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NetBSD 6.1.5 - man page for vinvalbuf (netbsd section 9)

VNODE(9)			  BSD Kernel Developer's Manual 			 VNODE(9)

NAME
     vnode, vref, vrele, vrele_async, vget, vput, vhold, holdrele, getnewvnode, ungetnewvnode,
     vrecycle, vgone, vgonel, vflush, vaccess, bdevvp, cdevvp, vfinddev, vdevgone, vwakeup,
     vflushbuf, vinvalbuf, vtruncbuf, vprint -- kernel representation of a file or directory

SYNOPSIS
     #include <sys/param.h>
     #include <sys/vnode.h>

     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);

DESCRIPTION
     The vnode is the focus of all file activity in NetBSD.  There is a unique vnode allocated
     for each active file, directory, mounted-on file, fifo, domain socket, symbolic link and
     device.  The kernel has no concept of a file's underlying structure and so it relies on the
     information stored in the vnode to describe the file.  Thus, the vnode associated with a
     file holds all the administration information pertaining to it.

     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 dynam-
     ically 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:

	   VROOT       This vnode is the root of its file system.
	   VTEXT       This vnode is a pure text prototype.
	   VSYSTEM     This vnode is being used by the kernel; only used to skip quota files in
		       vflush().
	   VISTTY      This vnode represents a tty; used when reading dead vnodes.
	   VEXECMAP    This vnode has executable mappings.
	   VWRITEMAP   This vnode might have PROT_WRITE user mappings.
	   VWRITEMAPDIRTY
		       This vnode might have dirty pages due to VWRITEMAP
	   VLOCKSWORK  This vnode's file system supports locking.
	   VXLOCK      This vnode is currently locked to change underlying type.
	   VXWANT      A process is waiting for this vnode.
	   VBWAIT      Waiting for output associated with this vnode to complete.
	   VALIASED    This vnode has an alias.
	   VDIROP      This vnode is involved in a directory operation.  This flag is used exclu-
		       sively by LFS.
	   VLAYER      This vnode is on a layered file system.
	   VONWORKLST  This vnode is on syncer work-list.
	   VFREEING    This vnode is being freed.
	   VMAPPED     This vnode might have user mappings.

     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 opera-
     tions 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 opera-
     tions vector contains a pointer to a function for each operation supported by the file sys-
     tem.  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 ref-
     erence 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:

	   VNON   The vnode has no type.
	   VREG   The vnode represents a regular file.
	   VDIR   The vnode represents a directory.
	   VBLK   The vnode represents a block special device.
	   VCHR   The vnode represents a character special device.
	   VLNK   The vnode represents a symbolic link.
	   VSOCK  The vnode represents a socket.
	   VFIFO  The vnode represents a pipe.
	   VBAD   The vnode represents a bad file (not currently used).

     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:

	   VT_NON	 non file system
	   VT_UFS	 universal file system
	   VT_NFS	 network file system
	   VT_MFS	 memory file system
	   VT_MSDOSFS	 FAT file system
	   VT_LFS	 log-structured file system
	   VT_LOFS	 loopback file system
	   VT_FDESC	 file descriptor file system
	   VT_NULL	 null file system layer
	   VT_UMAP	 uid/gid remapping file system layer
	   VT_KERNFS	 kernel interface file system
	   VT_PROCFS	 process interface file system
	   VT_AFS	 AFS file system
	   VT_ISOFS	 ISO 9660 file system(s)
	   VT_UNION	 union file system
	   VT_ADOSFS	 Amiga file system
	   VT_EXT2FS	 Linux's ext2 file system
	   VT_CODA	 Coda file system
	   VT_FILECORE	 filecore file system
	   VT_NTFS	 Microsoft NT's file system
	   VT_VFS	 virtual file system
	   VT_OVERLAY	 overlay file system
	   VT_SMBFS	 SMB file system
	   VT_PTYFS	 pseudo-terminal device file system
	   VT_TMPFS	 efficient memory file system
	   VT_UDF	 universal disk format file system
	   VT_SYSVBFS	 systemV boot file system

     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 spe-
     cific 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 invali-
     dated.  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.

FUNCTIONS
     vref(vp)
	      Increment v_usecount of the vnode vp.  Any kernel thread system which uses a vnode
	      (e.g., during the operation of some algorithm or to store in a data structure)
	      should call vref().

     vrele(vp)
	      Decrement v_usecount of unlocked vnode vp.  Any code in the system which is using a
	      vnode should call vrele() when it is finished with the vnode.  If v_usecount of the
	      vnode reaches zero and v_holdcnt is greater than zero, the vnode is placed on the
	      holdlist.  If both v_usecount and v_holdcnt are zero, the vnode is placed on the
	      freelist.

     vrele_async(vp)
	      Will asychronously release the vnode in different context than the caller, sometime
	      after the call.

     vget(vp, lockflags)
	      Reclaim vnode vp from the freelist, increment its reference count and lock it.  The
	      argument lockflags specifies the rwlock(9) flags used to lock the vnode.	If the
	      VXLOCK is set in vp's v_flag, vnode vp is being recycled in vgone() and the calling
	      thread sleeps until the transition is complete.  When it is awakened, an error is
	      returned to indicate that the vnode is no longer usable (possibly having been recy-
	      cled to a new file system type).

     vput(vp)
	      Unlock vnode vp and decrement its v_usecount.  Depending on the reference counts,
	      move the vnode to the holdlist or the freelist.  This operation is functionally
	      equivalent to calling VOP_UNLOCK(9) followed by vrele().

     vhold(vp)
	      Mark the vnode vp as active by incrementing vp->v_holdcnt and moving the vnode from
	      the freelist to the holdlist.  Once on the holdlist, the vnode will not be recycled
	      until it is released with holdrele().

     holdrele(vp)
	      Mark the vnode vp as inactive by decrementing vp->v_holdcnt and moving the vnode
	      from the holdlist to the freelist.

     getnewvnode(tag, mp, vops, slock, vpp)
	      Retrieve the next vnode from the freelist.  getnewvnode() must choose whether to
	      allocate a new vnode or recycle an existing one.	The criterion for allocating a
	      new one is that the total number of vnodes is less than the number desired or there
	      are no vnodes on either free list.  Generally only vnodes that have no buffers
	      associated with them are recycled and the next vnode from the freelist is
	      retrieved.  If the freelist is empty, vnodes on the holdlist are considered.  The
	      new vnode is returned in the address specified by vpp.

	      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.

     ungetnewvnode(vp)
	      Undo the operation of getnewvnode().  The argument vp is the vnode to return to the
	      freelist.  This function is needed for VFS_VGET(9) which may need to push back a
	      vnode in case of a locking race condition.

     vrecycle(vp, inter_lkp, l)
	      Recycle the unused vnode vp to the front of the freelist.  vrecycle() is a null
	      operation if the reference count is greater than zero.

     vgone(vp)
	      Eliminate all activity associated with the unlocked vnode vp in preparation for
	      recycling.

     vgonel(vp, p)
	      Eliminate all activity associated with the locked vnode vp in preparation for recy-
	      cling.

     vflush(mp, skipvp, flags)
	      Remove any vnodes in the vnode table belonging to mount point mp.  If skipvp is not
	      NULL it is exempt from being flushed.  The argument flags is a set of flags modify-
	      ing the operation of vflush().  If FORCECLOSE is not specified, there should not be
	      any active vnodes and the error EBUSY is returned if any are found (this is a user
	      error, not a system error).  If FORCECLOSE is specified, active vnodes that are
	      found are detached.  If WRITECLOSE is set, only flush out regular file vnodes open
	      for writing.  SKIPSYSTEM causes any vnodes marked V_SYSTEM to be skipped.

     vaccess(type, file_mode, uid, gid, acc_mode, cred)
	      Do access checking by comparing the file's permissions to the caller's desired
	      access type acc_mode and credentials cred.

     bdevvp(dev, vpp)
	      Create a vnode for a block device.  bdevvp() is used for root file systems, swap
	      areas and for memory file system special devices.

     cdevvp(dev, vpp)
	      Create a vnode for a character device.  cdevvp() is used for the console and kernfs
	      special devices.

     vfinddev(dev, vtype, vpp)
	      Lookup a vnode by device number.	The vnode is referenced and returned in the
	      address specified by vpp.

     vdevgone(int maj, int min, int minh, enum vtype type)
	      Reclaim all vnodes that correspond to the specified minor number range minl to minh
	      (endpoints inclusive) of the specified major maj.

     vwakeup(bp)
	      Update outstanding I/O count vp->v_numoutput for the vnode bp->b_vp and do a wakeup
	      if requested and vp->vflag has VBWAIT set.

     vflushbuf(vp, sync)
	      Flush all dirty buffers to disk for the file with the locked vnode vp.  The argu-
	      ment sync specifies whether the I/O should be synchronous and vflushbuf() will
	      sleep until vp->v_numoutput is zero and vp->v_dirtyblkhd is empty.

     vinvalbuf(vp, flags, cred, l, slpflag, slptimeo)
	      Flush out and invalidate all buffers associated with locked vnode vp.  The argument
	      l and cred specified the calling process and its credentials.  The ltsleep(9) flag
	      and timeout are specified by the arguments slpflag and slptimeo respectively.  If
	      the operation is successful zero is returned, otherwise an appropriate error code
	      is returned.

     vtruncbuf(vp, lbn, slpflag, slptimeo)
	      Destroy any in-core buffers past the file truncation length for the locked vnode
	      vp.  The truncation length is specified by lbn.  vtruncbuf() will sleep while the
	      I/O is performed,  The ltsleep(9) flag and timeout are specified by the arguments
	      slpflag and slptimeo respectively.  If the operation is successful zero is
	      returned, otherwise an appropriate error code is returned.

     vprint(label, vp)
	      This function is used by the kernel to dump vnode information during a panic.  It
	      is only used if the kernel option DIAGNOSTIC is compiled into the kernel.  The
	      argument label is a string to prefix the information dump of vnode vp.

CODE REFERENCES
     The vnode framework is implemented within the file sys/kern/vfs_subr.c.

SEE ALSO
     intro(9), lock(9), namecache(9), namei(9), uvm(9), vattr(9), vfs(9), vfsops(9), vnodeops(9),
     vnsubr(9)

BUGS
     The locking protocol is inconsistent.  Many vnode operations are passed locked vnodes on
     entry but release the lock before they exit.  The locking protocol is used in some places to
     attempt to make a series of operations atomic (e.g., access check then operation).  This
     does not work for non-local file systems that do not support locking (e.g., NFS).	The vnode
     interface would benefit from a simpler locking protocol.

BSD					 February 8, 2012				      BSD


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