AOSP utilises EXT4 for its root filesystem (like /data/media/0/; basically, all except mounted ones, for which I believe that solely exFAT is a possible alternative). EXT4 has no filesystem-defined maximum path length. ^[1] However, the Linux kernel does, exposed via PATH_MAX. It is usually 4096 characters. ^[2] Unfortunately, programmatically verifying (and, by extension, relying upon) it isn't recommended. ^[3]