fix: resolve go vet errors by making fadvise platform-specific

- Split fadviseNotUsed function into platform-specific implementations
  - fadvise_linux.go: Linux-specific implementation using unix.Fadvise
  - fadvise_other.go: No-op implementation for non-Linux platforms
- Remove unused imports (os, path/filepath) from cmd.go
- Remove unix import from cmd.go as it's now only used in Linux-specific file
This resolves the issue where unix.Fadvise and unix.FADV_DONTNEED are not
available on macOS and other non-Linux platforms. The build tags ensure the
correct implementation is compiled for each target OS.

Author: armru

pkg/walarchive/cmd.go

@@ -20,16 +20,13 @@ import (
 	"context"
 	"fmt"
 	"math"
-	"os"
 	"os/exec"
-	"path/filepath"
 	"sync"
 	"time"
 
 	"github.com/cloudnative-pg/machinery/pkg/execlog"
 	"github.com/cloudnative-pg/machinery/pkg/fileutils"
 	"github.com/cloudnative-pg/machinery/pkg/log"
-	"golang.org/x/sys/unix"
 
 	"github.com/cloudnative-pg/barman-cloud/pkg/utils"
 )
@@ -192,30 +189,3 @@ func (archiver *BarmanArchiver) CheckWalArchiveDestination(ctx context.Context,
 
 	return nil
 }
-
-// fadviseNotUsed issues an fadvise to the OS to inform that the file is not needed anymore.
-// This is necessary because we run in a separate container from PostgreSQL in Kubernetes.
-// Without this hint, archived WALs accumulate in page cache since memory pressure on large
-// machines is typically insufficient to evict them, wasting memory that could be used for
-// active workloads. PostgreSQL handles its own cache management, but our archiver sidecar
-// needs to do the same for the files it processes.
-func (archiver *BarmanArchiver) fadviseNotUsed(fileName string) (err error) {
-	file, err := os.Open(filepath.Clean(fileName))
-	if err != nil {
-		return fmt.Errorf("error opening file %s for fadvise: %w", fileName, err)
-	}
-
-	defer func(file *os.File) {
-		closeErr := file.Close()
-		if closeErr != nil && err == nil {
-			err = fmt.Errorf("error closing file %s for fadvise: %w", fileName, closeErr)
-		}
-	}(file)
-
-	fd := int(file.Fd())
-	if fadviseErr := unix.Fadvise(fd, 0, 0, unix.FADV_DONTNEED); fadviseErr != nil {
-		return fmt.Errorf("error issuing fadvise on file %s: %w", fileName, fadviseErr)
-	}
-
-	return nil
-}

pkg/walarchive/fadvise_linux.go

@@ -0,0 +1,54 @@
+//go:build linux
+
+/*
+Copyright The CloudNativePG Contributors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package walarchive
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/sys/unix"
+)
+
+// fadviseNotUsed issues an fadvise to the OS to inform that the file is not needed anymore.
+// This is necessary because we run in a separate container from PostgreSQL in Kubernetes.
+// Without this hint, archived WALs accumulate in page cache since memory pressure on large
+// machines is typically insufficient to evict them, wasting memory that could be used for
+// active workloads. PostgreSQL handles its own cache management, but our archiver sidecar
+// needs to do the same for the files it processes.
+func (archiver *BarmanArchiver) fadviseNotUsed(fileName string) (err error) {
+	file, err := os.Open(filepath.Clean(fileName))
+	if err != nil {
+		return fmt.Errorf("error opening file %s for fadvise: %w", fileName, err)
+	}
+
+	defer func(file *os.File) {
+		closeErr := file.Close()
+		if closeErr != nil && err == nil {
+			err = fmt.Errorf("error closing file %s for fadvise: %w", fileName, closeErr)
+		}
+	}(file)
+
+	fd := int(file.Fd())
+	if fadviseErr := unix.Fadvise(fd, 0, 0, unix.FADV_DONTNEED); fadviseErr != nil {
+		return fmt.Errorf("error issuing fadvise on file %s: %w", fileName, fadviseErr)
+	}
+
+	return nil
+}

pkg/walarchive/fadvise_other.go

@@ -0,0 +1,30 @@
+//go:build !linux
+
+/*
+Copyright The CloudNativePG Contributors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package walarchive
+
+// fadviseNotUsed is a no-op on non-Linux platforms where fadvise is not available.
+// On Linux, this function issues an fadvise to the OS to inform that the file is not needed anymore.
+// This is necessary because we run in a separate container from PostgreSQL in Kubernetes.
+// Without this hint, archived WALs accumulate in page cache since memory pressure on large
+// machines is typically insufficient to evict them, wasting memory that could be used for
+// active workloads. PostgreSQL handles its own cache management, but our archiver sidecar
+// needs to do the same for the files it processes.
+func (archiver *BarmanArchiver) fadviseNotUsed(fileName string) error {
+	return nil
+}