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

NAME
     vnode, vref, vrele, vrele_async, vput, vhold, holdrele, vcache_get,
     vcache_new, vcache_rekey_enter, vcache_rekey_exit, vrecycle, vgone,
     vgonel, vdead_check, 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);

     void
     vput(struct vnode *vp);

     void
     vhold(struct vnode *vp);

     void
     holdrele(struct vnode *vp);

     int
     vcache_get(struct mount *mp, const void *key, size_t key_len,
         struct vnode **vpp);

     int
     vcache_new(struct mount *mp, struct vnode *dvp, struct vattr *vap,
         kauth_cred_t cred, void *extra, struct vnode **vpp);

     int
     vcache_rekey_enter(struct mount *mp, struct vnode *vp,
         const void *old_key, size_t old_key_len, const void *new_key,
         size_t new_key_len);

     void
     vcache_rekey_exit(struct mount *mp, struct vnode *vp,
         const void *old_key, size_t old_key_len, const void *new_key,
         size_t new_key_len);

     int
     vrecycle(struct vnode *vp);

     void
     vgone(struct vnode *vp);

     void
     vgonel(struct vnode *vp, struct lwp *l);

     int
     vdead_check(struct vnode *vp, int flags);

     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
     A vnode represents an on-disk file in use by the system.  Each vfs(9)
     file system provides a set of vnodeops(9) operations on vnodes, invoked
     by file-system-independent system calls and supported by file-system-
     independent library routines.

     Each mounted file system provides a vnode for the root of the file
     system, via VFS_ROOT(9).  Other vnodes are obtained by VOP_LOOKUP(9).
     Users of vnodes usually invoke these indirectly via namei(9) to obtain
     vnodes from paths.

     Each file system usually maintains a cache mapping recently used inode
     numbers, or the equivalent, to vnodes, and a cache mapping recently used
     file names to vnodes.  If memory is scarce, the system may decide to
     reclaim an unused cached vnode, calling VOP_RECLAIM(9) to remove it from
     the caches and to free file-system-specific memory associated with it.  A
     file system may also choose to immediately reclaim a cached vnode once it
     is unused, in VOP_INACTIVE(9), if the vnode has been deleted on disk.

     When a file system retrieves a vnode from a cache, the vnode may not have
     any users, and another thread in the system may be simultaneously
     deciding to reclaim it.  Thus, to retrieve a vnode from a cache, one must
     use vcache_get(), not vref(), to acquire the first reference.

     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 */
             struct mount    *v_mount;               /* ptr to vfs we are in */
             int             (**v_op)(void *);       /* vnode operations vector */
             struct buflists v_cleanblkhd;           /* clean blocklist head */
             struct buflists v_dirtyblkhd;           /* dirty blocklist head */
             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 */
             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_iflag, v_vflag and v_uflag.  Valid flags
     are:

           VV_ROOT            This vnode is the root of its file system.
           VV_SYSTEM          This vnode is being used by the kernel; only
                              used to skip quota files in vflush().
           VV_ISTTY           This vnode represents a tty; used when reading
                              dead vnodes.
           VV_MAPPED          This vnode might have user mappings.
           VV_MPSAFE          This file system is MP safe.
           VV_LOCKSWORK       This vnode's file system supports locking.
           VI_TEXT            This vnode is a pure text prototype.
           VI_EXECMAP         This vnode has executable mappings.
           VI_WRMAP           This vnode might have PROT_WRITE user mappings.
           VI_WRMAPDIRTY      This vnode might have dirty pages due to
                              VWRITEMAP.
           VI_XLOCK           This vnode is currently locked to change
                              underlying type.
           VI_ONWORKLST       This vnode is on syncer work-list.
           VI_MARKER          A dummy marker vnode.
           VI_CLEAN           This vnode has been reclaimed and is no longer
                              attached to a file system.
           VU_DIROP           This vnode is involved in a directory operation.
                              This flag is used exclusively by LFS.

     The VI_XLOCK 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.  Before v_iflag can be modified, the
     v_interlock mutex 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 cached.  The transition from the cache is handled by a kernel thread
     and vrecycle().  Access to v_usecount, v_writecount and v_holdcnt is also
     protected by the v_interlock mutex.

     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.

     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 a user wants a new vnode for another file or wants a valid vnode
     which is cached, vcache_get() or vcache_new() is invoked to allocate a
     vnode 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

     The vnode 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 vnode 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, and v_cleanblkhd 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 cached.

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

     vput(vp)
              Legacy convenience routine for unlocking and releasing vp.
              Equivalent to:

                  VOP_UNLOCK(vp);
                  vrele(vp);

              New code should prefer using VOP_UNLOCK(9) and vrele() directly.

     vhold(vp)
              Mark the vnode vp as active by incrementing vp->v_holdcnt.  Once
              held, 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.

     vcache_get(mp, key, key_len, vpp)
              Allocate a new vnode.  The new vnode is returned referenced in
              the address specified by vpp.

              The argument mp is the mount point for the file system to lookup
              the file in.

              The arguments key and key_len uniquely identify the file in the
              file system.

              If a vnode is successfully retrieved zero is returned, otherwise
              an appropriate error code is returned.

     vcache_new(mp, dvp, vap, cred, vpp)
              Allocate a new vnode with a new file.  The new vnode is returned
              referenced in the address specified by vpp.

              The argument mp is the mount point for the file system to create
              the file in.

              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.

              If a vnode is successfully created zero is returned, otherwise
              an appropriate error code is returned.

     vcache_rekey_enter(mp, vp, old_key, old_key_len, new_key, new_key_len)
              Prepare to change the key of a cached vnode.

              The argument mp is the mount point for the file system the vnode
              vp resides in.

              The arguments old_key and old_key_len identify the cached vnode.

              The arguments new_key and new_key_len will identify the vnode
              after rename.

              If the new key already exists EEXIST is returned, otherwise zero
              is returned.

     vcache_rekey_exit(mp, vp, old_key, old_key_len, new_key, new_key_len)
              Finish rename after calling vcache_rekey_enter().

     vrecycle(vp)
              Recycle the referenced vnode vp if this is the last reference.
              vrecycle() is a null operation if the reference count is greater
              than one.

     vgone(vp)
              Eliminate all activity associated with the unlocked vnode vp in
              preparation for recycling.  This operation is restricted to
              suspended file systems.  See vfs_suspend(9).

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

     vdead_check(vp, flags)
              Check the vnode vp for being or becoming dead.  Returns ENOENT
              for a dead vnode and zero otherwise.  If flags is VDEAD_NOWAIT
              it will return EBUSY if the vnode is becoming dead and the
              function will not sleep.

              Whenever this function returns a non-zero value all future calls
              for this vp will also return a non-zero value.

     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 modifying 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 argument 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.

NetBSD 8.99.34                  January 1, 2019                 NetBSD 8.99.34