ustat returns information about a mounted file system. dev is a device number identifying a device containing a mounted file system. ubuf is a pointer to a ustat structure that contains the following members:
daddr_t f_tfree; /* Total free blocks */
ino_t f_tinode;/* Number of free inodes */
char f_fname; /* Filsys name */
char f_fpack; /* Filsys pack name */
The last two fields, f_fname and f_fpack, are not implemented and will always be filled with null characters.
On success, zero is returned and the ustat structure pointed to by ubuf will be filled in. On error, -1 is returned, and errno is set appropriately.