unixgram: Make fd non-blocking by jakecorrenti · Pull Request #402 · containers/libkrun

jakecorrenti · 2025-08-30T01:26:44Z

When creating unixgram backend from existing fd we need to make it non-blocking so the user does not have to care about this implementation detail. Disabling SIGPIPE is needed on the existing fd for the same reason.

Fix by moving these steps from open() to new().

Authored-by: Nir Soffer nirsof@gmail.com

nirs · 2025-08-30T17:05:57Z

-            send(fd, &VFKIT_MAGIC, MsgFlags::empty()).map_err(ConnectError::SendingMagic)?;
-        }
-
        // macOS forces us to do this here instead of just using SockFlag::SOCK_NONBLOCK above.


This comment was good in open() since we created the socket above. In new() we need another comment explaining that we handle socket from 2 sources - user socket and socket created in open. The comment in my patch tried to explain this by maybe it should be improved:

// For existing socket we must make the socket non-blocking here. When // opening the socket we can create it non-blocking but not on macOS.

I've opted for simplifying the comment, since in that context doesn't make sense to talk about macOS.

nirs · 2025-08-30T17:43:37Z

@jakecorrenti added issue #403

nirs · 2025-08-30T17:53:27Z

Tests, this fixes the issue:

Using krunkit PR adding unixgram device:
libkrun/krunkit#63

And vmnet-helper PR for supporting unixgram device:
nirs/vmnet-helper#92

VM using fd=

% ./example server --driver krunkit --connection fd
Starting vmnet-helper for 'server' with interface id 'bdc7b3e0-8594-4814-aa25-05187ad2a36e'
Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/server/cidata.iso'
Starting 'krunkit' virtual machine 'server' with mac address '92:c9:52:b7:6c:08'
Virtual machine IP address: 192.168.105.2

The krunkit command:

% ps | grep krunkit | grep fd=                     
 4769 ttys007    0:04.34 krunkit --memory=1024 --cpus=1 --restful-uri=none:// --device=virtio-blk,path=/Users/nir/.vmnet-helper/vms/server/disk.img --device=virtio-blk,path=/Users/nir/.vmnet-helper/vms/server/cidata.iso --device=virtio-serial,logFilePath=/Users/nir/.vmnet-helper/vms/server/serial.log --krun-log-level=3 --device=virtio-net,type=unixgram,fd=3,mac=92:c9:52:b7:6c:08,offloading=off

iperf3 run:

% iperf3 -c 192.168.105.2   
Connecting to host 192.168.105.2, port 5201
[  5] local 192.168.105.1 port 55110 connected to 192.168.105.2 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.01   sec  1.04 GBytes  8.92 Gbits/sec                  
[  5]   1.01-2.01   sec  1.06 GBytes  9.09 Gbits/sec                  
[  5]   2.01-3.01   sec  1.06 GBytes  9.10 Gbits/sec                  
[  5]   3.01-4.01   sec  1.05 GBytes  9.01 Gbits/sec                  
[  5]   4.01-5.01   sec  1.05 GBytes  9.06 Gbits/sec                  
[  5]   5.01-6.01   sec  1.05 GBytes  8.99 Gbits/sec                  
[  5]   6.01-7.01   sec  1.06 GBytes  9.12 Gbits/sec                  
[  5]   7.01-8.01   sec  1.05 GBytes  9.06 Gbits/sec                  
[  5]   8.01-9.01   sec  1.05 GBytes  9.05 Gbits/sec                  
[  5]   9.01-10.01  sec  1.05 GBytes  9.04 Gbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-10.01  sec  10.5 GBytes  9.04 Gbits/sec                  sender
[  5]   0.00-10.01  sec  10.5 GBytes  9.04 Gbits/sec                  receiver

VM using path=

% ./example server --driver krunkit --connection socket
Starting vmnet-helper for 'server' with interface id 'bdc7b3e0-8594-4814-aa25-05187ad2a36e'
Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/server/cidata.iso'
Starting 'krunkit' virtual machine 'server' with mac address '92:c9:52:b7:6c:08'
Virtual machine IP address: 192.168.105.2

% ps | grep krunkit | grep path=  
 4798 ttys007    0:03.20 krunkit --memory=1024 --cpus=1 --restful-uri=none:// --device=virtio-blk,path=/Users/nir/.vmnet-helper/vms/server/disk.img --device=virtio-blk,path=/Users/nir/.vmnet-helper/vms/server/cidata.iso --device=virtio-serial,logFilePath=/Users/nir/.vmnet-helper/vms/server/serial.log --krun-log-level=3 --device=virtio-net,type=unixgram,path=/Users/nir/.vmnet-helper/vms/server/vmnet.sock,mac=92:c9:52:b7:6c:08,offloading=off

iperf3 run:

% iperf3 -c 192.168.105.2
Connecting to host 192.168.105.2, port 5201
[  5] local 192.168.105.1 port 55117 connected to 192.168.105.2 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  1.03 GBytes  8.78 Gbits/sec                  
[  5]   1.00-2.01   sec  1.05 GBytes  9.00 Gbits/sec                  
[  5]   2.01-3.01   sec  1.03 GBytes  8.84 Gbits/sec                  
[  5]   3.01-4.01   sec  1.05 GBytes  8.99 Gbits/sec                  
[  5]   4.01-5.00   sec  1.05 GBytes  9.05 Gbits/sec                  
[  5]   5.00-6.00   sec  1.06 GBytes  9.12 Gbits/sec                  
[  5]   6.00-7.01   sec  1.05 GBytes  9.01 Gbits/sec                  
[  5]   7.01-8.00   sec  1.05 GBytes  8.99 Gbits/sec                  
[  5]   8.00-9.00   sec  1.06 GBytes  9.08 Gbits/sec                  
[  5]   9.00-10.00  sec  1.05 GBytes  9.04 Gbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-10.00  sec  10.5 GBytes  8.99 Gbits/sec                  sender
[  5]   0.00-10.00  sec  10.5 GBytes  8.99 Gbits/sec                  receiver

nirs

The comments can be improved later.

Latest krunkit can use a file descriptor instead of unix socket. Update the krunkit command to support this. Since krunkit behaves like vfkit and qemu, we can remove the special "auto" connection. Depends on: - libkrun/krunkit#63 - containers/libkrun#402

Previously we use "auto", "on", "off" to enable offloading automatically for krunkit since it was always required. Now that this is an optional features we can simplify to boolean flag. Depends on: - libkrun/krunkit#63 - containers/libkrun#402

slp · 2025-09-01T07:45:45Z

The comment for krun_add_net_unixgram in libkrun.h states that:

If using "fd", the socket must be already initialized and configured as the userspace network proxy requires.

In my head, that also meant library users would need to configure the socket as non-blocking before calling the function. But it's true that, strictly speaking, making it non-blocking is our requirement, not the userspace network proxy requirement, so I guess it's reasonable doing this ourselves...

About this PR in particular, we need to make it non-blocking on both new and open, as otherwise we're fixing one but breaking the other.

slp · 2025-09-01T07:53:54Z

About this PR in particular, we need to make it non-blocking on both new and open, as otherwise we're fixing one but breaking the other.

Correcting myself, open ends calling new, so this should work just fine.

When creating unixgram backend from existing fd we need to make it non-blocking so the user does not have to care about this implementation detail. Disabling SIGPIPE is needed on the existing fd for the same reason. Fix by moving these steps from open() to new(). Authored-by: Nir Soffer <nirsof@gmail.com> Signed-off-by: Nir Soffer <nirsof@gmail.com> Signed-off-by: Jake Correnti <jakecorrenti+github@proton.me> Signed-off-by: Sergio Lopez <slp@redhat.com>

slp

LGTM, thanks @nirs and @jakecorrenti

Set up the stage for a quick bug-fix release including a patch fixing network configuration with unixgram sockets (containers#402). Signed-off-by: Sergio Lopez <slp@redhat.com>

Set up the stage for a quick bug-fix release including a patch fixing network configuration with unixgram sockets (#402). Signed-off-by: Sergio Lopez <slp@redhat.com>

Latest krunkit can use a file descriptor instead of unix socket. Update the krunkit command to support this. Since krunkit behaves like vfkit and qemu, we can remove the special "auto" connection. Depends on: - libkrun/krunkit#63 - containers/libkrun#402

Previously we use "auto", "on", "off" to enable offloading automatically for krunkit since it was always required. Now that this is an optional features we can simplify to boolean flag. Depends on: - libkrun/krunkit#63 - containers/libkrun#402

Set up the stage for a quick bug-fix release including a patch fixing network configuration with unixgram sockets (containers#402). Signed-off-by: Sergio Lopez <slp@redhat.com>

nirs reviewed Aug 30, 2025

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nirs mentioned this pull request Aug 30, 2025

Add --device virtio-net,type=unix{gram,stream} libkrun/krunkit#63

Merged

nirs approved these changes Aug 30, 2025

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nirs mentioned this pull request Aug 31, 2025

Support krunkit new virtio-net unixgram options nirs/vmnet-helper#92

Merged

jakecorrenti marked this pull request as ready for review September 1, 2025 02:26

jakecorrenti requested review from MatiasVara, mtjhrc, slp and tylerfanelli as code owners September 1, 2025 02:26

jakecorrenti changed the title ~~WIP: unixgram: Make fd non-blocking~~ unixgram: Make fd non-blocking Sep 1, 2025

slp force-pushed the fix-unixgram branch from 58e279f to 6b1ede9 Compare September 1, 2025 08:00

slp force-pushed the fix-unixgram branch from 6b1ede9 to 7ab73dc Compare September 1, 2025 08:02

slp approved these changes Sep 1, 2025

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slp merged commit f617f3d into containers:main Sep 1, 2025
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slp added a commit to slp/libkrun that referenced this pull request Sep 1, 2025

Bump version to 1.15.1

968d971

Set up the stage for a quick bug-fix release including a patch fixing network configuration with unixgram sockets (containers#402). Signed-off-by: Sergio Lopez <slp@redhat.com>

This was referenced Sep 1, 2025

Bump version to 1.15.1 #404

Merged

krun_add_net_unixgram broken when using fd #403

Closed

slp added a commit that referenced this pull request Sep 1, 2025

Bump version to 1.15.1

d3e1755

Set up the stage for a quick bug-fix release including a patch fixing network configuration with unixgram sockets (#402). Signed-off-by: Sergio Lopez <slp@redhat.com>

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VM using fd=

VM using path=

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