github.com/docker/docker@v299999999.0.0-20200612211812-aaf470eca7b5+incompatible/daemon/graphdriver/devmapper/mount.go (about)

     1  // +build linux
     2  
     3  package devmapper // import "github.com/docker/docker/daemon/graphdriver/devmapper"
     4  
     5  import (
     6  	"bytes"
     7  	"fmt"
     8  	"os"
     9  )
    10  
    11  type probeData struct {
    12  	fsName string
    13  	magic  string
    14  	offset uint64
    15  }
    16  
    17  // ProbeFsType returns the filesystem name for the given device id.
    18  func ProbeFsType(device string) (string, error) {
    19  	probes := []probeData{
    20  		{"btrfs", "_BHRfS_M", 0x10040},
    21  		{"ext4", "\123\357", 0x438},
    22  		{"xfs", "XFSB", 0},
    23  	}
    24  
    25  	maxLen := uint64(0)
    26  	for _, p := range probes {
    27  		l := p.offset + uint64(len(p.magic))
    28  		if l > maxLen {
    29  			maxLen = l
    30  		}
    31  	}
    32  
    33  	file, err := os.Open(device)
    34  	if err != nil {
    35  		return "", err
    36  	}
    37  	defer file.Close()
    38  
    39  	buffer := make([]byte, maxLen)
    40  	l, err := file.Read(buffer)
    41  	if err != nil {
    42  		return "", err
    43  	}
    44  
    45  	if uint64(l) != maxLen {
    46  		return "", fmt.Errorf("devmapper: unable to detect filesystem type of %s, short read", device)
    47  	}
    48  
    49  	for _, p := range probes {
    50  		if bytes.Equal([]byte(p.magic), buffer[p.offset:p.offset+uint64(len(p.magic))]) {
    51  			return p.fsName, nil
    52  		}
    53  	}
    54  
    55  	return "", fmt.Errorf("devmapper: Unknown filesystem type on %s", device)
    56  }
    57  
    58  func joinMountOptions(a, b string) string {
    59  	if a == "" {
    60  		return b
    61  	}
    62  	if b == "" {
    63  		return a
    64  	}
    65  	return a + "," + b
    66  }