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VFSCONF(9) FreeBSD Kernel Developer's Manual VFSCONF(9)

vfs configuration information

#include <sys/param.h>
#include <sys/mount.h>
vfs_register(struct vfsconf *vfc);
vfs_unregister(struct vfsconf *vfc);
vfs_modevent(module_t mod, int type, void *data);

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.

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.

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

This manual page was written by Chad David <>.
June 16, 2013 FreeBSD 12.0-RELEASE

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