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mount: handle loopback mount

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If a mount has specified `loop` option, we need to handle it on our
own instead of passing it to the kernel. In such case, create a
loopback device, attach the mount source to it, and mount the loopback
device rather than the mount source.

Signed-off-by: Peng Tao <bergwolf@hyper.sh>
This commit is contained in:
Peng Tao
2020-03-13 14:40:58 +08:00
committed by Maksym Pavlenko
parent 602af6f677
commit 9e42070169
3 changed files with 370 additions and 7 deletions
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30
mount/mount_linux.go
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@@ -42,7 +42,7 @@ func init() {
//
// If m.Type starts with "fuse." or "fuse3.", "mount.fuse" or "mount.fuse3"
// helper binary is called.
func (m *Mount) Mount(target string) error {
func (m *Mount) Mount(target string) (err error) {
for _, helperBinary := range allowedHelperBinaries {
// helperBinary = "mount.fuse", typePrefix = "fuse."
typePrefix := strings.TrimPrefix(helperBinary, "mount.") + "."
@@ -62,7 +62,7 @@ func (m *Mount) Mount(target string) error {
chdir, options = compactLowerdirOption(options)
}
flags, data := parseMountOptions(options)
flags, data, losetup := parseMountOptions(options)
if len(data) > pagesize {
return errors.Errorf("mount options is too long")
}
@@ -77,7 +77,19 @@ func (m *Mount) Mount(target string) error {
if flags&unix.MS_REMOUNT == 0 || data != "" {
// Initial call applying all non-propagation flags for mount
// or remount with changed data
if err := mountAt(chdir, m.Source, target, m.Type, uintptr(oflags), data); err != nil {
source := m.Source
if losetup {
devFile, err := setupLoop(m.Source, LoopParams{
Readonly: oflags&unix.MS_RDONLY == unix.MS_RDONLY,
Autoclear: true})
if err != nil {
return err
}
defer devFile.Close()
// Mount the loop device instead
source = devFile.Name()
}
if err := mountAt(chdir, source, target, m.Type, uintptr(oflags), data); err != nil {
return err
}
}
@@ -186,11 +198,13 @@ func UnmountAll(mount string, flags int) error {
// parseMountOptions takes fstab style mount options and parses them for
// use with a standard mount() syscall
func parseMountOptions(options []string) (int, string) {
func parseMountOptions(options []string) (int, string, bool) {
var (
flag int
data []string
flag int
losetup bool
data []string
)
loopOpt := "loop"
flags := map[string]struct {
clear bool
flag int
@@ -231,11 +245,13 @@ func parseMountOptions(options []string) (int, string) {
} else {
flag |= f.flag
}
} else if o == loopOpt {
losetup = true
} else {
data = append(data, o)
}
}
return flag, strings.Join(data, ",")
return flag, strings.Join(data, ","), losetup
}
// compactLowerdirOption updates overlay lowdir option and returns the common