NAME

     vfsconf — vfs configuration information

SYNOPSIS

     #include <sys/param.h>
     #include <sys/mount.h>

     int
     vfs_register(struct vfsconf *vfc);

     int
     vfs_unregister(struct vfsconf *vfc);

     int
     vfs_modevent(module_t mod, int type, void *data);

DESCRIPTION

     Each file system type known to the kernel has a vfsconf structure that contains the
     information required to create a new mount of that file systems type.

     struct vfsconf {
             struct  vfsops *vfc_vfsops;     /* file system operations vector */
             char    vfc_name[MFSNAMELEN];   /* file system type name */
             int     vfc_typenum;            /* historic file system type number */
             int     vfc_refcount;           /* number mounted of this type */
             int     vfc_flags;              /* permanent flags */
             struct  vfsconf *vfc_next;      /* next in list */
     };

     When a new file system is mounted, mount(2) does a lookup of the vfsconf structure by its
     name, and if it is not already registered, attempts to load a kernel module for it.  The
     file system operations for the new mount point are taken from vfc_vfsops, and mnt_vfc in the
     mount structure is made to point directly at the vfsconf structure for the file system type.
     The file system type number is taken from vfc_typenum which was assigned in vfs_register(),
     and the mount flags are taken from a mask of vfc_flags.  Each time a file system of a given
     type is mounted, vfc_refcount is incremented.

     vfs_register() takes a new vfsconf structure and adds it to the list of existing file
     systems.  If the type has not already been registered, it is initialized by calling the
     vfs_init() function in the file system operations vector.  vfs_register() also updates the
     oid's of any sysctl nodes for this file system type to be the same as the newly assigned
     type number.

     vfs_unregister() unlinks vfc from the list of registered file system types if there are
     currently no mounted instances.  If the vfs_uninit() function in the file systems
     initialization vector is defined, it is called.

     vfs_modevent() is registered by VFS_SET() to handle the loading and unloading of file system
     kernel modules.  In the case of MOD_LOAD, vfs_register() is called.  In the case of
     MOD_UNLOAD, vfs_unregister() is called.

RETURN VALUES

     vfs_register() returns 0 if successful; otherwise, EEXIST is returned indicating that the
     file system type has already been registered.

     vfs_unregister() returns 0 if successful.  If no vfsconf entry can be found matching the
     name in vfc, EINVAL is returned.  If the reference count of mounted instances of the file
     system type is not zero, EBUSY is returned.  If vfs_uninit() is called, any errors it
     returns will be returned by vfs_unregister().

     vfs_modevent() returns the result of the call to vfs_register() or vfs_unregister(),
     whatever the case.

SEE ALSO

     mount(2), vfs_rootmountalloc(9), VFS_SET(9)

AUTHORS

     This manual page was written by Chad David <davidc@acns.ab.ca>.