initial_sid_contexts – platform/external/sepolicy – Git at Google (googlesource.com)
FileStatements – SELinux Wiki (selinuxproject.org)
mount options :
mount -ocontext=u:object_r:vfat1:s0 /dev/block1 /mnt/vfat1
mount -ocontext=u:object_r:vfat1:s0 /dev/block2 /mnt/vfat2