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If you try to read the entire file until the end of file with the file cache then it can either fail with an error, or silently return more data than is in the source file:
[illingwo@fermicloud058 ~]$ export XROOTD_VMP=mwt2-stashcache.campuscluster.illinois.edu:/stash=
[illingwo@fermicloud058 ~]$ export LD_PRELOAD=/usr/lib64/libXrdPosixPreload.so
[illingwo@fermicloud058 ~]$ ls -l /stash/pnfs/fnal.gov/usr/nova/data/flux/gsimple/nova_v06/nd/mn/rhc/gsimple_NOvA-ND_mn000z-200i_rp11_bs1.1_pnut_lowth_f11f093bbird_target_q72_00001.root
-r-------- 1 illingwo e740 346178381 Apr 9 19:16 /stash/pnfs/fnal.gov/usr/nova/data/flux/gsimple/nova_v06/nd/mn/rhc/gsimple_NOvA-ND_mn000z-200i_rp11_bs1.1_pnut_lowth_f11f093bbird_target_q72_00001.root
[illingwo@fermicloud058 ~]$ XRD_LOGLEVEL=Error cat /stash/pnfs/fnal.gov/usr/nova/data/flux/gsimple/nova_v06/nd/mn/rhc/gsimple_NOvA-ND_mn000z-200i_rp11_bs1.1_pnut_lowth_f11f093bbird_target_q72_00001.root | wc -c
346195610
or
$ XRD_LOGLEVEL=Error wc /stash/pnfs/fnal.gov/usr/nova/data/flux/gsimple/nova_v06/nd/mn/rhc/gsimple_NOvA-ND_mn000z-200i_rp11_bs1.1_pnut_lowth_f11f093bbird_target_q52_00001.root
[2015-07-06 14:47:30.029650 -0500][Error ][XRootD ] [mwt2-stashcache.campuscluster.illinois.edu:1094] Overflow data while reading response to kXR_read (handle: 0x00000000, offset: 346235956, size: 16384): expected: 16384, got 17146 bytes
[2015-07-06 14:47:30.029839 -0500][Error ][XRootD ] [mwt2-stashcache.campuscluster.illinois.edu:1094] Handling response to kXR_read (handle: 0x00000000, offset: 346235956, size: 16384): user supplied buffer is too small for the received data.
[2015-07-06 14:47:30.029875 -0500][Error ][File ] [0x1b68af0@root://mwt2-stashcache.campuscluster.illinois.edu:1094//pnfs/fnal.gov/usr/nova/data/flux/gsimple/nova_v06/nd/mn/rhc/gsimple_NOvA-ND_mn000z-200i_rp11_bs1.1_pnut_lowth_f11f093bbird_target_q52_00001.root] Fatal file state error. Message kXR_read (handle: 0x00000000, offset: 346235956, size: 16384) returned with [ERROR] Invalid response
wc: /stash/pnfs/fnal.gov/usr/nova/data/flux/gsimple/nova_v06/nd/mn/rhc/gsimple_NOvA-ND_mn000z-200i_rp11_bs1.1_pnut_lowth_f11f093bbird_target_q52_00001.root: Bad message
1211905 7186282 346235956 /stash/pnfs/fnal.gov/usr/nova/data/flux/gsimple/nova_v06/nd/mn/rhc/gsimple_NOvA-ND_mn000z-200i_rp11_bs1.1_pnut_lowth_f11f093bbird_target_q52_00001.root
In XrdFileCache/XrdFileCacheIOEntireFile.cc IOEntireFile::Read(), if the call to m_prefetch->Read(buff, off, size); returns less data than size because it's at the end of the file, then the number of bytes actually read is added to bytes_read twice, the first time at line 97, then the second time at line 106.
The corresponding function in XrdFileCache/XrdFileCacheIOFileBlock.cc also appears to be incorrect in this situation, although in a different way: if the actual bytes read doesn't equal the requested read size it returns the size of the final read, regardless of any data it may have previously put into the buffer from previous calls to read.
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