| VNODE(9) | Kernel Developer's Manual | VNODE(9) |
void
vref(struct vnode *vp);
void
vrele(struct vnode *vp);
void
vrele_async(struct vnode *vp);
int
vget(struct vnode *vp, int lockflag);
void
vput(struct vnode *vp);
void
vhold(struct vnode *vp);
void
holdrele(struct vnode *vp);
int
getnewvnode(enum vtagtype tag, struct mount *mp, int (**vops)(void *), kmutex_t *slock, struct vnode **vpp);
void
ungetnewvnode(struct vnode *vp);
int
vrecycle(struct vnode *vp, struct simplelock *inter_lkp, struct lwp *l);
void
vgone(struct vnode *vp);
void
vgonel(struct vnode *vp, struct lwp *l);
int
vflush(struct mount *mp, struct vnode *skipvp, int flags);
int
vaccess(enum vtype type, mode_t file_mode, uid_t uid, gid_t gid, mode_t acc_mode, kauth_cred_t cred);
int
bdevvp(dev_t dev, struct vnode **vpp);
int
cdevvp(dev_t dev, struct vnode **vpp);
int
vfinddev(dev_t dev, enum vtype, struct vnode **vpp);
void
vdevgone(int maj, int minl, int minh, enum vtype type);
void
vwakeup(struct buf *bp);
int
vflushbuf(struct vnode *vp, int sync);
int
vinvalbuf(struct vnode *vp, int flags, kauth_cred_t cred, struct lwp *l, int slpflag, int slptimeo);
int
vtruncbuf(struct vnode *vp, daddr_t lbn, int slpflag, int slptimeo);
void
vprint(const char *label, struct vnode *vp);
When a process requests an operation on a file, the vfs(9) interface passes control to a file system type dependent function to carry out the operation. If the file system type dependent function finds that a vnode representing the file is not in main memory, it dynamically allocates a new vnode from the system main memory pool. Once allocated, the vnode is attached to the data structure pointer associated with the cause of the vnode allocation and it remains resident in the main memory until the system decides that it is no longer needed and can be recycled.
The vnode has the following structure:
struct vnode {
struct uvm_object v_uobj; /* the VM object */
kcondvar_t v_cv; /* synchronization */
voff_t v_size; /* size of file */
voff_t v_writesize; /* new size after write */
int v_iflag; /* VI_* flags */
int v_vflag; /* VV_* flags */
int v_uflag; /* VU_* flags */
int v_numoutput; /* # of pending writes */
int v_writecount; /* ref count of writers */
int v_holdcnt; /* page & buffer refs */
int v_synclist_slot; /* synclist slot index */
struct mount *v_mount; /* ptr to vfs we are in */
int (**v_op)(void *); /* vnode operations vector */
TAILQ_ENTRY(vnode) v_freelist; /* vnode freelist */
struct vnodelst *v_freelisthd; /* which freelist? */
TAILQ_ENTRY(vnode) v_mntvnodes; /* vnodes for mount point */
struct buflists v_cleanblkhd; /* clean blocklist head */
struct buflists v_dirtyblkhd; /* dirty blocklist head */
TAILQ_ENTRY(vnode) v_synclist; /* vnodes with dirty bufs */
LIST_HEAD(, namecache) v_dnclist; /* namecaches (children) */
LIST_HEAD(, namecache) v_nclist; /* namecaches (parent) */
union {
struct mount *vu_mountedhere;/* ptr to vfs (VDIR) */
struct socket *vu_socket; /* unix ipc (VSOCK) */
struct specnode *vu_specnode; /* device (VCHR, VBLK) */
struct fifoinfo *vu_fifoinfo; /* fifo (VFIFO) */
struct uvm_ractx *vu_ractx; /* read-ahead ctx (VREG) */
} v_un;
enum vtype v_type; /* vnode type */
enum vtagtype v_tag; /* type of underlying data */
struct vnlock v_lock; /* lock for this vnode */
void *v_data; /* private data for fs */
struct klist v_klist; /* notes attached to vnode */
};
Most members of the vnode structure should be treated as opaque and only manipulated using the proper functions. There are some rather common exceptions detailed throughout this page.
Files and file systems are inextricably linked with the virtual memory system and v_uobj contains the data maintained by the virtual memory system. For compatibility with code written before the integration of uvm(9) into NetBSD, C-preprocessor directives are used to alias the members of v_uobj.
Vnode flags are recorded by v_flag. Valid flags are:
The VXLOCK flag is used to prevent multiple processes from entering the vnode reclamation code. It is also used as a flag to indicate that reclamation is in progress. The VXWANT flag is set by threads that wish to be awakened when reclamation is finished. Before v_flag can be modified, the v_interlock simplelock must be acquired. See lock(9) for details on the kernel locking API.
Each vnode has three reference counts: v_usecount, v_writecount and v_holdcnt. The first is the number of active references within the kernel to the vnode. This count is maintained by vref(), vrele(), vrele_async(), and vput(). The second is the number of active references within the kernel to the vnode performing write access to the file. It is maintained by the open(2) and close(2) system calls. The third is the number of references within the kernel requiring the vnode to remain active and not be recycled. This count is maintained by vhold() and holdrele(). When both the v_usecount and v_holdcnt reach zero, the vnode is recycled to the freelist and may be reused for another file. The transition to and from the freelist is handled by getnewvnode(), ungetnewvnode() and vrecycle(). Access to v_usecount, v_writecount and v_holdcnt is also protected by the v_interlock simplelock.
The number of pending synchronous and asynchronous writes on the vnode are recorded in v_numoutput. It is used by fsync(2) to wait for all writes to complete before returning to the user. Its value must only be modified at splbio (see spl(9)). It does not track the number of dirty buffers attached to the vnode.
v_dnclist and v_nclist are used by namecache(9) to maintain the list of associated entries so that cache_purge(9) can purge them.
The link to the file system which owns the vnode is recorded by v_mount. See vfsops(9) for further information of file system mount status.
The v_op pointer points to its vnode operations vector. This vector describes what operations can be done to the file associated with the vnode. The system maintains one vnode operations vector for each file system type configured into the kernel. The vnode operations vector contains a pointer to a function for each operation supported by the file system. See vnodeops(9) for a description of vnode operations.
When not in use, vnodes are kept on the freelist through v_freelist. The vnodes still reference valid files but may be reused to refer to a new file at any time. When a valid vnode which is on the freelist is used again, the user must call vget() to increment the reference count and retrieve it from the freelist. When a user wants a new vnode for another file, getnewvnode() is invoked to remove a vnode from the freelist and initialize it for the new file.
The type of object the vnode represents is recorded by v_type. It is used by generic code to perform checks to ensure operations are performed on valid file system objects. Valid types are:
Vnode tag types are used by external programs only (e.g., pstat(8)), and should never be inspected by the kernel. Its use is deprecated since new v_tag values cannot be defined for loadable file systems. The v_tag member is read-only. Valid tag types are:
All vnode locking operations use v_lock. This lock is acquired by calling vn_lock(9) and released by calling VOP_UNLOCK(9). The reason for this asymmetry is that vn_lock(9) is a wrapper for VOP_LOCK(9) with extra checks, while the unlocking step usually does not need additional checks and thus has no wrapper.
The vnode locking operation is complicated because it is used for many purposes. Sometimes it is used to bundle a series of vnode operations (see vnodeops(9)) into an atomic group. Many file systems rely on it to prevent race conditions in updating file system type specific data structures rather than using their own private locks. The vnode lock can operate as a multiple-reader (shared-access lock) or single-writer lock (exclusive access lock), however many current file system implementations were written assuming only single-writer locking. Multiple-reader locking functions equivalently only in the presence of big-lock SMP locking or a uni-processor machine. The lock may be held while sleeping. While the v_lock is acquired, the holder is guaranteed that the vnode will not be reclaimed or invalidated. Most file system functions require that you hold the vnode lock on entry. See lock(9) for details on the kernel locking API.
Each file system underlying a vnode allocates its own private area and hangs it from v_data.
Most functions discussed in this page that operate on vnodes cannot be called from interrupt context. The members v_numoutput, v_holdcnt, v_dirtyblkhd, v_cleanblkhd, v_freelist, and v_synclist are modified in interrupt context and must be protected by splbio(9) unless it is certain that there is no chance an interrupt handler will modify them. The vnode lock must not be acquired within interrupt context.
The argument mp is the mount point for the file system requested the new vnode. Before retrieving the new vnode, the file system is checked if it is busy (such as currently unmounting). An error is returned if the file system is unmounted.
The argument tag is the vnode tag assigned to *vpp->v_tag. The argument vops is the vnode operations vector of the file system requesting the new vnode. If a vnode is successfully retrieved zero is returned, otherwise an appropriate error code is returned. If slock is not NULL, it specifies the lock to share for v_interlock. The reference will be held on the lock and sharing noted. Reference will be released and lock unshared when the vnode gets recycled. If NULL (regular case), vnode will use its own interlock.
| February 8, 2012 | NetBSD 6.1 |