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@@ -7,6 +7,34 @@ import (
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"golang.org/x/sys/unix"
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)
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+// MountedFast is a method of detecting a mount point without reading
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+// mountinfo from procfs. A caller can only trust the result if no error
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+// and sure == true are returned. Otherwise, other methods (e.g. parsing
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+// /proc/mounts) have to be used. If unsure, use Mounted instead (which
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+// uses MountedFast, but falls back to parsing mountinfo if needed).
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+//
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+// If a non-existent path is specified, an appropriate error is returned.
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+// In case the caller is not interested in this particular error, it should
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+// be handled separately using e.g. errors.Is(err, os.ErrNotExist).
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+//
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+// This function is only available on Linux. When available (since kernel
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+// v5.6), openat2(2) syscall is used to reliably detect all mounts. Otherwise,
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+// the implementation falls back to using stat(2), which can reliably detect
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+// normal (but not bind) mounts.
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+func MountedFast(path string) (mounted, sure bool, err error) {
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+ // Root is always mounted.
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+ if path == string(os.PathSeparator) {
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+ return true, true, nil
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+ }
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+
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+ path, err = normalizePath(path)
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+ if err != nil {
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+ return false, false, err
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+ }
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+ mounted, sure, err = mountedFast(path)
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+ return
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+}
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+
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// mountedByOpenat2 is a method of detecting a mount that works for all kinds
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// of mounts (incl. bind mounts), but requires a recent (v5.6+) linux kernel.
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func mountedByOpenat2(path string) (bool, error) {
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@@ -34,24 +62,40 @@ func mountedByOpenat2(path string) (bool, error) {
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return false, &os.PathError{Op: "openat2", Path: path, Err: err}
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}
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-func mounted(path string) (bool, error) {
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- path, err := normalizePath(path)
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- if err != nil {
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- return false, err
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+// mountedFast is similar to MountedFast, except it expects a normalized path.
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+func mountedFast(path string) (mounted, sure bool, err error) {
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+ // Root is always mounted.
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+ if path == string(os.PathSeparator) {
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+ return true, true, nil
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}
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+
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// Try a fast path, using openat2() with RESOLVE_NO_XDEV.
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- mounted, err := mountedByOpenat2(path)
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+ mounted, err = mountedByOpenat2(path)
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if err == nil {
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- return mounted, nil
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+ return mounted, true, nil
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}
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+
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// Another fast path: compare st.st_dev fields.
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mounted, err = mountedByStat(path)
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// This does not work for bind mounts, so false negative
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// is possible, therefore only trust if return is true.
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if mounted && err == nil {
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+ return true, true, nil
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+ }
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+
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+ return
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+}
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+
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+func mounted(path string) (bool, error) {
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+ path, err := normalizePath(path)
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+ if err != nil {
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+ return false, err
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+ }
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+ mounted, sure, err := mountedFast(path)
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+ if sure && err == nil {
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return mounted, nil
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}
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- // Fallback to parsing mountinfo
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+ // Fallback to parsing mountinfo.
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return mountedByMountinfo(path)
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}
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Sebastiaan van Stijn