XrdSsiFileSess.cc

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/******************************************************************************/
/*                                                                            */
/*                     X r d S s i F i l e S e s s . c c                      */
/*                                                                            */
/* (c) 2016 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.       */
/******************************************************************************/
 
#include <fcntl.h>
#include <stddef.h>
#include <cstdio>
#include <cstring>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/uio.h>
 
#include "XrdNet/XrdNetAddrInfo.hh"
 
#include "XrdOuc/XrdOucBuffer.hh"
#include "XrdOuc/XrdOucEnv.hh"
#include "XrdOuc/XrdOucERoute.hh"
#include "XrdOuc/XrdOucPList.hh"
 
#include "XrdSec/XrdSecEntity.hh"
 
#include "XrdSfs/XrdSfsAio.hh"
 
#include "XrdSsi/XrdSsiEntity.hh"
#include "XrdSsi/XrdSsiFileSess.hh"
#include "XrdSsi/XrdSsiProvider.hh"
#include "XrdSsi/XrdSsiRRInfo.hh"
#include "XrdSsi/XrdSsiService.hh"
#include "XrdSsi/XrdSsiSfs.hh"
#include "XrdSsi/XrdSsiStats.hh"
#include "XrdSsi/XrdSsiStream.hh"
#include "XrdSsi/XrdSsiTrace.hh"
#include "XrdSsi/XrdSsiUtils.hh"
 
#include "XrdSys/XrdSysE2T.hh"
#include "XrdSys/XrdSysError.hh"
  
/******************************************************************************/
/*                               G l o b a l s                                */
/******************************************************************************/
 
namespace XrdSsi
{
extern XrdOucBuffPool   *BuffPool;
extern XrdSsiProvider   *Provider;
extern XrdSsiService    *Service;
extern XrdSsiStats       Stats;
extern XrdSysError       Log;
extern int               respWT;
extern int               minRSZ;
extern int               maxRSZ;
}
 
using namespace XrdSsi;
 
/******************************************************************************/
/*                          L o c a l   M a c r o s                           */
/******************************************************************************/
 
#define DUMPIT(x,y) XrdSsiUtils::b2x(x,y,hexBuff,sizeof(hexBuff),dotBuff)<<dotBuff
 
/******************************************************************************/
/*                         L o c a l   C l a s s e s                          */
/******************************************************************************/
  
namespace
{
class nullCallBack : public XrdOucEICB
{
public:
 
void     Done(int &Result, XrdOucErrInfo *eInfo, const char *Path=0) {}
 
int      Same(unsigned long long arg1, unsigned long long arg2) {return 0;}
 
         nullCallBack() {}
virtual ~nullCallBack() {}
};
 
nullCallBack nullCB;
};
  
/******************************************************************************/
/*                        S t a t i c   M e m b e r s                         */
/******************************************************************************/
 
XrdSysMutex     XrdSsiFileSess::arMutex;
XrdSsiFileSess *XrdSsiFileSess::freeList = 0;
int             XrdSsiFileSess::freeNum  = 0;
int             XrdSsiFileSess::freeNew  = 0;
int             XrdSsiFileSess::freeMax  = 100;
int             XrdSsiFileSess::freeAbs  = 200;
 
bool            XrdSsiFileSess::authDNS  = false;
 
/******************************************************************************/
/*                                 A l l o c                                  */
/******************************************************************************/
  
XrdSsiFileSess *XrdSsiFileSess::Alloc(XrdOucErrInfo &einfo, const char *user)
{
   XrdSsiFileSess *fsP;
 
// Get a lock
//
   arMutex.Lock();
 
// Get either a reuseable object or a new one
//
   if ((fsP = freeList))
      {freeNum--;
       freeList = fsP->nextFree;
       arMutex.UnLock();
       fsP->Init(einfo, user, true);
      } else {
       freeNew++;
       if (freeMax <= freeAbs && freeNew >= freeMax/2)
          {freeMax += freeMax/2;
           freeNew = 0;
          }
       arMutex.UnLock();
       fsP = new XrdSsiFileSess(einfo, user);
      }
 
// Return the object
//
   return fsP;
}
 
/******************************************************************************/
/*                              A t t n I n f o                               */
/******************************************************************************/
  
bool XrdSsiFileSess::AttnInfo(XrdOucErrInfo &eInfo, const XrdSsiRespInfo *respP,
                              unsigned int reqID)
// Called with the request mutex locked!
{
   EPNAME("AttnInfo");
   struct AttnResp {struct iovec ioV[4]; XrdSsiRRInfoAttn aHdr;};
 
   AttnResp *attnResp;
   char *mBuff;
   int n, ioN = 2;
   bool doFin;
 
// If there is no data we can send back to the client in the attn response,
// then simply reply with a short message to make the client come back.
//
   if (!respP->mdlen)
      {if (respP->rType != XrdSsiRespInfo::isData
       ||  respP->blen > XrdSsiResponder::MaxDirectXfr)
          {eInfo.setErrInfo(0, "");
           return false;
          }
      }
 
// We will be constructing the response in the message buffer. This is
// gauranteed to be big enough for our purposes so no need to check the size.
//
   mBuff = eInfo.getMsgBuff(n);
 
// Initialize the response
//
   attnResp = (AttnResp *)mBuff;
   memset(attnResp, 0, sizeof(AttnResp));
   attnResp->aHdr.pfxLen = htons(sizeof(XrdSsiRRInfoAttn));
 
// Fill out iovec to point to our header
//
//?attnResp->ioV[0].iov_len  = sizeof(XrdSsiRRInfoAttn) + respP->mdlen;
   attnResp->ioV[1].iov_base = mBuff+offsetof(struct AttnResp, aHdr);
   attnResp->ioV[1].iov_len  = sizeof(XrdSsiRRInfoAttn);
 
// Fill out the iovec for the metadata if we have some
//
   if (respP->mdlen)
      {attnResp->ioV[2].iov_base = (void *)respP->mdata;
       attnResp->ioV[2].iov_len  =         respP->mdlen; ioN = 3;
       attnResp->aHdr.mdLen = htonl(respP->mdlen);
       Stats.Bump(Stats.RspMDBytes, respP->mdlen);
       if (QTRACE(Debug))
          {char hexBuff[16],dotBuff[4];
           DEBUG(reqID <<':' <<gigID <<' ' <<respP->mdlen <<" byte metadata (0x"
                       <<DUMPIT(respP->mdata,respP->mdlen) <<") sent.");
          }
      }
 
// Check if we have actual data here as well and can send it along
//
   if (respP->rType == XrdSsiRespInfo::isData
   &&  respP->blen+respP->mdlen <= XrdSsiResponder::MaxDirectXfr)
      {if (respP->blen)
          {attnResp->ioV[ioN].iov_base = (void *)respP->buff;
           attnResp->ioV[ioN].iov_len  =         respP->blen; ioN++;
          }
         attnResp->aHdr.tag = XrdSsiRRInfoAttn::fullResp; doFin = true;
      }
   else {attnResp->aHdr.tag = XrdSsiRRInfoAttn::pendResp; doFin = false;}
 
// If we sent the full response we must remove the request from the request
// table as it will get finished off when the response is actually sent.
//
   if (doFin)
     {XrdSsiRRTableItem<XrdSsiFileReq> rqstP;
      if (!(rqstP = rTab.LookUp(reqID)))
        {eInfo.setErrInfo(0, "");
         return false;
        }
      attnFinCallBack.setReq(std::move(rqstP));
      eInfo.setErrCB(&attnFinCallBack);
      rTab.Del(reqID);
     }
 
// Setup to have metadata actually sent to the requestor
//
   eInfo.setErrCode(ioN);
   return doFin;
}
  
/******************************************************************************/
/*                                 c l o s e                                  */
/******************************************************************************/
 
int XrdSsiFileSess::close(bool viaDel)
/*
  Function: Close the file object.
 
  Input:    None
 
  Output:   Always returns SFS_OK
*/
{
   const char *epname = "close";
 
// Do some debugging
//
   DEBUG((gigID ? gigID : "???") <<" del=" <<viaDel);
 
// Collect statistics if this is a delete which implies a lost connection
//
   if (viaDel)
      {int rCnt = rTab.Num();
       if (rCnt) Stats.Bump(Stats.ReqFinForce, rCnt);
      }
 
// Run through all outstanding requests and comlete them
//
   rTab.Reset();
 
// Free any in-progress buffers
//
   if (inProg)
      {if (oucBuff) {oucBuff->Recycle(); oucBuff = 0;}
       inProg = false;
      }
 
// Clean up storage
//
   isOpen = false;
   return SFS_OK;
}
  
/******************************************************************************/
/*                                  f c t l                                   */
/******************************************************************************/
 
int XrdSsiFileSess::fctl(const int           cmd,
                               int           alen,
                         const char         *args,
                         const XrdSecEntity *client)
{
   static const char *epname = "fctl";
   XrdSsiRRInfo      *rInfo;
   XrdSsiRRTableItem<XrdSsiFileReq> rqstP;
   unsigned int       reqID;
 
// If this isn't the special query, then return an error
//
   if (cmd != SFS_FCTL_SPEC1)
      return XrdSsiUtils::Emsg(epname, ENOTSUP, "fctl", gigID, *eInfo);
 
// Caller wishes to find out if a request is ready and wait if it is not
//
   if (!args || alen < (int)sizeof(XrdSsiRRInfo))
      return XrdSsiUtils::Emsg(epname, EINVAL, "fctl", gigID, *eInfo);
 
// Grab the request identifier
//
   rInfo = (XrdSsiRRInfo *)args;
   reqID = rInfo->Id();
 
// Do some debugging
//
   DEBUG(reqID <<':' <<gigID <<" query resp status");
 
// Find the request
//
   if (!(rqstP = rTab.LookUp(reqID)))
      return XrdSsiUtils::Emsg(epname, ESRCH, "fctl", gigID, *eInfo);
 
// Check if a response is waiting for the caller
//
   if (rqstP->WantResponse(*eInfo))
      {DEBUG(reqID <<':' <<gigID <<" resp ready");
       Stats.Bump(Stats.RspReady);
       return SFS_DATAVEC;
      }
 
// Put this client into callback state
//
   DEBUG(reqID <<':' <<gigID <<" resp not ready");
   fctlCallBack.setReq(std::move(rqstP));
 
   eInfo->setErrCB(&fctlCallBack);
   eInfo->setErrInfo(respWT, "");
   Stats.Bump(Stats.RspUnRdy);
   return SFS_STARTED;
}
 
/******************************************************************************/
/* Private:                         I n i t                                   */
/******************************************************************************/
 
void XrdSsiFileSess::Init(XrdOucErrInfo &einfo, const char *user, bool forReuse)
{
   tident     = (user ? strdup(user) : strdup(""));
   eInfo      = &einfo;
   gigID      = 0;
   fsUser     = 0;
   xioP       = 0;
   oucBuff    = 0;
   reqSize    = 0;
   reqLeft    = 0;
   isOpen     = false;
   inProg     = false;
   if (forReuse)
      {eofVec.Reset();
       rTab.Clear();
      }
}
  
/******************************************************************************/
/* Private:                   N e w R e q u e s t                             */
/******************************************************************************/
  
bool XrdSsiFileSess::NewRequest(unsigned int     reqid,
                                XrdOucBuffer    *oP,
                                XrdSfsXioHandle  bR,
                                int              rSz)
{
   XrdSsiFileReq *reqP;
 
// Allocate a new request object
//
   if (!(reqP=XrdSsiFileReq::Alloc(eInfo,&fileResource,this,gigID,tident,reqid)))
      return false;
 
// Add it to the table
//
   XrdSsiRRTableItem<XrdSsiFileReq> rqstP = rTab.Add(reqP, reqid);
   if (!rqstP)
      {delete reqP;
       return false;
      }
 
// Activate the request
//
   inProg = false;
   rqstP->Activate(oP, bR, rSz);
   return true;
}
  
/******************************************************************************/
/*                                  o p e n                                   */
/******************************************************************************/
 
int XrdSsiFileSess::open(const char         *path,      // In
                         XrdOucEnv          &theEnv,    // In
                         XrdSfsFileOpenMode  open_mode) // In
/*
  Function: Open the file `path' in the mode indicated by `open_mode'.  
 
  Input:    path      - The fully qualified name of the resource.
            theEnv    - Environmental information.
            open_mode - It must contain only SFS_O_RDWR.
 
  Output:   Returns SFS_OK upon success, otherwise SFS_ERROR is returned.
*/
{
   static const char *epname = "open";
   XrdSsiErrInfo errInfo;
   const char *eText;
   int eNum;
 
// Verify that this object is not already associated with an open file
//
   if (isOpen)
      return XrdSsiUtils::Emsg(epname, EADDRINUSE, "open session", path, *eInfo);
 
// Make sure the open flag is correct (we now open this R/O so don't check)
//
// if (open_mode != SFS_O_RDWR)
//    return XrdSsiUtils::Emsg(epname, EPROTOTYPE, "open session", path, *eInfo);
 
// Setup the file resource object
//
   fileResource.Init(path, theEnv, authDNS);
 
// Notify the provider that we will be executing a request
//
   if (Service->Prepare(errInfo, fileResource))
      {const char *usr = fileResource.rUser.c_str();
       if (!(*usr)) gigID = strdup(path);
          else {char gBuff[2048];
                snprintf(gBuff, sizeof(gBuff), "%s:%s", usr, path);
                gigID = strdup(gBuff);
               }
       DEBUG(gigID <<" prepared.");
       isOpen = true;
       return SFS_OK;
      }
 
// Get error information
//
   eText = errInfo.Get(eNum).c_str();
   if (!eNum)
      {eNum = ENOMSG; eText = "Provider returned invalid prepare response.";}
 
// Decode the error
//
   switch(eNum)
         {case EAGAIN:
               if (!eText || !(*eText)) break;
               eNum = errInfo.GetArg();
               DEBUG(path <<" --> " <<eText <<':' <<eNum);
               eInfo->setErrInfo(eNum, eText);
               Stats.Bump(Stats.ReqRedir);
               return SFS_REDIRECT;
               break;
          case EBUSY:
               eNum = errInfo.GetArg();
               if (!eText || !(*eText)) eText = "Provider is busy.";
               DEBUG(path <<" dly " <<eNum <<' ' <<eText);
               if (eNum <= 0) eNum = 1;
               eInfo->setErrInfo(eNum, eText);
               Stats.Bump(Stats.ReqStalls);
               return eNum;
               break;
          default:
               if (!eText || !(*eText)) eText = XrdSysE2T(eNum);
               DEBUG(path <<" err " <<eNum <<' ' <<eText);
               eInfo->setErrInfo(eNum, eText);
               Stats.Bump(Stats.ReqPrepErrs);
               return SFS_ERROR;
               break;
         };
 
// Something is quite wrong here
//
   Log.Emsg(epname, "Provider redirect returned no target host name!");
   eInfo->setErrInfo(ENOMSG, "Server logic error");
   Stats.Bump(Stats.ReqPrepErrs);
   return SFS_ERROR;
}
  
/******************************************************************************/
/*                                  r e a d                                   */
/******************************************************************************/
 
XrdSfsXferSize XrdSsiFileSess::read(XrdSfsFileOffset  offset,    // In
                                    char             *buff,      // Out
                                    XrdSfsXferSize    blen)      // In
/*
  Function: Read `blen' bytes at `offset' into 'buff' and return the actual
            number of bytes read.
 
  Input:    offset    - Contains request information.
            buff      - Address of the buffer in which to place the data.
            blen      - The size of the buffer. This is the maximum number
                        of bytes that will be returned.
 
  Output:   Returns the number of bytes read upon success and SFS_ERROR o/w.
*/
{
   static const char *epname = "read";
   XrdSsiRRInfo   rInfo(offset);
   XrdSsiRRTableItem<XrdSsiFileReq> rqstP;
   XrdSfsXferSize retval;
   unsigned int   reqID = rInfo.Id();
   bool           noMore = false;
 
// Find the request object. If not there we may have encountered an eof
//
   if (!(rqstP = rTab.LookUp(reqID)))
      {if (eofVec.IsSet(reqID))
          {eofVec.UnSet(reqID);
           return 0;
          }
        return XrdSsiUtils::Emsg(epname, ESRCH, "read", gigID, *eInfo);
       }
 
// Simply effect the read via the request object
//
   retval = rqstP->Read(noMore, buff, blen);
 
// See if we just completed this request
//
   if (noMore)
      {rTab.DelFinalize(std::move(rqstP));
       eofVec.Set(reqID);
      }
 
// All done
//
   return retval;
}
  
/******************************************************************************/
/*                               R e c y c l e                                */
/******************************************************************************/
 
void XrdSsiFileSess::Recycle()
{
 
// Do an immediate reset on ourselves to avoid getting too many locks
//
   Reset();
 
// Get a lock
//
   arMutex.Lock();
 
// Check if we should place this on the free list or simply delete it
//
   if (freeNum < freeMax)
      {nextFree = freeList;
       freeList = this;
       freeNum++;
       arMutex.UnLock();
      } else {
       arMutex.UnLock();
       delete this;
      }
}
 
/******************************************************************************/
/* Private:                        R e s e t                                  */
/******************************************************************************/
  
void XrdSsiFileSess::Reset()
{
 
// Close this session
//
   if (isOpen) close(true);
 
// Release other buffers
//
   if (tident) free(tident);
   if (fsUser) free(fsUser);
   if (gigID)  free(gigID);
}
  
/******************************************************************************/
/*                              S e n d D a t a                               */
/******************************************************************************/
  
int XrdSsiFileSess::SendData(XrdSfsDio         *sfDio,
                             XrdSfsFileOffset   offset,
                             XrdSfsXferSize     size)
{
   static const char *epname = "SendData";
   XrdSsiRRInfo   rInfo(offset);
   XrdSsiRRTableItem<XrdSsiFileReq> rqstP;
   unsigned int reqID = rInfo.Id();
   int rc;
 
// Find the request object
//
   if (!(rqstP = rTab.LookUp(reqID)))
      return XrdSsiUtils::Emsg(epname, ESRCH, "send", gigID, *eInfo);
 
// Simply effect the send via the request object
//
   rc = rqstP->Send(sfDio, size);
 
// Determine how this ended
//
   if (rc > 0) rc = SFS_OK;
      else rTab.DelFinalize(std::move(rqstP));
 
   return rc;
}
 
/******************************************************************************/
/*                              t r u n c a t e                               */
/******************************************************************************/
 
int XrdSsiFileSess::truncate(XrdSfsFileOffset  flen)  // In
/*
  Function: Set the length of the file object to 'flen' bytes.
 
  Input:    flen      - The new size of the file.
 
  Output:   Returns SFS_ERROR a this function is not supported.
*/
{
   static const char *epname = "trunc";
   XrdSsiRRTableItem<XrdSsiFileReq> rqstP;
   XrdSsiRRInfo       rInfo(flen);
   XrdSsiRRInfo::Opc  reqXQ = rInfo.Cmd();
   unsigned int       reqID = rInfo.Id();
 
// Find the request object. If not there we may have encountered an eof
//
   if (!(rqstP = rTab.LookUp(reqID)))
      {if (eofVec.IsSet(reqID))
          {eofVec.UnSet(reqID);
           return 0;
          }
        return XrdSsiUtils::Emsg(epname, ESRCH, "cancel", gigID, *eInfo);
       }
 
// Process request (this can only be a cancel request)
//
   if (reqXQ != XrdSsiRRInfo::Can)
      return XrdSsiUtils::Emsg(epname, ENOTSUP, "trunc", gigID, *eInfo);
 
// Perform the cancellation
//
   DEBUG(reqID <<':' <<gigID <<" cancelled");
   rTab.DelFinalize(std::move(rqstP));
   return SFS_OK;
}
 
/******************************************************************************/
/*                                 w r i t e                                  */
/******************************************************************************/
 
XrdSfsXferSize XrdSsiFileSess::write(XrdSfsFileOffset  offset,    // In
                                     const char       *buff,      // In
                                     XrdSfsXferSize    blen)      // In
/*
  Function: Write `blen' bytes at `offset' from 'buff' and return the actual
            number of bytes written.
 
  Input:    offset    - The absolute byte offset at which to start the write.
            buff      - Address of the buffer from which to get the data.
            blen      - The size of the buffer. This is the maximum number
                        of bytes that will be written to 'fd'.
 
  Output:   Returns the number of bytes written upon success and SFS_ERROR o/w.
 
  Notes:    An error return may be delayed until the next write(), close(), or
            sync() call.
*/
{
   static const char *epname = "write";
   XrdSsiRRInfo   rInfo(offset);
   unsigned int reqID = rInfo.Id();
   int reqPass;
 
// Check if we are reading a request segment and handle that. This assumes that
// writes to different requests cannot be interleaved (which they can't be).
//
   if (inProg) return writeAdd(buff, blen, reqID);
 
// Make sure this request does not refer to an active request
//
   if (rTab.LookUp(reqID))
      return XrdSsiUtils::Emsg(epname, EADDRINUSE, "write", gigID, *eInfo);
 
// The offset contains the actual size of the request, make sure it's OK. Note 
// that it can be zero and by convention the blen must be one if so.
//
   reqPass = reqSize = rInfo.Size();
   if (reqSize < blen)
      {if (reqSize || blen != 1)
          return XrdSsiUtils::Emsg(epname, EPROTO, "write", gigID, *eInfo);
       reqSize = 1;
      } else if (reqSize < 0 || reqSize > maxRSZ)
                return XrdSsiUtils::Emsg(epname, EFBIG, "write", gigID, *eInfo);
 
// Indicate we are in the progress of collecting the request arguments
//
   inProg = true;
   eofVec.UnSet(reqID);
 
// Do some debugging
//
   DEBUG(reqID <<':' <<gigID <<" rsz=" <<reqSize <<" wsz=" <<blen);
 
// If the complete request is here then grab the buffer, transfer ownership to
// the request object, and then activate it for processing.
//
   if (reqSize == blen && xioP)
      {XrdSfsXioHandle bRef = xioP->Claim(buff, reqSize, minRSZ);
       if (!bRef)
          {if (errno) Log.Emsg(epname,"Xio.Claim() failed;",XrdSysE2T(errno));}
          else {if (!NewRequest(reqID, 0, bRef, reqPass))
                   return XrdSsiUtils::Emsg(epname,ENOMEM,"write xio",gigID,*eInfo);
                return blen;
               }
      }
 
// The full request is not present, so get a buffer to piece it together
//
   if (!(oucBuff = BuffPool->Alloc(reqSize)))
      return XrdSsiUtils::Emsg(epname, ENOMEM, "write alloc", gigID, *eInfo);
 
// Setup to buffer this
//
   reqLeft = reqSize - blen;
   memcpy(oucBuff->Data(), buff, blen);
   if (!reqLeft)
      {oucBuff->SetLen(reqSize);
 
       if (!NewRequest(reqID, oucBuff, 0, reqPass))
          return XrdSsiUtils::Emsg(epname, ENOMEM, "write sfs", gigID, *eInfo);
       oucBuff = 0;
      } else oucBuff->SetLen(blen, blen);
   return blen;
}
 
/******************************************************************************/
/* Private:                     w r i t e A d d                               */
/******************************************************************************/
 
XrdSfsXferSize XrdSsiFileSess::writeAdd(const char     *buff,      // In
                                        XrdSfsXferSize  blen,      // In
                                        unsigned int    rid)
/*
  Function: Add `blen' bytes from 'buff' to request and return the actual
            number of bytes added.
 
  Input:    buff      - Address of the buffer from which to get the data.
            blen      - The size of the buffer. This is the maximum number
                        of bytes that will be added.
 
  Output:   Returns the number of bytes added upon success and SFS_ERROR o/w.
 
  Notes:    An error return may be delayed until the next write(), close(), or
            sync() call.
*/
{
   static const char *epname = "writeAdd";
   int dlen;
 
// Make sure the caller is not exceeding the size stated on the first write
//
   if (blen > reqLeft)
      return XrdSsiUtils::Emsg(epname, EFBIG, "writeAdd", gigID, *eInfo);
 
// Append the bytes
//
   memcpy(oucBuff->Data(dlen), buff, blen);
 
// Adjust how much we have left
//
   reqLeft -= blen;
   DEBUG(rid <<':' <<gigID <<" rsz=" <<reqLeft <<" wsz=" <<blen);
 
// If we have a complete request. Transfer the buffer ownership to the request
// object and activate processing.
//
   if (!reqLeft)
      {oucBuff->SetLen(reqSize);
       if (!NewRequest(rid, oucBuff, 0, reqSize))
          return XrdSsiUtils::Emsg(epname, ENOMEM, "write", gigID, *eInfo);
       oucBuff = 0;
      } else {
       dlen += blen;
       oucBuff->SetLen(dlen, dlen);
      }
 
// Return how much we appended
//
   return blen;
}