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.Dd June 20, 2007 .Dt VFSOPS 9 .Os .Sh NAME .Nm vfsops , .Nm VFS_MOUNT , .Nm VFS_START , .Nm VFS_UNMOUNT , .Nm VFS_ROOT , .Nm VFS_QUOTACTL , .Nm VFS_STATVFS , .Nm VFS_SYNC , .Nm VFS_VGET , .Nm VFS_FHTOVP , .Nm VFS_VPTOFH , .Nm VFS_SNAPSHOT , .Nm VFS_SUSPENDCTL .Nd kernel file system interface .Sh SYNOPSIS n sys/param.h n sys/mount.h n sys/vnode.h .Ft int .Fn VFS_MOUNT "struct mount *mp" "const char *path" "void *data" \ "struct nameidata *ndp" "struct lwp *l" .Ft int .Fn VFS_START "struct mount *mp" "int flags" "struct lwp *l" .Ft int .Fn VFS_UNMOUNT "struct mount *mp" "int mntflags" "struct lwp *l" .Ft int .Fn VFS_ROOT "struct mount *mp" "struct vnode **vpp" .Ft int .Fn VFS_QUOTACTL "struct mount *mp" "int cmds" "uid_t uid" \ "void *arg" "struct lwp *l" .Ft int .Fn VFS_STATVFS "struct mount *mp" "struct statvfs *sbp" "struct lwp *l" .Ft int .Fn VFS_SYNC "struct mount *mp" "int waitfor" "kauth_cred_t cred" \ "struct lwp *l" .Ft int .Fn VFS_VGET "struct mount *mp" "ino_t ino" "struct vnode **vpp" .Ft int .Fn VFS_FHTOVP "struct mount *mp" "struct fid *fhp" "struct vnode **vpp" .Ft int .Fn VFS_VPTOFH "struct vnode *vp" "struct fid *fhp" "size_t *fh_size" .Ft int .Fn VFS_SNAPSHOT "struct mount *mp" "struct vnode *vp" "struct timespec *ts" .Ft int .Fn VFS_SUSPENDCTL "struct mount *mp" "int cmd" .Sh DESCRIPTION In a similar fashion to the .Xr vnode 9 interface, all operations that are done on a file system are conducted through a single interface that allows the system to carry out operations on a file system without knowing its construction or type.
p All supported file systems in the kernel have an entry in the .Va vfs_list_initial table. This table is generated by .Xr config 1 and is a .Dv NULL Ns No -terminated list of .Em vfsops structures. The vfsops structure describes the operations that can be done to a specific file system type. The following table lists the elements of the vfsops vector, the corresponding invocation macro, and a description of the element.
p
Vector element Macro Description int (*vfs_mount)() VFS_MOUNT Mount a file system int (*vfs_start)() VFS_START Make operational int (*vfs_unmount)() VFS_UMOUNT Unmount a file system int (*vfs_root)() VFS_ROOT Get the file system root vnode int (*vfs_quotactl)() VFS_QUOTACTL Query/modify space quotas int (*vfs_statvfs)() VFS_STATVFS Get file system statistics int (*vfs_sync)() VFS_SYNC Flush file system buffers int (*vfs_vget)() VFS_VGET Get vnode from file id int (*vfs_fhtovp)() VFS_FHTOVP NFS file handle to vnode lookup int (*vfs_vptofh)() VFS_VPTOFH Vnode to NFS file handle lookup void (*vfs_init)() - Initialise file system void (*vfs_reinit)() - Reinitialise file system void (*vfs_done)() - Cleanup unmounted file system int (*vfs_mountroot)() - Mount the root file system int (*vfs_snapshot)() VFS_SNAPSHOT Take a snapshot int (*vfs_suspendctl)() VFS_SUSPENDCTL Suspend or resume
p Some additional non-function members of the vfsops structure are the file system name .Ns Em vfs_name and a reference count .Ns Em vfs_refcount . It is not mandatory for a file system type to support a particular operation, but it must assign each member function pointer to a suitable function to do the minimum required of it. In most cases, such functions either do nothing or return an error value to the effect that it is not supported. .Em vfs_reinit , .Em vfs_mountroot , .Em vfs_fhtovp , and .Em vfs_vptofh may be .Dv NULL .
p At system boot, each file system with an entry in .Va vfs_list_initial is established and initialised. Each initialised file system is recorded by the kernel in the list .Va vfs_list and the file system specific initialisation function .Em vfs_init in its vfsops vector is invoked. When the file system is no longer needed .Em vfs_done is invoked to run file system specific cleanups and the file system is removed from the kernel list.
p At system boot, the root filesystem is mounted by invoking the file system type specific .Em vfs_mountroot function in the vfsops vector. All filesystems that can be mounted as a root file system must define this function. It is responsible for initialising to list of mount structures for all future mounted file systems.
p Kernel state which affects a specific file system type can be queried and modified using the .Xr sysctl 8 interface. .Sh FUNCTIONS l -tag -width compact t Fn VFS_MOUNT "mp" "path" "data" "ndp" "l" Mount a file system specified by the mount structure .Fa mp on the mount point described by .Fa path . The argument .Fa data contains file system type specific data and is read into the kernel using .Xr copyin 9 . The argument .Fa ndp contains the result of a .Xr namei 9 call on the pathname of the mount point and .Fa l is the calling lwp. .Fn VFS_MOUNT initialises the mount structure for the mounted file system. This structure records mount-specific information for the file system and records the list of vnodes associated with the file system. This function is invoked both to mount new file systems and to change the attributes of an existing file system. If the MNT_UPDATE flag is set in .Em mp-\*[Gt]mnt_flag then the filesystem should update its internal state from the value of .Em mp-\*[Gt]mnt_flag . This can be used, for instance, to convert a read-only filesystem to read-write. If the MNT_UPDATE flag is not specified, then this is a newly mounted filesystem. t Fn VFS_START "mp" "flags" "l" Make the file system specified by the mount structure .Fa mp operational. The argument .Fa l is the calling lwp. The argument .Fa flags is a set of flags for controlling the operation of .Fn VFS_START . This function is invoked after .Fn VFS_MOUNT and before the first access to the file system. t Fn VFS_UNMOUNT "mp" "mntflags" "l" Unmount a file system specified by the mount structure .Fa mp . The argument .Fa l is the calling lwp. .Fn VFS_UNMOUNT performs any file system type specific operations required before the file system is unmounted, such are flushing buffers. If MNT_FORCE is specified in the flags .Fa mntflags then open files are forcibly closed. The function also deallocates space associated with data structure that were allocated for the file system when it was mounted. t Fn VFS_ROOT "mp" "vpp" Get the root vnode of the file system specified by the mount structure .Fa mp . The vnode is returned in the address given by .Fa vpp . This function is used by the pathname translation algorithms when a vnode that has been covered by a mounted file system is encountered. While resolving the pathname, the pathname translation algorithm will have to go through the directory tree in the file system associated with that mount point and therefore requires the root vnode of the file system. t Fn VFS_QUOTACTL "mp" "cmds" "uid" "arg" "l" Query/modify user space quotas for the file system specified by the mount structure .Fa mp . The argument specifies the control command to perform. The userid is specified in .Fa id , the calling lwp is .Fa l and .Fa arg allows command-specific data to be returned to the system call interface. .Fn VFS_QUOTACTL is the file system type specific implementation of the .Xr quotactl 2 system call. t Fn VFS_STATVFS "mp" "sbp" "l" Get file system statistics for the file system specified by the mount structure .Fa mp . The argument .Fa l is the calling lwp. A statvfs structure filled with the statistics is returned in .Fa sbp . .Fn VFS_STATVFS is the file system type specific implementation of the .Xr statvfs 2 and .Xr fstatvfs 2 system calls. t Fn VFS_SYNC "mp" "waitfor" "cred" "l" Flush file system I/O buffers for the file system specified by the mount structure .Fa mp . The .Fa waitfor argument indicates whether a partial flush or complete flush should be performed. The arguments .Fa l and .Fa cred specific the calling lwp and its credentials, respectively. .Fn VFS_SYNC does not provide any return value since the operation can never fail. t Fn VFS_VGET "mp" "ino" "vpp" Get vnode for a file system type specific file id .Fa ino for the file system specified by the mount structure .Fa mp . The vnode is returned in the address specified .Fa vpp . The function is optional for file systems which have a unique id number for every file in the file system. It is used internally by the UFS file system and also by the NFSv3 server to implement the READDIRPLUS nfs call. If the file system does not support this function, it should return .Er EOPNOTSUPP . t Fn VFS_FHTOVP "mp" "fhp" "vpp" Get the vnode for the file handle .Fa fhp in the file system specified by the mount structure .Fa mp . The locked vnode is returned in .Fa vpp .
p When exporting, the call to .Fn VFS_FHTOVP should follow a call to .Fn netexport_check , which checks if the file is accessable to the client.
p If file handles are not supported by the file system, this function must return .Er EOPNOTSUPP . t Fn VFS_VPTOFH "vp" "fhp" "fh_size" Get a file handle for the vnode specified by .Fa vp . The file handle is returned in .Fa fhp . The contents of the file handle are defined by the file system and are not examined by any other subsystems. It should contain enough information to uniquely identify a file within the file system as well as noticing when a file has been removed and the file system resources have been recycled for a new file.
p The parameter .Fa fh_size points to the container size for the file handle. This parameter should be updated to the size of the finished file handle. Note that it is legal to call this function with .Fa fhp set to .Dv NULL in case .Fa fh_size is zero. In case .Fa fh_size indicates a storage space too small, the storage space required for the file handle corresponding to .Fa vp should be filled in and .Er E2BIG should be returned.
p If file handles are not supported by the file system, this function must return .Er EOPNOTSUPP . t Fn VFS_SNAPSHOT "mp" "vp" "ts" Take a snapshot of the file system specified by the mount structure .Fa mp and make it accessible through the locked vnode .Fa vp . If .Fa ts is not .Dv NULL it will receive the time this snapshot was taken. If the file system does not support this function, it should return .Er EOPNOTSUPP . t Fn VFS_SUSPENDCTL "mp" "cmd" Suspend or resume all operations on this file system. .Fa cmd is either .Dv SUSPEND_SUSPEND to suspend or .Dv SUSPEND_RESUME to resume operations. If the file system does not support this function, it should return .Er EOPNOTSUPP . .El .Sh CODE REFERENCES This section describes places within the .Nx source tree where actual code implementing or using the vfs operations can be found. All pathnames are relative to
p The vfs operations are implemented within the files
a sys/kern/vfs_subr.c and
a sys/kern/vfs_init.c . .Sh SEE ALSO .Xr intro 9 , .Xr namei 9 , .Xr vfs 9 , .Xr vfssubr 9 , .Xr vnode 9 , .Xr vnodeops 9 .Sh HISTORY The vfs operations vector, its functions and the corresponding macros appeared in x 4.3 .
Indexes created Sun Oct 19 16:10:00 GMT 2025