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NAME    [Toc]    [Back]

     vn_lock - acquire the vnode lock

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <sys/vnode.h>

     vn_lock(struct vnode *vp, int flags, struct proc *p);

DESCRIPTION    [Toc]    [Back]

     The vn_lock() function is used to acquire  the  vnode  lock.
Certain file
     system  operations  require that the vnode lock be held when
they are
     called.  See sys/kern/vnode_if.src for more details.

     The vn_lock() function must not be called when  the  vnode's
     count is zero.  Instead, the vget() function should be used.

     The flags argument may contain the following flags:

           LK_RETRY        Return the vnode even if it  has  been
           LK_INTERLOCK    Must be set if the caller owns the vnode interlock.
           LK_NOWAIT       Don't wait if the vnode lock  is  held
by someone
                           else  (may  still  wait on reclamation
lock on or interlock).
   Must  not  be  used   with
           LK_EXCLUSIVE    Acquire an exclusive lock.
           LK_SHARED       Acquire a shared lock.

     The  vn_lock()  function  can sleep.  The vn_lock() releases
the vnode interlock
 before exit.

RETURN VALUES    [Toc]    [Back]

     Upon successful completion, a value of 0 is returned.   Otherwise, one of
     the following errors is returned.

ERRORS    [Toc]    [Back]

     [ENOENT]       The  vnode  has  been  reclaimed and is dead.
This error is
                   only returned if  the  LK_RETRY  flag  is  not

     [EBUSY]       The LK_NOWAIT flag was set and vn_lock() would
have slept.

SEE ALSO    [Toc]    [Back]


BUGS    [Toc]    [Back]

     The locking discipline is bizarre.   Many  vnode  operations
are passed
     locked  vnodes on entry but release the lock before they exit.  Discussions
 with Kirk McKusick indicate  that  locking  discipline
evolved out of
     the  pre-VFS  way  of doing inode locking.  In addition, the
current locking
     discipline may actually save lines of code, esp. if the number of file
     systems  is  fewer  than the number of call sites.  However,
the VFS interface
 would require less wizardry if the  locking  discipline
were simpler.

     The  locking discipline is used in some places to attempt to
make a series
     of operations atomic (e.g., permissions check +  operation).
This does
     not  work  for  non-local  file  systems that do not support
locking (e.g.,

     Are vnode locks even necessary?  The security checks can  be
moved into
     the  individual file systems.  Each file system can have the
 of ensuring that vnode operations are suitably atomic.

     The LK_NOWAIT flag does prevent the caller from sleeping.

     The locking discipline as it relates to shared locks has yet
to be defined.

OpenBSD      3.6                           March      9,     2001
[ Back ]
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