Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > (1) If the page is not up to date, then we should just return 0 > > (ie. indicating a zero-length copy). The loop in > > generic_perform_write() will go around again, possibly breaking up the > > iterator into discrete chunks. > > Does this actually work? What about the situation where you're reading > the last page of a file and thus (almost) always reading fewer bytes > than a PAGE_SIZE? Al Viro made such a change for Ceph - and we're writing, not reading. I was thinking that it would break if reading from a pipe, but Jeff pointed out that the iov_iter_advance() in generic_perform_write() uses the return value of ->write_end() to advance the iterator. So it might loop endlessly, but it doesn't appear it will corrupt your data. David
