V7/usr/include/sys/mount.h

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/*
 * Mount structure.
 * One allocated on every mount.
 * Used to find the super block.
 */
struct	mount
{
	dev_t	m_dev;		/* device mounted */
	struct buf *m_bufp;	/* pointer to superblock */
	struct inode *m_inodp;	/* pointer to mounted on inode */
} mount[NMOUNT];