Robert Newson created COUCHDB-3274:
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Summary: eof in couch_file can be incorrect after error
Key: COUCHDB-3274
URL: https://issues.apache.org/jira/browse/COUCHDB-3274
Project: CouchDB
Issue Type: Bug
Reporter: Robert Newson
It's possible for a file:write call to write some of the requested data but
then return an error ({error, enospc}, for example).
In 2010 we started tracking eof in couch_file state, where previously we called
file:position(Fd, eof) and used that value, which was always correct. In
success cases we advance the eof value by the correct amount but in error cases
we don't advance it at all.
A simple fix is to call file:position(Fd, eof) in the error cases and set the
eof field to that value.
The upshot of this bug is that data written to the file once eof is wrong is
essentially corrupt in that we'll look for it at the wrong offsets. Given this
would typically when a filesystem runs completely out of space, in most cases
it would not cause issues (we wouldn't be able to write a header that pointed
to this) but if space were then recovered (and the couch_file had not closed or
crashed) then corruption seems assured.
I have a patch for this and I certainly welcome opinions on severity (and,
indeed, if I'm flat wrong).
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