/vmspawn/Fedora-Server-Guest-Generic-Rawhide-20260627.n.0.x8664.qcow2/sock-9594581dcf598992': File name too long
---

diff --git a/src/vmspawn/vmspawn.c b/src/vmspawn/vmspawn.c
index b8d42c55873..6e2329f7f9c 100644
--- a/src/vmspawn/vmspawn.c
+++ b/src/vmspawn/vmspawn.c
@@ -1719,7 +1719,7 @@ static int start_virtiofsd(
         union sockaddr_union su;
         r = sockaddr_un_set_path(&su.un, listen_address);
         if (r < 0)
-                return r;
+                return log_error_errno(r, "Failed to prepare unix socket '%s': %m", listen_address);
 
         _cleanup_close_ int sock = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
         if (sock < 0)