mount-util: tape over name_to_handle_at() flakiness (#7517)

Apparently, the kernel returns EINVAL on NFS4 sometimes, even if we do
everything right, let's fallback in that case and find a different
approach to determine if something's a mount point.

See discussion at:

https://github.com/systemd/systemd/issues/7082#issuecomment-348001289

diff --git a/src/basic/mount-util.c b/src/basic/mount-util.c
index e32502308a72be30f9b161efe41791d8e16e9707..e394e1adf314cf9ad655d37a5e8e25acce658a9e 100644 (file)
--- a/src/basic/mount-util.c
+++ b/src/basic/mount-util.c
@@ -183,10 +183,11 @@ int fd_is_mount_point(int fd, const char *filename, int flags) {
          * real mounts of their own. */
 
         r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags);
-        if (IN_SET(r, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW))
+        if (IN_SET(r, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL))
                 /* This kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall was blocked
                  * (EACCES/EPERM; maybe through seccomp, because we are running inside of a container?), or the mount
-                 * point is not triggered yet (EOVERFLOW, thinkg nfs4): fall back to simpler logic. */
+                 * point is not triggered yet (EOVERFLOW, think nfs4), or some general name_to_handle_at() flakiness
+                 * (EINVAL): fall back to simpler logic. */
                 goto fallback_fdinfo;
         else if (r == -EOPNOTSUPP)
                 /* This kernel or file system does not support name_to_handle_at(), hence let's see if the upper fs
@@ -308,7 +309,7 @@ int path_get_mnt_id(const char *path, int *ret) {
         int r;
 
         r = name_to_handle_at_loop(AT_FDCWD, path, NULL, ret, 0);
-        if (IN_SET(r, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW)) /* kernel/fs don't support this, or seccomp blocks access, or untriggered mount */
+        if (IN_SET(r, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) /* kernel/fs don't support this, or seccomp blocks access, or untriggered mount, or name_to_handle_at() is flaky */
                 return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret);
 
         return r;