Add a util/mount pkg

doc.go

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+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 mount defines an interface to mounting filesystems.
+package mount

linux.go

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+// +build linux
+
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 mount
+
+import (
+	"bufio"
+	"fmt"
+	"hash/adler32"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+	"syscall"
+
+	"github.com/golang/glog"
+)
+
+const FlagBind = syscall.MS_BIND
+const FlagReadOnly = syscall.MS_RDONLY
+
+type mounter struct{}
+
+// Wraps syscall.Mount()
+func (mounter *mounter) Mount(source string, target string, fstype string, flags uintptr, data string) error {
+	glog.V(5).Infof("Mounting %s %s %s %d %s", source, target, fstype, flags, data)
+	return syscall.Mount(source, target, fstype, flags, data)
+}
+
+// Wraps syscall.Unmount()
+func (mounter *mounter) Unmount(target string, flags int) error {
+	return syscall.Unmount(target, flags)
+}
+
+// How many times to retry for a consistent read of /proc/mounts.
+const maxListTries = 3
+
+func (mounter *mounter) List() ([]MountPoint, error) {
+	hash1, err := readProcMounts(nil)
+	if err != nil {
+		return nil, err
+	}
+
+	for i := 0; i < maxListTries; i++ {
+		mps := []MountPoint{}
+		hash2, err := readProcMounts(&mps)
+		if err != nil {
+			return nil, err
+		}
+		if hash1 == hash2 {
+			// Success
+			return mps, nil
+		}
+		hash1 = hash2
+	}
+	return nil, fmt.Errorf("failed to get a consistent snapshot of /proc/mounts after %d tries", maxListTries)
+}
+
+// As per the fstab man page.
+const expectedNumFieldsPerLine = 6
+
+// Read /proc/mounts and produces a hash of the contents.  If the out argument
+// is not nil, this fills it with MountPoint structs.
+func readProcMounts(out *[]MountPoint) (uint32, error) {
+	file, err := os.Open("/proc/mounts")
+	if err != nil {
+		return 0, err
+	}
+	defer file.Close()
+	return readProcMountsFrom(file, out)
+}
+
+func readProcMountsFrom(file io.Reader, out *[]MountPoint) (uint32, error) {
+	hash := adler32.New()
+	scanner := bufio.NewReader(file)
+	for {
+		line, err := scanner.ReadString('\n')
+		if err == io.EOF {
+			break
+		}
+		fields := strings.Fields(line)
+		if len(fields) != expectedNumFieldsPerLine {
+			return 0, fmt.Errorf("wrong number of fields (expected %d, got %d): %s", expectedNumFieldsPerLine, len(fields), line)
+		}
+
+		fmt.Fprintf(hash, "%s", line)
+
+		if out != nil {
+			mp := MountPoint{
+				Device: fields[0],
+				Path:   fields[1],
+				Type:   fields[2],
+				Opts:   strings.Split(fields[3], ","),
+			}
+
+			freq, err := strconv.Atoi(fields[4])
+			if err != nil {
+				return 0, err
+			}
+			mp.Freq = freq
+
+			pass, err := strconv.Atoi(fields[5])
+			if err != nil {
+				return 0, err
+			}
+			mp.Pass = pass
+
+			*out = append(*out, mp)
+		}
+	}
+	return hash.Sum32(), nil
+}

linux_test.go

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+// +build linux
+
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 mount
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestReadProcMountsFrom(t *testing.T) {
+	successCase :=
+		`/dev/0 /path/to/0 type0 flags 0 0
+		/dev/1    /path/to/1   type1	flags 1 1
+		/dev/2 /path/to/2 type2 flags,1,2=3 2 2
+		`
+	hash, err := readProcMountsFrom(strings.NewReader(successCase), nil)
+	if err != nil {
+		t.Errorf("expected success")
+	}
+	if hash != 0xa3522051 {
+		t.Errorf("expected 0xa3522051, got %#x", hash)
+	}
+	mounts := []MountPoint{}
+	hash, err = readProcMountsFrom(strings.NewReader(successCase), &mounts)
+	if err != nil {
+		t.Errorf("expected success")
+	}
+	if hash != 0xa3522051 {
+		t.Errorf("expected 0xa3522051, got %#x", hash)
+	}
+	if len(mounts) != 3 {
+		t.Fatalf("expected 3 mounts, got %d", len(mounts))
+	}
+	mp := MountPoint{"/dev/0", "/path/to/0", "type0", []string{"flags"}, 0, 0}
+	if !mountPointsEqual(&mounts[0], &mp) {
+		t.Errorf("got unexpected MountPoint[0]: %#v", mounts[0])
+	}
+	mp = MountPoint{"/dev/1", "/path/to/1", "type1", []string{"flags"}, 1, 1}
+	if !mountPointsEqual(&mounts[1], &mp) {
+		t.Errorf("got unexpected MountPoint[1]: %#v", mounts[1])
+	}
+	mp = MountPoint{"/dev/2", "/path/to/2", "type2", []string{"flags", "1", "2=3"}, 2, 2}
+	if !mountPointsEqual(&mounts[2], &mp) {
+		t.Errorf("got unexpected MountPoint[2]: %#v", mounts[2])
+	}
+
+	errorCases := []string{
+		"/dev/0 /path/to/mount\n",
+		"/dev/1 /path/to/mount type flags a 0\n",
+		"/dev/2 /path/to/mount type flags 0 b\n",
+	}
+	for _, ec := range errorCases {
+		_, err := readProcMountsFrom(strings.NewReader(ec), &mounts)
+		if err == nil {
+			t.Errorf("expected error")
+		}
+	}
+}
+
+func mountPointsEqual(a, b *MountPoint) bool {
+	if a.Device != b.Device || a.Path != b.Path || a.Type != b.Type || !slicesEqual(a.Opts, b.Opts) || a.Pass != b.Pass || a.Freq != b.Freq {
+		return false
+	}
+	return true
+}
+
+func slicesEqual(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}

mount.go

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+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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.
+*/
+
+// TODO(thockin): This whole pkg is pretty linux-centric.  As soon as we have
+// an alternate platform, we will need to abstract further.
+package mount
+
+// Each supported platform must define the following flags:
+//   - FlagBind: specifies a bind mount
+//   - FlagReadOnly: the mount will be read-only
+type Interface interface {
+	// Mount wraps syscall.Mount().
+	Mount(source string, target string, fstype string, flags uintptr, data string) error
+
+	// Umount wraps syscall.Mount().
+	Unmount(target string, flags int) error
+
+	// List returns a list of all mounted filesystems.  This can be large.
+	// On some platforms, reading mounts is not guaranteed consistent (i.e.
+	// it could change between chunked reads). This is guaranteed to be
+	// consistent.
+	List() ([]MountPoint, error)
+}
+
+// New returns a mount.Interface for the current system.
+func New() Interface {
+	return &mounter{}
+}
+
+// This represents a single line in /proc/mounts or /etc/fstab.
+type MountPoint struct {
+	Device string
+	Path   string
+	Type   string
+	Opts   []string
+	Freq   int
+	Pass   int
+}

unsupported.go

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+// +build !linux
+
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 mount
+
+const FlagBind = 0
+const FlagReadOnly = 0
+
+type mounter struct{}
+
+func (mounter *mounter) Mount(source string, target string, fstype string, flags uintptr, data string) error {
+	return nil
+}
+
+func (mounter *mounter) Unmount(target string, flags int) error {
+	return nil
+}
+
+func (mounter *mounter) List() ([]MountPoint, error) {
+	return []MountPoint{}, nil
+}