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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, vfs_mount(9) 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

     vfs_mount(9), vfs_rootmountalloc(9), VFS_SET(9)

AUTHORS

     This manual page was written by Chad David 〈davidc@acns.ab.ca〉.