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Optimizations for recurrsive unmount

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When a recursive unmount fails, don't bother parsing the mount table to check
if what we expected to be a mountpoint is still mounted. `EINVAL` is
returned when you try to unmount something that is not a mountpoint, the
other cases of `EINVAL` would not apply here unless everything is just
wrong. Parsing the mount table over and over is relatively expensive,
especially in the code path that it's in.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
This commit is contained in:
Brian Goff 2017-08-02 21:29:43 -04:00
parent 92309e34e4
commit dd21087660
1 changed files with 24 additions and 10 deletions
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32
pkg/mount/mount.go
View file

@ -4,6 +4,8 @@ import (
"sort"
"strings"
"syscall"
"github.com/sirupsen/logrus"
)
@ -77,18 +79,30 @@ func RecursiveUnmount(target string) error {
continue
}
logrus.Debugf("Trying to unmount %s", m.Mountpoint)
err = Unmount(m.Mountpoint)
if err != nil && i == len(mounts)-1 {
if mounted, err := Mounted(m.Mountpoint); err != nil || mounted {
err = unmount(m.Mountpoint, mntDetach)
if err != nil {
// If the error is EINVAL either this whole package is wrong (invalid flags passed to unmount(2)) or this is
// not a mountpoint (which is ok in this case).
// Meanwhile calling `Mounted()` is very expensive.
//
// We've purposefully used `syscall.EINVAL` here instead of `unix.EINVAL` to avoid platform branching
// Since `EINVAL` is defined for both Windows and Linux in the `syscall` package (and other platforms),
// this is nicer than defining a custom value that we can refer to in each platform file.
if err == syscall.EINVAL {
continue
}
if i == len(mounts)-1 {
if mounted, e := Mounted(m.Mountpoint); e != nil || mounted {
return err
}
// Ignore errors for submounts and continue trying to unmount others
// The final unmount should fail if there ane any submounts remaining
} else if err != nil {
logrus.Errorf("Failed to unmount %s: %v", m.Mountpoint, err)
} else if err == nil {
logrus.Debugf("Unmounted %s", m.Mountpoint)
continue
}
// This is some submount, we can ignore this error for now, the final unmount will fail if this is a real problem
logrus.WithError(err).Warnf("Failed to unmount submount %s", m.Mountpoint)
continue
}
logrus.Debugf("Unmounted %s", m.Mountpoint)
}
return nil
}