usr/sys/filsys.h

/*
 * Definition of the unix super block.
 * The root super block is allocated and
 * read in iinit/alloc.c. Subsequently
 * a super block is allocated and read
 * with each mount (smount/sys3.c) and
 * released with unmount (sumount/sys3.c).
 * A disk block is ripped off for storage.
 * See alloc.c for general alloc/free
 * routines for free list and I list.
 */
struct  filsys
{
        int     s_isize;        /* size in blocks of I list */
        int     s_fsize;        /* size in blocks of entire volume */
        int     s_nfree;        /* number of in core free blocks (0-100) */
        int     s_free[100];    /* in core free blocks */
        int     s_ninode;       /* number of in core I nodes (0-100) */
        int     s_inode[100];   /* in core free I nodes */
        char    s_flock;        /* lock during free list manipulation */
        char    s_ilock;        /* lock during I list manipulation */
        char    s_fmod;         /* super block modified flag */
        char    s_ronly;        /* mounted read-only flag */
        int     s_time[2];      /* current date of last update */
        int     pad[50];
};