On Wed, Dec 05, 2018 at 09:31:02AM +1100, Dave Chinner wrote: > That's what the code does right now and *exactly what I'm trying to > fix* because it EINVAL is ambiguous and not an indicator that we've > reached the end of the source file. EINVAL can indicate several > different errors, so it really has to be treated as a "copy failed" > error by applications. > > Have a look at read/pread() - they return 0 in this case to indicate > a short read, and the value of zero is explicitly defined as meaning > "read position is beyond EOF". Applications know straight away that > there is no more data to be read and there was no error, so can > terminate on a successful short read. > > We need to allow applications to terminate copy loops on a > successful short copy. I'm a little confused by your definition of "short copy" and "short read". Are you using that to mean a copy/read that returns zero? I usually see it used to mean any successful call that returned less than the requested amount. I'd expect a zero return to terminate a copy loop, but not any positive return. --b. > IOWs, applications need to either: > > - get an immediate error saying the range is invalid rather > than doing a short copy (as per the man page); or > - have an explicit marker to say "no more data to be copied" > > Applications need the "no more data to copy" case to be explicit and > unambiguous so they can make sane decisions about whether a short > copy was successful because the file was shorter than expected or > whether a short copy was a result of a real error being encountered. > The current behaviour is largely unusable for applications because > they have to guess at the reason for EINVAL part way through a > copy.... > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx
