VFSOPS(9) BSD 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_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_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 know‐
ing 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 corre‐
sponding 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_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 initializa‐
tion 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 spe‐
cific cleanups and the file system is removed from the kernel list.
At system boot, the root file system is mounted by invoking the file sys‐
tem type specific vfs_mountroot function in the vfsops vector. All file
systems that can be mounted as a root file system must define this func‐
tion. 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 specify‐
ing MNT_GETARGS. If neither MNT_UPDATE or MNT_GETARGS are spec‐
ified, a new file system will attempted to be mounted.
VFS_START(mp, flags)
Make the file system specified by the mount structure mp opera‐
tional. 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 algo‐
rithms when a vnode that has been covered by a mounted file sys‐
tem 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 there‐
fore 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 inter‐
face as documented in __quotactl(2) except that the file system
argument has been resolved. All copyin(9) and copyout(9) pro‐
cessing 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 statis‐
tics 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_FHTOVP(mp, fhp, vpp)
Get the vnode for the file handle fhp in the file system speci‐
fied 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 func‐
tion must return EOPNOTSUPP.
VFS_VPTOFH(vp, fhp, fh_size)
Get a file handle for the vnode specified by vp. The file han‐
dle 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 func‐
tion 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 func‐
tion must return EOPNOTSUPP.
VFS_SNAPSHOT(mp, vp, ts)
Take a snapshot of the file system specified by the mount struc‐
ture 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 ALSOintro(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.
BSD February 13, 2012 BSD
