Cephsum is intended as a simple alternative for performing checksum operations in xrootd on Ceph object-store systems using librados. The basic command will get / caclulate the checksum via whatever means, and write the checksum into the ceph xattr if needed, following the XrootD XrdCks binary file format. Little-endian format is used; following the gridFTP implementation (which is likely different to the default xrdadler32 and XrdCks method.)
The package was designed to rely on a minimal set of external dependencies. This is python3 only (and tested only against 3.6.8 sofar) and needs the librados python bindings.
Main motivation for this package is to replace the internal XrootD checksum implemetation with a simple external script. As such a few modifications to the xrootd.cfg are required.
In addition, xrootd external checksum scripts only provide the LFN on the path, not the converted PFN. Using -x storage.xml,
this functionality can be recovered.
An example script is included in the scripts/ directory for use with xrootd
Within the xrootd configuration file, the following settings are suggested (feedback on better is welcome!)
# ensure cksum adler32 is included in the tpc directive, in order to caclulate by default on transfer
ofs.tpc cksum adler32 fcreds ?gsi =X509_USER_PROXY autorm xfr 40 pgm /etc/xrootd/xrdcp-tpc.sh
# add this line to trigger external checksum calculation. Would be overwritten by other xrootd.chksum lines
xrootd.chksum max 50 adler32 /etc/xrootd/xrd_cephsum.sh
python3 cephsum.py --action=inget -x storage.xml dteam:test1/testfile.root
The above command should get / caclulate the checksum via whatever means, and write the checksum into the ceph xattr if needed, following the XrootD XrdCks binary file format. Little-endiany
The original gridFTP plugin uses little-endian formatting to write the binary data into the xattr. This appears to be only relevant for the timestamp (fmtime) and timedelta (cstime) values. In the usual configuration, if a big-endian formatted xattr is found, it is converted to little-endian and overwrites the original metadata object
Only a basic set of unit tests is currently provided; can be run for example via:
python3 -m unittest discover tests
An example script is included in the scripts/ directory for use with xrootd
Default example; read a checksum from metadata if possible, else calculate from file and insert back into metadata:
python3 cephsum.py --action=inget dteam:test1/testfile.root
Read cehcksum, from metadata, or file if ncessary. Don't write back any caclulated checksum
python3 cephsum.py --action=get dteam:test1/testfile.root
Use a storage.xml file, used in xrootd for lfn2pfn mapping
python3 cephsum.py --action=inget -x storage.xml dteam:test1/testfile.root
Get checksum from only metadata, or file. Don't store any checksum back however
python3 cephsum.py --action=metaonly dteam:test1/testfile.root
python3 cephsum.py --action=fileonly dteam:test1/testfile.root
Compare stored checksum to file-calculated checksum, If -C adler32: is provided, then also compare to the provided checksum
python3 cephsum.py --action=verify dteam:test1/testfile.root
python3 cephsum.py --action=verify -C adler32:95413e91 dteam:test1/testfile.root
Check given checksum against source checksum provided by -C adler32:. if not in metadata, calculate and insert to metadata if matches
python3 cephsum.py --action=check -C adler32:95413e91 dteam:test1/testfile.root