DESCRIPTION
Each file system type known to the kernel has a
.Vt 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 */
intvfc_typenum; /* historic file system type number */
intvfc_refcount; /* number mounted of this type */
intvfc_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
.Vt 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
.Vt mount structure is made to point directly at the
.Vt 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
.Vt 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
.Vt 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
