freebsd-skq/share/man/man9/vfsconf.9

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.Dd November 21, 2001
.Dt VFSCONF 9
.Os
.Sh NAME
.Nm vfsconf
.Nd "vfs configuration information"
.Sh SYNOPSIS
.In sys/param.h
.In sys/mount.h
.Ft int
.Fn vfs_register "struct vfsconf *vfc"
.Ft int
.Fn vfs_unregister "struct vfsconf *vfc"
.Ft int
.Fn vfs_modevent "module_t mod" "int type" "void *data"
.Sh DESCRIPTION
Each filesystem type known to the kernel has a
.Vt vfsconf
structure that contains the
information required to create a new mount of that filesystems type.
.Bd -literal
struct vfsconf {
	struct	vfsops *vfc_vfsops;	/* filesystem operations vector */
	char	vfc_name[MFSNAMELEN];	/* filesystem type name */
	int	vfc_typenum;		/* historic filesystem type number */
	int	vfc_refcount;		/* number mounted of this type */
	int	vfc_flags;		/* permanent flags */
	struct	vfsconf *vfc_next;	/* next in list */
};
.Ed
.Pp
When a new filesystem is mounted,
.Xr vfs_mount 9
does a lookup of the
.Vt vfsconf
structure by its name, and if it is not already registered,
attempts to load a kernel module for it.
The filesystem operations for the new mount point are taken from
.Va vfc_vfsops ,
and
.Va mnt_vfc
in the
.Vt mount
structure is made to point directly at the
.Vt vfsconf
structure for the
filesystem type.
The filesystem type number is taken from
.Va vfc_typenum
which was assigned in
.Fn vfs_register ,
and the mount flags are taken from a mask of
.Va vfc_flags .
Each time a filesystem of a given type is mounted,
.Va vfc_refcount
is incremented.
.Pp
.Fn vfs_register
takes a new
.Vt vfsconf
structure and adds it to the list of existing filesystems.
If the type has not already been registered, it is initialized by calling the
.Fn vfs_init
function in the filesystem operations vector.
.Fn vfs_register
also updates the oid's of any sysctl nodes for this filesystem type
to be the same as the newly assigned type number.
.Pp
.Fn vfs_unregister
unlinks
.Fa vfc
from the list of registered filesystem types if there are currently no mounted instances.
If the
.Fn vfs_uninit
function in the filesystems initialization vector is defined, it is called.
.Pp
.Fn vfs_modevent
is registered by
.Fn VFS_SET
to handle the loading and unloading of filesystem kernel modules.
In the case of
.Dv MOD_LOAD ,
.Fn vfs_register
is called.
In the case of
.Dv MOD_UNLOAD ,
.Fn vfs_unregister
is called.
.Sh RETURN VALUES
.Fn vfs_register
returns 0 if successful; otherwise,
.Er EEXIST
is returned indicating that the filesystem type has already been registered.
.Pp
.Fn vfs_unregister
returns 0 if successful.
If no
.Vt vfsconf
entry can be found matching the name in
.Fa vfc ,
.Er EINVAL
is returned.
If the reference count of mounted instances of the filesystem type is not zero,
.Er EBUSY
is returned.
If
.Fn vfs_uninit
is called, any errors it returns will be returned by
.Fn vfs_unregister .
.Pp
.Fn vfs_modevent
returns the result of the call to
.Fn vfs_register
or
.Fn vfs_unregister ,
whatever the case.
.Sh SEE ALSO
.Xr vfs_mount 9 ,
.Xr vfs_rootmountalloc 9 ,
.Xr VFS_SET 9
.Sh AUTHORS
This man page was written by
.An Chad David Aq davidc@acns.ab.ca .