pinning.go

Documentation: github.com/cilium/ebpf/internal

     1  package internal
     2  
     3  import (
     4  	"errors"
     5  	"fmt"
     6  	"os"
     7  	"path/filepath"
     8  	"runtime"
     9  	"unsafe"
    10  
    11  	"github.com/cilium/ebpf/internal/sys"
    12  	"github.com/cilium/ebpf/internal/unix"
    13  )
    14  
    15  func Pin(currentPath, newPath string, fd *sys.FD) error {
    16  	const bpfFSType = 0xcafe4a11
    17  
    18  	if newPath == "" {
    19  		return errors.New("given pinning path cannot be empty")
    20  	}
    21  	if currentPath == newPath {
    22  		return nil
    23  	}
    24  
    25  	var statfs unix.Statfs_t
    26  	if err := unix.Statfs(filepath.Dir(newPath), &statfs); err != nil {
    27  		return err
    28  	}
    29  
    30  	fsType := int64(statfs.Type)
    31  	if unsafe.Sizeof(statfs.Type) == 4 {
    32  		// We're on a 32 bit arch, where statfs.Type is int32. bpfFSType is a
    33  		// negative number when interpreted as int32 so we need to cast via
    34  		// uint32 to avoid sign extension.
    35  		fsType = int64(uint32(statfs.Type))
    36  	}
    37  
    38  	if fsType != bpfFSType {
    39  		return fmt.Errorf("%s is not on a bpf filesystem", newPath)
    40  	}
    41  
    42  	defer runtime.KeepAlive(fd)
    43  
    44  	if currentPath == "" {
    45  		return sys.ObjPin(&sys.ObjPinAttr{
    46  			Pathname: sys.NewStringPointer(newPath),
    47  			BpfFd:    fd.Uint(),
    48  		})
    49  	}
    50  
    51  	// Renameat2 is used instead of os.Rename to disallow the new path replacing
    52  	// an existing path.
    53  	err := unix.Renameat2(unix.AT_FDCWD, currentPath, unix.AT_FDCWD, newPath, unix.RENAME_NOREPLACE)
    54  	if err == nil {
    55  		// Object is now moved to the new pinning path.
    56  		return nil
    57  	}
    58  	if !os.IsNotExist(err) {
    59  		return fmt.Errorf("unable to move pinned object to new path %v: %w", newPath, err)
    60  	}
    61  	// Internal state not in sync with the file system so let's fix it.
    62  	return sys.ObjPin(&sys.ObjPinAttr{
    63  		Pathname: sys.NewStringPointer(newPath),
    64  		BpfFd:    fd.Uint(),
    65  	})
    66  }
    67  
    68  func Unpin(pinnedPath string) error {
    69  	if pinnedPath == "" {
    70  		return nil
    71  	}
    72  	err := os.Remove(pinnedPath)
    73  	if err == nil || os.IsNotExist(err) {
    74  		return nil
    75  	}
    76  	return err
    77  }
    78
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