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error out when run_vminitd.sock path length is too long #89

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error out when run_vminitd.sock path length is too long #89

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9 changes: 9 additions & 0 deletions internal/vm/libkrun/instance.go
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Original file line number Diff line number Diff line change
Expand Up @@ -246,10 +246,19 @@ func (v *vmInstance) Start(ctx context.Context, opts ...vm.StartOpt) (err error)
return fmt.Errorf("failed to get cwd: %w", err)
}
socketPath := filepath.Join(v.state, "run_vminitd.sock")
// Compute the relative socket path to avoid exceeding the max length on macOS.
socketPath, err = filepath.Rel(cwd, socketPath)
if err != nil {
return fmt.Errorf("failed to get relative socket path: %w", err)
}
// When the socket path exceeds macOS max length, it appears as if the VM
// didn't start properly. There's no easy way to figure this out as the
// only log is: "Timeout while waiting for VM to start". Thus, return an
// error preventively here.
if runtime.GOOS == "darwin" && len(socketPath) >= 104 {
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Copilot AI Jan 28, 2026

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The condition checks if length is >= 104, but since the 104-character limit includes the null terminator (\0), the check should be > 103 or >= 104 with the actual path plus null terminator. The current check may reject valid 103-character paths. Consider changing to len(socketPath) > 103 to allow exactly 103 characters of actual path data.

Suggested change
if runtime.GOOS == "darwin" && len(socketPath) >= 104 {
if runtime.GOOS == "darwin" && len(socketPath) > 103 {

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@vvoland vvoland Jan 28, 2026

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I think copilot got confused by your comment:

is limited to 104 characters (including \0).

The limit is 104 bytes (so 103 chars + NUL byte), so the code is correct.

return fmt.Errorf("socket path is too long: %s", socketPath)
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Copilot AI Jan 28, 2026

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The error message should provide actionable guidance. Consider enhancing it to explain the limitation and suggest a solution, such as: socket path exceeds macOS limit of 103 characters (%d): %s. Consider using a shorter state directory path or avoiding symlinked directories in /tmp

Suggested change
return fmt.Errorf("socket path is too long: %s", socketPath)
return fmt.Errorf("socket path exceeds macOS limit of 103 characters (%d): %s. Consider using a shorter state directory path or avoiding symlinked directories in /tmp", len(socketPath), socketPath)

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}

if err := v.vmc.AddVSockPort(1025, socketPath); err != nil {
return fmt.Errorf("failed to add vsock port: %w", err)
}
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