VFSOPS(9) | Kernel Developer's Manual | VFSOPS(9)

# NAME

`vfsops`, `VFS_MOUNT`, `VFS_START`, `VFS_UNMOUNT`, `VFS_ROOT`, `VFS_QUOTACTL`, `VFS_STATVFS`, `VFS_SYNC`, `VFS_VGET`, `VFS_LOADVNODE`, `VFS_NEWVNODE`, `VFS_FHTOVP`, `VFS_VPTOFH`, `VFS_SNAPSHOT`, `VFS_SUSPENDCTL` —
kernel file system interface

# SYNOPSIS

`#include <sys/param.h>`
`#include <sys/mount.h>`
`#include <sys/vnode.h>`

int
`VFS_MOUNT`(struct mount *mp, const char *path, void *data, size_t *dlen);

int
`VFS_START`(struct mount *mp, int flags);

int
`VFS_UNMOUNT`(struct mount *mp, int mntflags);

int
`VFS_ROOT`(struct mount *mp, struct vnode **vpp);

int
`VFS_QUOTACTL`(struct mount *mp, struct quotactl_args *args);

int
`VFS_STATVFS`(struct mount *mp, struct statvfs *sbp);

int
`VFS_SYNC`(struct mount *mp, int waitfor, kauth_cred_t cred);

int
`VFS_VGET`(struct mount *mp, ino_t ino, struct vnode **vpp);

int
`VFS_LOADVNODE`(struct mount *mp, struct vnode *vp, const void *key, size_t key_len, const void **new_key);

int
`VFS_NEWVNODE`(struct mount *mp, struct vnode *dvp, struct vnode *vp, struct vattr *vap, kauth_cred_t cred, void *extra, size_t *key_len, const void **new_key);

int
`VFS_FHTOVP`(struct mount *mp, struct fid *fhp, struct vnode **vpp);

int
`VFS_VPTOFH`(struct vnode *vp, struct fid *fhp, size_t *fh_size);

int
`VFS_SNAPSHOT`(struct mount *mp, struct vnode *vp, struct timespec *ts);

int
`VFS_SUSPENDCTL`(struct mount *mp, int cmd);

# DESCRIPTION

In a similar fashion to the 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.

All supported file systems in the kernel have an entry in the vfs_list_initial table. This table is generated by config(1) and is a `NULL`-terminated list of 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.

Vector element | Macro | Description
int (*vfs_mount)() | `VFS_MOUNT` | Mount a file system
int (*vfs_start)() | `VFS_START` | Make operational
int (*vfs_unmount)() | `VFS_UNMOUNT` | 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_loadvnode)() | `VFS_LOADVNODE` | Initialze vnode with file
int (*vfs_loadvnode)() | `VFS_NEWVNODE` | Initialze vnode with new file
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)() | - | Initialize file system
void (*vfs_reinit)() | - | Reinitialize 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

Some additional non-function members of the vfsops structure are the file system name vfs_name and a reference count 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. vfs_reinit, vfs_mountroot, vfs_fhtovp, and vfs_vptofh may be `NULL`.

At system boot, each file system with an entry in vfs_list_initial is established and initialized. Each initialized file system is recorded by the kernel in the list vfs_list and the file system specific initialization function vfs_init in its vfsops vector is invoked. When the file system is no longer needed vfs_done is invoked to run file system specific cleanups and the file system is removed from the kernel list.

At system boot, the root file system is mounted by invoking the file system type specific vfs_mountroot function in the vfsops vector. All file systems that can be mounted as a root file system must define this function. It is responsible for initializing to list of mount structures for all future mounted file systems.

Kernel state which affects a specific file system type can be queried and modified using the sysctl(8) interface.

# FUNCTIONS

`VFS_MOUNT`(mp, path, data, dlen)
  Mount a file system specified by the mount structure mp on the mount point described by path. The argument data contains file system type specific data, while the argument dlen points to a location specifying the length of the data.

  `VFS_MOUNT`() initializes 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 flag `MNT_UPDATE` is set in mp->mnt_flag, the file system should update its state. This can be used, for instance, to convert a read-only file system to read-write. The current attributes for a mounted file system can be fetched by specifying `MNT_GETARGS`. If neither `MNT_UPDATE` or `MNT_GETARGS` are specified, a new file system will attempted to be mounted.

`VFS_START`(mp, flags)
  Make the file system specified by the mount structure mp operational. The argument flags is a set of flags for controlling the operation of `VFS_START`(). This function is invoked after `VFS_MOUNT`() and before the first access to the file system.
`VFS_UNMOUNT`(mp, mntflags)
  Unmount a file system specified by the mount structure mp. `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 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.
`VFS_ROOT`(mp, vpp)
  Get the root vnode of the file system specified by the mount structure mp. The vnode is returned in the address given by 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.
`VFS_QUOTACTL`(mp, args)
  Query/modify user space quotas for the file system specified by the mount structure mp. The argument structure provides the operation ID and arguments to perform. This is the same interface as documented in __quotactl(2) except that the file system argument has been resolved. All copyin(9) and copyout(9) processing is handled by code above the file system.
`VFS_STATVFS`(mp, sbp)
  Get file system statistics for the file system specified by the mount structure mp. A statvfs structure filled with the statistics is returned in sbp. `VFS_STATVFS`() is the file system type specific implementation of the statvfs(2) and fstatvfs(2) system calls.
`VFS_SYNC`(mp, waitfor, cred)
  Flush file system I/O buffers for the file system specified by the mount structure mp. The waitfor argument indicates whether a partial flush or complete flush should be performed. The argument cred specifies the calling credentials. `VFS_SYNC`() does not provide any return value since the operation can never fail.
`VFS_VGET`(mp, ino, vpp)
  Get vnode for a file system type specific file id ino for the file system specified by the mount structure mp. The vnode is returned in the address specified 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 `EOPNOTSUPP`.
`VFS_LOADVNODE`(mp, vp, key, key_len, new_key)
  Initialise the vnode vp with the file identified by the arguments key and key_len for the file system specified by the mount structure mp.

  The new key is returned in the address specified by new_key.

  Caller of this function assures no other thread will try to load this file.

`VFS_NEWVNODE`(mp, dvp, vp, vap, cred, key_len, new_key)
  Initialise the vnode vp with a new file for the file system specified by the mount structure mp.

  The argument dvp points to the directory to create the file in.

  The argument vap points to the attributes for the file to create.

  The argument cred holds the credentials for the file to create.

  The argument extra allows the caller to pass more information about the file to create.

  The key for the file is returned in the addresses specified by key_len and new_key.

`VFS_FHTOVP`(mp, fhp, vpp)
  Get the vnode for the file handle fhp in the file system specified by the mount structure mp. The locked vnode is returned in vpp.

  When exporting, the call to `VFS_FHTOVP`() should follow a call to `netexport_check`(), which checks if the file is accessible to the client.

  If file handles are not supported by the file system, this function must return `EOPNOTSUPP`.

`VFS_VPTOFH`(vp, fhp, fh_size)
  Get a file handle for the vnode specified by vp. The file handle is returned in 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.

  The parameter 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 fhp set to `NULL` in case fh_size is zero. In case fh_size indicates a storage space too small, the storage space required for the file handle corresponding to vp should be filled in and `E2BIG` should be returned.

  If file handles are not supported by the file system, this function must return `EOPNOTSUPP`.

`VFS_SNAPSHOT`(mp, vp, ts)
  Take a snapshot of the file system specified by the mount structure mp and make it accessible through the locked vnode vp. If ts is not `NULL` it will receive the time this snapshot was taken. If the file system does not support this function, it should return `EOPNOTSUPP`.
`VFS_SUSPENDCTL`(mp, cmd)
  Suspend or resume all operations on this file system. cmd is either `SUSPEND_SUSPEND` to suspend or `SUSPEND_RESUME` to resume operations. If the file system does not support this function, it should return `EOPNOTSUPP`.

# CODE REFERENCES

The vfs operations are implemented within the files sys/kern/vfs_subr.c and sys/kern/vfs_init.c.

# SEE ALSO

intro(9), namei(9), vfs(9), vfssubr(9), vnode(9), vnodeops(9)

# HISTORY

The vfs operations vector, its functions and the corresponding macros appeared in 4.3BSD.

January 1, 2019 | NetBSD 9.3