Example of proposed XrdOss advanced error interface usage

src/XrdOfs/XrdOfs.cc

@@ -737,7 +737,7 @@ int XrdOfsFile::open(const char          *path,      // In
           }
        if (XrdOfsFS->Balancer && retc == -ENOENT)
           XrdOfsFS->Balancer->Removed(path);
-       return XrdOfsFS->Emsg(epname, error, retc, "open", path);
+       return XrdOfsFS->Emsg(epname, error, retc, "open", path, oP.fP);
       }
 
 // Verify that we can actually use this file
@@ -2555,6 +2555,44 @@ int XrdOfs::Emsg(const char    *pfx,    // Message prefix value
     return SFS_ERROR;
 }
 
+/******************************************************************************/
+
+int XrdOfs::Emsg(const char    *pfx,    // Message prefix value
+                 XrdOucErrInfo &einfo,  // Place to put text & error code
+                 int            ecode,  // The error code
+                 const char    *op,     // Operation being performed
+                 const char    *target, // The target (e.g., fname)
+                 const XrdOssDF *fP)    // The file object generating this error
+{
+   char buffer[MAXPATHLEN+80];
+
+// If the error is EBUSY then we just need to stall the client. This is
+// a hack in order to provide for proxy support
+//
+    if (ecode < 0) ecode = -ecode;
+    if (ecode == EBUSY) return 5;  // A hack for proxy support
+
+// Check for timeout conditions that require a client delay
+//
+   if (ecode == ETIMEDOUT) return OSSDelay;
+
+// Format the error message
+//
+   XrdOucERoute::Format(buffer, sizeof(buffer), ecode, op, target);
+
+// Print it out if debugging is enabled
+//
+#ifndef NODEBUG
+    OfsEroute.Emsg(pfx, einfo.getErrUser(), buffer);
+#endif
+
+// Place the error message in the error object and return
+//
+    const XrdOucErrInfo *chainedErr = (OssHasErr && fP) ? fP->getError() : nullptr;
+    einfo.setErrInfo(ecode, buffer, chainedErr);
+    return SFS_ERROR;
+}
+
 /******************************************************************************/
 /*                     P R I V A T E    S E C T I O N                         */
 /******************************************************************************/

src/XrdOfs/XrdOfs.hh

@@ -433,6 +433,8 @@ static  int   Emsg(const char *, XrdOucErrInfo  &, int, const char *x,
                    XrdOfsHandle *hP);
 static  int   Emsg(const char *, XrdOucErrInfo  &, int, const char *x,
                    const char *y="");
+        int   Emsg(const char *, XrdOucErrInfo  &, int, const char *opName,
+                   const char *path, const XrdOssDF *fP);
 static  int   fsError(XrdOucErrInfo &myError, int rc);
 const char   *Split(const char *Args, const char **Opq, char *Path, int Plen);
         int   Stall(XrdOucErrInfo  &, int, const char *);
@@ -480,6 +482,7 @@ XrdSysMutex              ocMutex; // Global mutex for open/close
 bool              DirRdr;         // Opendir() can be redirected.
 bool              reProxy;        // Reproxying required for TPC
 bool              OssHasPGrw;     // True: oss implements full rgRead/Write
+bool              OssHasErr;      // True if the OSS can produce error messages
 
 /******************************************************************************/
 /*                            O t h e r   D a t a                             */

src/XrdOfs/XrdOfsConfig.cc

@@ -357,6 +357,10 @@ int XrdOfs::Configure(XrdSysError &Eroute, XrdOucEnv *EnvInfo) {
 //
    OssHasPGrw = (ossFeatures & XRDOSS_HASPGRW) != 0;
 
+// Indicate whether the oss implementation has getError for additional error
+// message information.
+   OssHasErr = (ossFeatures & XRDOSS_HASAERR);
+
 // If POSC processing is enabled (as by default) do it. Warning! This must be
 // the last item in the configuration list as we need a working filesystem.
 // Note that in proxy mode we always disable posc!

src/XrdOss/XrdOss.cc

@@ -69,6 +69,14 @@ int XrdOss::FSctl(int cmd, int alen, const char *args, char **resp)
    return -ENOTSUP;
 }
 
+/******************************************************************************/
+/*                            g e t E r r o r                                 */
+/******************************************************************************/
+const XrdOucErrInfo *XrdOss::getError() const
+{
+   return nullptr;
+}
+
 /******************************************************************************/
 /*                                 R e l o c                                  */
 /******************************************************************************/
@@ -153,6 +161,14 @@ int XrdOssDF::Fctl(int cmd, int alen, const char *args, char **resp)
    return -ENOTSUP;
 }
 
+/******************************************************************************/
+/*                            g e t E r r o r                                 */
+/******************************************************************************/
+const XrdOucErrInfo *XrdOssDF::getError() const
+{
+   return nullptr;
+}
+
 /******************************************************************************/
 /*                                p g R e a d                                 */
 /******************************************************************************/

src/XrdOss/XrdOss.hh

@@ -39,10 +39,12 @@
 #include <sys/types.h>
 #include <cstring>
 
+#include "XrdVersion.hh"
 #include "XrdOss/XrdOssVS.hh"
 #include "XrdOuc/XrdOucIOVec.hh"
 
 class XrdOucEnv;
+class XrdOucErrInfo;
 class XrdSysLogger;
 class XrdSfsAio;
 
@@ -447,6 +449,21 @@ const char     *getTID() {return tident;}
 
 virtual        ~XrdOssDF() {}
 
+//-----------------------------------------------------------------------------
+//! Return advanced error information about the last error encountered by
+//! this object.  Only invoked if the XrdOSS indicates it has feature XRDOSS_AERR
+//! The advanced error feature provides the ability for more error information
+//! than is possible from the typical error code (e.g., unstructured error
+//! messages).
+//!
+//! @return Error object associated with the last error.  Caller does not own
+//! the returned memory.  Lifetime of the returned object is only guaranteed
+//! until the next method call.  May return nullptr even if an error occurred.
+//-----------------------------------------------------------------------------
+
+#if XrdMajorVNUM(XrdVNUMBER) > 5 || defined(__GNUC__)
+virtual const XrdOucErrInfo *getError() const;
+#endif
 
 protected:
 
@@ -479,6 +496,7 @@ short       rsvd;    // Reserved
 #define XRDOSS_HASCACH 0x0000000000000010ULL
 #define XRDOSS_HASNAIO 0x0000000000000020ULL
 #define XRDOSS_HASRPXY 0x0000000000000040ULL
+#define XRDOSS_HASAERR 0x0000000000000080ULL
 
 // Options that can be passed to Stat()
 //
@@ -895,6 +913,23 @@ const char       *Lfn2Pfn(const char *Path, char *buff, int blen, int &rc)
 
                 XrdOss() {}
 virtual        ~XrdOss() {}
+
+//-----------------------------------------------------------------------------
+//! Return advanced error information about the last error encountered by
+//! this object.  Only invoked if the XrdOSS indicates it has feature XRDOSS_AERR
+//! The advanced error feature provides the ability for more error information
+//! than is possible from the typical error code (e.g., unstructured error
+//! messages).
+//!
+//! @return Error object associated with the last error.  Caller does not own
+//! the returned memory.  Lifetime of the returned object is only guaranteed
+//! until the next method call.  May return nullptr even if an error occurred.
+//-----------------------------------------------------------------------------
+
+#if XrdMajorVNUM(XrdVNUMBER) > 5 || defined(__GNUC__)
+virtual const XrdOucErrInfo *getError() const;
+#endif
+
 };
 
 /******************************************************************************/

src/XrdOuc/XrdOucErrInfo.hh

@@ -138,14 +138,23 @@ inline int   setErrCode(int code) {return ErrInfo.code = code;}
 //-----------------------------------------------------------------------------
 //! Set error code and error text.
 //!
-//! @param  code    - The error number describing the error.
-//! @param  emsg    - The error message text.
+//! @param  code           - The error number describing the error.
+//! @param  emsg           - The error message text.
+//! @param  chainedErrInfo - Optionally, an error object triggering the current error
 //!
 //! @return code    - The error number.
 //-----------------------------------------------------------------------------
 
-inline int   setErrInfo(int code, const char *emsg)
-                {strlcpy(ErrInfo.message, emsg, sizeof(ErrInfo.message));
+inline int   setErrInfo(int code, const char *emsg, const XrdOucErrInfo *chainedErrInfo=nullptr)
+                {if (chainedErrInfo && chainedErrInfo->getErrText())
+                    {const char *txtlist[4];
+                     txtlist[0] = emsg;
+                     txtlist[1] = " (";
+                     txtlist[2] = chainedErrInfo->getErrText();
+                     txtlist[3] = ")";
+                     return setErrInfo(code, txtlist, 4);
+                    }
+                 strlcpy(ErrInfo.message, emsg, sizeof(ErrInfo.message));
                  if (dataBuff) {dataBuff->Recycle(); dataBuff = 0;}
                  return ErrInfo.code = code;
                 }
@@ -259,7 +268,7 @@ inline int          getErrInfo(XrdOucEI &errParm)
 //! @return The pointer to the internal error text.
 //-----------------------------------------------------------------------------
 
-inline const char  *getErrText()
+inline const char  *getErrText() const
                        {if (dataBuff) return dataBuff->Data();
                         return (const char *)ErrInfo.message;
                        }

src/XrdPss/XrdPss.cc

@@ -157,7 +157,7 @@ XrdOss *XrdOssGetStorageSystem2(XrdOss       *native_oss,
 
 XrdPssSys::XrdPssSys() : LocalRoot(0), theN2N(0), DirFlags(0),
                          myVersion(&XrdVERSIONINFOVAR(XrdOssGetStorageSystem2)),
-                         myFeatures(XRDOSS_HASPRXY|XRDOSS_HASPGRW|XRDOSS_HASNOSF)
+                         myFeatures(XRDOSS_HASPRXY|XRDOSS_HASPGRW|XRDOSS_HASNOSF|XRDOSS_HASAERR)
                          {}
 
 /******************************************************************************/
@@ -816,7 +816,13 @@ int XrdPssFile::Open(const char *path, int Oflag, mode_t Mode, XrdOucEnv &Env)
 // Try to open and if we failed, return an error
 //
    if (!XrdPssSys::dcaCheck || !ioCache)
-      {if ((fd = XrdPosixXrootd::Open(pbuff,Oflag,Mode)) < 0) return -errno;
+      {if ((fd = XrdPosixXrootd::Open(pbuff,Oflag,Mode)) < 0)
+          {const char *txtlist[2];
+           txtlist[0] = "Failed to open file in cache: ";
+           txtlist[1] = XrdSysError::ec2text(errno);
+           errInfo.setErrInfo(errno, txtlist, 2);
+           return -errno;
+          }
       } else {
        XrdPosixInfo Info;
        Info.ffReady = XrdPssSys::dcaWorld;

src/XrdPss/XrdPss.hh

@@ -35,6 +35,7 @@
 #include <sys/types.h>
 #include <vector>
 #include "XrdSys/XrdSysHeaders.hh"
+#include "XrdOuc/XrdOucErrInfo.hh"
 #include "XrdOuc/XrdOucExport.hh"
 #include "XrdOuc/XrdOucName2Name.hh"
 #include "XrdOuc/XrdOucPList.hh"
@@ -85,6 +86,7 @@ int     Fstat(struct stat *);
 int     Fsync();
 int     Fsync(XrdSfsAio *aiop);
 int     Ftruncate(unsigned long long);
+const XrdOucErrInfo *getError() const override {return &errInfo;}
 ssize_t pgRead (void* buffer, off_t offset, size_t rdlen,
                 uint32_t* csvec, uint64_t opts);
 int     pgRead (XrdSfsAio* aioparm, uint64_t opts);
@@ -125,6 +127,8 @@ struct tprInfo
 
       char         *tpcPath;
 const XrdSecEntity *entity;
+
+XrdOucErrInfo errInfo; // Error info object for advanced error reporting.
 };
 
 /******************************************************************************/
@@ -159,6 +163,7 @@ virtual
 int       Create(const char *, const char *, mode_t, XrdOucEnv &, int opts=0);
 void      EnvInfo(XrdOucEnv *envP);
 uint64_t  Features() {return myFeatures;}
+const XrdOucErrInfo *getError() const override {return &errInfo;}
 int       Init(XrdSysLogger *, const char *) override {return -ENOTSUP;}
 int       Init(XrdSysLogger *, const char *, XrdOucEnv *envP) override;
 int       Lfn2Pfn(const char *Path, char *buff, int blen);
@@ -216,6 +221,7 @@ unsigned long long DirFlags; // Defaults for exports
 XrdVersionInfo    *myVersion;// -> Compilation version
 XrdSecsssID       *idMapper; // -> Auth ID mapper
 uint64_t          myFeatures;// Our feature set
+XrdOucErrInfo     errInfo;   // Err info object for improved error message reporting
 
 int    Configure(const char *, XrdOucEnv *);
 int    ConfigProc(const char *ConfigFN);