Add qvm doctor command to diagnose and fix common issues

internal/lock/lock.go

@@ -0,0 +1,78 @@
+// Package lock provides file-based locking for VM operations.
+package lock
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+	"time"
+
+	"github.com/samber/mo"
+	"qvm/internal/config"
+)
+
+// Lock represents an exclusive file lock on VM operations.
+type Lock struct {
+	file *os.File
+}
+
+var lockPath = filepath.Join(config.StateDir, "vm.lock")
+
+// Acquire obtains an exclusive lock on VM operations.
+// Blocks until the lock is available or timeout is reached.
+func Acquire(timeout time.Duration) mo.Result[*Lock] {
+	if err := os.MkdirAll(config.StateDir, 0755); err != nil {
+		return mo.Err[*Lock](fmt.Errorf("failed to create state directory: %w", err))
+	}
+
+	file, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0644)
+	if err != nil {
+		return mo.Err[*Lock](fmt.Errorf("failed to open lock file: %w", err))
+	}
+
+	deadline := time.Now().Add(timeout)
+	for {
+		err := syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
+		if err == nil {
+			return mo.Ok(&Lock{file: file})
+		}
+
+		if time.Now().After(deadline) {
+			file.Close()
+			return mo.Err[*Lock](fmt.Errorf("timeout waiting for VM lock after %v", timeout))
+		}
+
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+// TryAcquire attempts to obtain an exclusive lock without blocking.
+// Returns error if lock is held by another process.
+func TryAcquire() mo.Result[*Lock] {
+	if err := os.MkdirAll(config.StateDir, 0755); err != nil {
+		return mo.Err[*Lock](fmt.Errorf("failed to create state directory: %w", err))
+	}
+
+	file, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0644)
+	if err != nil {
+		return mo.Err[*Lock](fmt.Errorf("failed to open lock file: %w", err))
+	}
+
+	err = syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
+	if err != nil {
+		file.Close()
+		return mo.Err[*Lock](fmt.Errorf("VM operation in progress by another process"))
+	}
+
+	return mo.Ok(&Lock{file: file})
+}
+
+// Release releases the lock.
+func (l *Lock) Release() error {
+	if l.file == nil {
+		return nil
+	}
+	syscall.Flock(int(l.file.Fd()), syscall.LOCK_UN)
+	return l.file.Close()
+}