Support the MS_NOSYMFOLLOW mount flag.  Added to Chrome OS in 5.4 and sent
upstream as:

https://lore.kernel.org/linux-fsdevel/20200304173446.122990-1-zwisler@google.com/

See b/152074038 for background.

diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c
index 088d1328e..5cce46556 100644
--- a/libmount/src/context_mount.c
+++ b/libmount/src/context_mount.c
@@ -422,6 +422,8 @@ static int generate_helper_optstr(struct libmnt_context *cxt, char **optstr)
 			mnt_optstr_append_option(optstr, "suid", NULL);
 		if (!(cxt->mountflags & MS_NODEV))
 			mnt_optstr_append_option(optstr, "dev", NULL);
+		if (!(cxt->mountflags & MS_NOSYMFOLLOW))
+			mnt_optstr_append_option(optstr, "symfollow", NULL);
 	}
 
 
diff --git a/libmount/src/libmount.h.in b/libmount/src/libmount.h.in
index 321c0540b..e6710ae01 100644
--- a/libmount/src/libmount.h.in
+++ b/libmount/src/libmount.h.in
@@ -941,6 +941,9 @@ extern int mnt_context_set_syscall_status(struct libmnt_context *cxt, int status
 #ifndef MS_DIRSYNC
 #define MS_DIRSYNC	128	/* Directory modifications are synchronous */
 #endif
+#ifndef MS_NOSYMFOLLOW
+#define MS_NOSYMFOLLOW	256	/* Don't follow symlinks */
+#endif
 #ifndef MS_NOATIME
 #define MS_NOATIME	0x400	/* 1024: Do not update access times. */
 #endif
diff --git a/libmount/src/optmap.c b/libmount/src/optmap.c
index abd81bc8e..731771327 100644
--- a/libmount/src/optmap.c
+++ b/libmount/src/optmap.c
@@ -131,6 +131,10 @@ static const struct libmnt_optmap linux_flags_map[] =
    { "rslave",      MS_SLAVE | MS_REC,      MNT_NOHLPS | MNT_NOMTAB },
    { "shared",      MS_SHARED,              MNT_NOHLPS | MNT_NOMTAB }, /* Shared */
    { "rshared",     MS_SHARED | MS_REC,     MNT_NOHLPS | MNT_NOMTAB },
+#endif
+#ifdef MS_NOSYMFOLLOW
+   { "symfollow", MS_NOSYMFOLLOW, MNT_INVERT }, /* Don't follow symlinks */
+   { "nosymfollow", MS_NOSYMFOLLOW },
 #endif
    { NULL, 0, 0 }
 };