Hi folks:
I've been using sparse files on xfs for a while, and every now and
then have the pleasure of copying them. Using coreutils cp (standard
linux cp) usually winds up with the utility seeking through the entire
file (yes, even with with the --sparse=* options set).
It seems to me that the code is blissfully unware of the file
extents, and its sparse implementation amounts to a read, a check to see
if it needs to write it as a hole, write it, and the next seek. Iterate
until done.
Here's my question. Is there a way to (easily) programmatically hand
cp (or any other utility) something akin to the output of xfs_bmap, and
thus save it potentially *gargantuan* amounts of seeking over known zero
regions? File sparsity in these cases are from 80-99% in some cases
(fills of 1-20%) for multi GB/TB sized files.
Pointers appreciated. I am looking at the copy routines in coreutils
now, looking to see if we can increase its intelligence somewhat w.r.t.
sparse files.
Thanks!
Joe
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