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CentOS 7.0 - man page for dlm_ls_lockx (centos section 3)

DLM_LOCK(3)			     Library Functions Manual			      DLM_LOCK(3)

       dlm_lock - acquire or convert a DLM lock

	#include <libdlm.h>

       int dlm_lock(uint32_t mode,
		 struct dlm_lksb *lksb,
		 uint32_t flags,
		 const void *name,
		 unsigned int namelen,
		 uint32_t parent,	  /* unused */
		 void (*astaddr) (void *astarg),
		 void *astarg,
		 void (*bastaddr) (void *astarg),
		 void *range);		  /* unused */

       int dlm_lock_wait(uint32_t mode,
		 struct dlm_lksb *lksb,
		 uint32_t flags,
		 const void *name,
		 unsigned int namelen,
		 uint32_t parent,	  /* unused */
		 void *bastarg,
		 void (*bastaddr) (void *bastarg),
		 void *range);		  /* unused */

       int dlm_ls_lock(dlm_lshandle_t lockspace,
		 uint32_t mode,
		 struct dlm_lksb *lksb,
		 uint32_t flags,
		 const void *name,
		 unsigned int namelen,
		 uint32_t parent,	  /* unused */
		 void (*astaddr) (void *astarg),
		 void *astarg,
		 void (*bastaddr) (void *astarg),
		 void *range);		  /* unused */

       int dlm_ls_lock_wait(dlm_lshandle_t lockspace,
		 uint32_t mode,
		 struct dlm_lksb *lksb,
		 uint32_t flags,
		 const void *name,
		 unsigned int namelen,
		 uint32_t parent,	  /* unusued */
		 void *bastarg,
		 void (*bastaddr) (void *bastarg),
		 void *range);		  /* unused */

       int dlm_ls_lockx(dlm_lshandle_t lockspace,
		 uint32_t mode,
		 struct dlm_lksb *lksb,
		 uint32_t flags,
		 const void *name,
		 unsigned int namelen,
		 uint32_t parent,	  /* unused */
		 (*astaddr) (void *astarg),
		 void *astarg,
		 void (*bastaddr) (void *astarg),
		 uint64_t *xid,
		 uint64_t *timeout);

       dlm_lock and its variants acquire and convert locks in the DLM.

       dlm_lock()  operations are asynchronous. If the call to dlm_lock returns an error then the
       operation has failed and the AST routine will not be called. If dlm_lock returns 0  it  is
       still  possible that the lock operation will fail. The AST routine will be called when the
       locking is complete or has failed and the status is returned in the lksb.  dlm_lock_wait()
       will  wait until the lock operation has completed and returns the final completion status.
       dlm_ls_lock() is the same as dlm_lock() but takes a  lockspace  argument.  This	lockspace
       must have been previously opened by dlm_lockspace_open() or dlm_lockspace_create().

       For  conversion operations the name and namelen are ignored and the lock ID in the LKSB is
       used to identify the lock to be converted.

       If a lock value block is specified then in general, a grant or a conversion to  an  equal-
       level  or  higher-level lock mode reads the lock value from the resource into the caller's
       lock value block. When a lock conversion from EX or PW to an  equal-level  or  lower-level
       lock  mode  occurs,  the  contents  of  the caller's lock value block are written into the
       resource. If the LVB is invalidated the lksb.sb_flags member will be set  to  DLM_SBF_VAL-
       NOTVALID. Lock values blocks are always 32 bytes long.

       If the AST routines or parameter are passed to a conversion operation then they will over-
       write those values that were passed to a previous dlm_lock call.

       mode Lock mode to acquire or convert to.
	 LKM_CRMODE   Concurrent read
	 LKM_CWMODE   Concurrent write
	 LKM_PRMODE   Protected read
	 LKM_PWMODE   Protected write
	 LKM_EXMODE   Exclusive

       flags Affect the operation of the lock call:
	 LKF_NOQUEUE	 Don't queue the lock. If it cannot be granted return
	 LKF_CONVERT	 Convert an existing lock
	 LKF_VALBLK	 Lock has a value block
	 LKF_QUECVT	 Put conversion to the back of the queue
	 LKF_EXPEDITE	 Grant a NL lock immediately regardless of other locks
			 on the conversion queue
	 LKF_PERSISTENT  Specifies a lock that will not be unlocked when the
			 process exits; it will become an orphan lock.
	 LKF_CONVDEADLK  Enable internal conversion deadlock resolution where
			 the lock's granted mode may be set to NL and
			 DLM_SBF_DEMOTED is returned in lksb.sb_flags.
	 LKF_NODLCKWT	 Do not consider this lock when trying to detect
			 deadlock conditions.
	 LKF_NODLCKBLK	 Not implemented
	 LKF_NOQUEUEBAST Send blocking ASTs even for NOQUEUE operations
	 LKF_HEADQUE	 Add locks to the head of the convert or waiting queue
	 LKF_NOORDER	 Avoid the VMS rules on grant order
	 LKF_ALTPR	 If the requested mode can't be granted (generally CW),
			 try to grant in PR and return DLM_SBF_ALTMODE.
	 LKF_ALTCW	 If the requested mode can't be granted (generally PR),
			 try to grant in CW and return DLM_SBF_ALTMODE.
	 LKF_TIMEOUT	 The lock will time out per the timeout arg.

       lksb Lock Status block
       This structure contains the returned lock ID, the actual status of the lock operation (all
       lock ops are asynchronous) and the value block if LKF_VALBLK is set.

       Name of the lock. Can be binary, max 64 bytes. Ignored for lock conversions.  (Should be a
       string to work with debugging tools.)

       Length of the above name. Ignored for lock conversions.

       ID of parent lock or NULL if this is a top-level lock. This is currently unused.

       Address of AST routine to be called when the lock operation completes. The  final  comple-
       tion status of the lock will be in the lksb. the AST routine must not be NULL.

       Argument  to pass to the AST routine (most people pass the lksb in here but it can be any-
       thing you like.)

       Blocking AST routine. address of a function to call if this lock is blocking another.  The
       function will be called with astargs.

       This is unused.

       Optional transaction ID for deadlock detection.

       Timeout in centiseconds. If it takes longer than this to acquire the lock (usually because
       it is already blocked by another lock), then the AST will trigger with  ETIMEDOUT  as  the
       status.	If  the  lock  operation is a conversion then the lock will remain at its current
       status. If this is a new lock then the lock will not exist and any LKB in the lksb will be
       invalid.  This is ignored without the LKF_TIMEOUT flag.

   Return values
       0  is returned if the call completed successfully. If not, -1 is returned and errno is set
       to one of the following:

       EINVAL	       An invalid parameter was passed to the call (eg bad lock
		       mode or flag)
       ENOMEM	       A (kernel) memory allocation failed
       EAGAIN	       LKF_NOQUEUE was requested and the lock could not be
       EBUSY	       The lock is currently being locked or converted
       EFAULT	       The userland buffer could not be read/written by the
		       kernel (this indicates a library problem)
       EDEADLOCK       The lock operation is causing a deadlock and has been
		       cancelled. If this was a conversion then the lock is
		       reverted to its previously granted state. If it was a
		       new lock then it has not been granted. (NB Only
		       conversion deadlocks are currently detected)

       If an error is returned in the AST, then lksb.sb_status is set to the one of the above values instead of zero.

       struct dlm_lksb {
	 int	  sb_status; /* Final status of lock operation */
	 uint32_t sb_lkid;   /* ID of lock. Returned from dlm_lock()
				on first use. Used as input to
				dlm_lock() for a conversion operation */
	 char	  sb_flags;  /* Completion flags, see above */
	 char	  sb_lvbptr; /* Optional pointer to lock value block */

       int status;
       struct dlm_lksb lksb;

       status = dlm_lock_wait(LKM_EXMODE,
			      0, // Parent,
			      NULL, // bast arg
			      NULL, // bast routine,
			      NULL); // Range

       if (status == 0)
	    dlm_unlock_wait(lksb.sb_lkid, 0, &lksb);

       libdlm(3),      dlm_unlock(3),	    dlm_open_lockspace(3),	 dlm_create_lockspace(3),
       dlm_close_lockspace(3), dlm_release_lockspace(3)

libdlm functions			   July 5, 2007 			      DLM_LOCK(3)

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