iomap: partially revert 4721a601 (simulated directio short read on EFAULT)
In commit 4721a601, we tried to fix a problem wherein directio reads into a splice pipe will bounce EFAULT/EAGAIN all the way out to userspace by simulating a zero-byte short read. This happens because some directio read implementations (xfs) will call bio_iov_iter_get_pages to grab pipe buffer pages and issue asynchronous reads, but as soon as we run out of pipe buffers that _get_pages call returns EFAULT, which the splice code translates to EAGAIN and bounces out to userspace. In that commit, the iomap code catches the EFAULT and simulates a zero-byte read, but that causes assertion errors on regular splice reads because xfs doesn't allow short directio reads. This causes infinite splice() loops and assertion failures on generic/095 on overlayfs because xfs only permit total success or total failure of a directio operation. The underlying issue in the pipe splice code has now been fixed by changing the pipe splice loop to avoid avoid reading more data than there is space in the pipe. Therefore, it's no longer necessary to simulate the short directio, so remove the hack from iomap. Fixes: 4721a601 ("iomap: dio data corruption and spurious errors when pipes fill") Reported-by:Murphy Zhou <jencce.kernel@gmail.com> Ranted-by: