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>.

Debian                                            June 16, 2013                                       VFSCONF(9)