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 #ifndef __SFS_XIO_H__
 #define __SFS_XIO_H__
 /******************************************************************************/
 /*                                                                            */
 /*                          X r d S f s X i o . h h                           */
 /*                                                                            */
 /* (c) 2013 by the Board of Trustees of the Leland Stanford, Jr., University  */
 /*   Produced by Andrew Hanushevsky for Stanford University under contract    */
 /*              DE-AC02-76-SFO0515 with the Department of Energy              */
 /*                                                                            */
 /* This file is part of the XRootD software suite.                            */
 /*                                                                            */
 /* XRootD is free software: you can redistribute it and/or modify it under    */
 /* the terms of the GNU Lesser General Public License as published by the     */
 /* Free Software Foundation, either version 3 of the License, or (at your     */
 /* option) any later version.                                                 */
 /*                                                                            */
 /* XRootD is distributed in the hope that it will be useful, but WITHOUT      */
 /* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or      */
 /* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public       */
 /* License for more details.                                                  */
 /*                                                                            */
 /* You should have received a copy of the GNU Lesser General Public License   */
 /* along with XRootD in a file called COPYING.LESSER (LGPL license) and file  */
 /* COPYING (GPL license).  If not, see <http://www.gnu.org/licenses/>.        */
 /*                                                                            */
 /* The copyright holder's institutional names and contributor's names may not */
 /* be used to endorse or promote products derived from this software without  */
 /* specific prior written permission of the institution or contributor.       */
 /******************************************************************************/
 
 //-----------------------------------------------------------------------------
 //! XrdSfsXio.hh
 //!
 //! This class is used to allow file I/O interfaces to perform exchange buffer
 //! I/O in order to minimize data copying. When this feature is enabled, the
 //! XrdSfsInterface::setXio() method is called on a newly created XrdSfsFile
 //! object. Ideally, all oustanding buffers should be be released when the file
 //! is closed. Alternatively, the XrdSfsXio::Reclaim() method may be used
 //! at any time when it is convenient to do so. For best performance, use
 //! XrdSfsXio::Swap() as it provides memory locality and is kind to the cache.
 //! Buffer swapping is only supported for common file write operations.
 //-----------------------------------------------------------------------------
 
 //typedef void* XrdSfsXioHandle;
 typedef class XrdBuffer* XrdSfsXioHandle;
 
 class XrdSfsXioImpl;
 
 /******************************************************************************/
 /*                       C l a s s   X r d S f s X i o                        */
 /******************************************************************************/
   
 class XrdSfsXio
 {
 public:
 
 //-----------------------------------------------------------------------------
 //! Get the address and size of the buffer associated with a handle.
 //!
 //! @param theHand  - The handle associated with the buffer.
 //! @param buffsz   - If not nil, the size of the buffer is returned. The
 //!                   size will always be >= to the original data length.
 //!
 //! @return A pointer to the buffer.
 //-----------------------------------------------------------------------------
 
 static char      *Buffer(XrdSfsXioHandle theHand, int *buffsz=0);
 
 //-----------------------------------------------------------------------------
 //! Claim ownership of the current buffer if it is memory effecient to do so.
 //!
 //! @param  curBuff - The address of the current buffer. It must match the
 //!                   the buffer that was most recently passed to the caller.
 //! @param  datasz  - Number of useful bytes in the buffer (i.e. write size).
 //! @param  minasz  - Minimum buffer size that would be allocated to copy data.
 //!
 //! @return !0        The buffer handle of the current buffer is returned along
 //!                   with ownership rights.
 //! @return =0        Too much memory would be wasted by transferring ownership
 //!                   (errno == 0) or an error ocurred (errno != 0). When an
 //!                   error see Swap() below for possible types of errors.
 //-----------------------------------------------------------------------------
 virtual
 XrdSfsXioHandle   Claim(const char *curBuff, int datasz, int minasz) = 0;
 
 //-----------------------------------------------------------------------------
 //! Return a buffer previously gotten from a Claim() or Swap() call.
 //!
 //! @param theHand  - The handle associated with the buffer.
 //-----------------------------------------------------------------------------
 
 static void       Reclaim(XrdSfsXioHandle theHand);
 
 //-----------------------------------------------------------------------------
 //! Swap the current I/O buffer
 //!
 //! @param  curBuff - The address of the current buffer. It must match the
 //!                   the buffer that was most recently passed to the caller.
 //! @param  oldHand - The handle associated with a buffer returned by a
 //!                   previous call to Swap(). A value of zero indicates that
 //!                   the caller is taking control of the buffer but has no
 //!                   replacement buffer.
 //! @return !0        The buffer handle of the current buffer is returned along
 //!                   with ownership rights. If oldHand was not nil, the
 //!                   caller's ownership of the associated buffer is reclaimed.
 //! @return =0        An error occurred and nothing has changed; errno holds
 //!                   the reason for the error. Typically,
 //!                   EINVAL  - curBuff doe not match current buffer.
 //!                   ENOBUFS - not enough memory to give up buffer.
 //!                   ENOTSUP - unsupported context for call.
 //-----------------------------------------------------------------------------
 virtual
 XrdSfsXioHandle   Swap(const char *curBuff, XrdSfsXioHandle oldHand=0) = 0;
 
 //-----------------------------------------------------------------------------
 //! Constructor and destructor
 //!
 //! @param xioimpl    Reference to static method implementations.
 //-----------------------------------------------------------------------------
 
              XrdSfsXio(XrdSfsXioImpl &xioimpl);
 
 //-----------------------------------------------------------------------------
 //! Constructor and destructor
 //-----------------------------------------------------------------------------
 
 virtual     ~XrdSfsXio() {}
 };
 #endif

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