Multiple directory volume mounts fail with RegisterNetDevice(IrqsExhausted) on Linux/libkrun

[fuchencong]

Multiple directory volume mounts fail with RegisterNetDevice(IrqsExhausted) on Linux/libkrun

Summary

Using the official BoxLite CLI directly, a box starts successfully with one or two directory volume mounts, but fails to start with three directory volume mounts.

The failure happens before the command runs inside the guest:

Building the microVM failed: RegisterNetDevice(IrqsExhausted)
VM failed to start (libkrun status=-22)

This was reproduced without any downstream wrapper. The commands below call the official boxlite CLI directly.

Environment

• BoxLite CLI: boxlite 0.9.7
• OS: Ubuntu 22.04.5 LTS
• Kernel: Linux 5.15.0-40-generic x86_64
• Architecture: x86_64
• CPU: AMD EPYC-Milan Processor
• Hypervisor: KVM
• Test image: alpine:3.19

uname -a:

Linux OPS-3430 5.15.0-40-generic #43-Ubuntu SMP Wed Jun 15 12:54:21 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Installation Used for Repro

mkdir -p /tmp/boxlite-bin
BOXLITE_INSTALL_DIR=/tmp/boxlite-bin curl -fsSL https://sh.boxlite.ai | BOXLITE_INSTALL_DIR=/tmp/boxlite-bin sh
/tmp/boxlite-bin/boxlite --version

Output:

boxlite 0.9.7

Reproduction

ROOT=$(mktemp -d /tmp/boxlite-multi-mount-XXXXXX)

for n in 1 2 3 4 5; do
  mkdir -p "$ROOT/dir$n"
  echo "dir$n" > "$ROOT/dir$n/file.txt"
done

for count in 2 3; do
  echo "=== count=$count ==="

  args=()
  checks=""
  for n in $(seq 1 "$count"); do
    args+=("-v" "$ROOT/dir$n:/mnt/dir$n")
    checks="$checks cat /mnt/dir$n/file.txt;"
  done

  BOXLITE_HOME="$ROOT/home-$count" \
  BOXLITE_RUNTIME_DIR=/tmp/boxlite-bin/runtime \
  /tmp/boxlite-bin/boxlite run --rm "${args[@]}" alpine:3.19 sh -lc "$checks"
done

Expected Behavior

Both runs should start the box and print the mounted file contents:

dir1
dir2
dir3

Actual Behavior

Two directory volumes work:

=== count=2 ===
dir1
dir2
[boxlite] Auto-stopping non-detached box: id=qbrbiLGZcQhr, pid=1775403

Three directory volumes fail during VM startup:

=== count=3 ===
Building the microVM failed: RegisterNetDevice(IrqsExhausted)
VM failed to start (libkrun status=-22)

Detailed log excerpt:

[shim] T+19ms: entering VM (krun_start_enter)
[krun] 09:11:57.150665 krun_start_enter called
[2026-07-07T09:11:57.233431Z ERROR krun] Building the microVM failed: RegisterNetDevice(IrqsExhausted)
[krun] 09:11:57.238909 krun_start_enter returned (status=-22, elapsed=88ms)
Error: Engine("VM failed to start (libkrun status=-22)")

Additional Check

Running the same three-volume command with --security disable still fails with the same error:

BOXLITE_HOME="$ROOT/home-security-disabled" \
BOXLITE_RUNTIME_DIR=/tmp/boxlite-bin/runtime \
/tmp/boxlite-bin/boxlite run --rm \
  --security disable \
  -v "$ROOT/dir1:/mnt/dir1" \
  -v "$ROOT/dir2:/mnt/dir2" \
  -v "$ROOT/dir3:/mnt/dir3" \
  alpine:3.19 sh -lc 'cat /mnt/dir1/file.txt; cat /mnt/dir2/file.txt; cat /mnt/dir3/file.txt'

Result:

Building the microVM failed: RegisterNetDevice(IrqsExhausted)
VM failed to start (libkrun status=-22)

Notes

From a quick source read, each user -v/--volume appears to become a distinct virtiofs share. On the Linux x86_64/libkrun path, there are also internal devices such as shared filesystem, block disks, vsock/network, balloon/rng, etc. The failure may be related to the available IRQ/device limit being exhausted when additional virtiofs devices are added.

The visible failure is reported at net device registration, but the trigger seems to be the increased number of volume-backed virtiofs devices.

[DorianZheng]

Hi @fuchencong. Thanks for filing this issue. I will try to reproduce the issue.