Commit d0497dd2 authored by Mike Snitzer's avatar Mike Snitzer Committed by Anna Schumaker
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nfs/localio: backfill missing partial read support for misaligned DIO 



Misaligned DIO read can be split into 3 IOs, must handle potential for
short read from each component IO (follows same pattern used for
handling partial writes, except upper layer read code handles advancing
offset before retry).

Fixes: c817248f ("nfs/localio: add proper O_DIRECT support for READ and WRITE")
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
Signed-off-by: default avatarAnna Schumaker <anna.schumaker@oracle.com>
parent f2060bdc

fs/nfs/localio.c

+20 −4
Original line number Diff line number Diff line
@@ -414,7 +414,7 @@ nfs_local_iters_setup_dio(struct nfs_local_kiocb *iocb, int rw, 
	/* Setup misaligned end?

	 * If so, the end is purposely setup to be issued using buffered IO

	 * before the middle (which will use DIO, if DIO-aligned, with AIO).

	 * This creates problems if/when the end results in a partial write.

	 * This creates problems if/when the end results in short read or write.

	 * So must save index and length of end to handle this corner case.

	 */

	if (local_dio->end_len) {
@@ -580,8 +580,9 @@ static void nfs_local_read_done(struct nfs_local_kiocb *iocb) 
	 */

	hdr->res.replen = 0;



	if (hdr->res.count != hdr->args.count ||

	    hdr->args.offset + hdr->res.count >= i_size_read(file_inode(filp)))

	/* nfs_readpage_result() handles short read */



	if (hdr->args.offset + hdr->res.count >= i_size_read(file_inode(filp)))

		hdr->res.eof = true;



	dprintk("%s: read %ld bytes eof %d.\n", __func__,
@@ -620,6 +621,7 @@ static void nfs_local_call_read(struct work_struct *work) 
		container_of(work, struct nfs_local_kiocb, work);

	struct file *filp = iocb->kiocb.ki_filp;

	const struct cred *save_cred;

	bool force_done = false;

	ssize_t status;

	int n_iters;
@@ -637,7 +639,21 @@ static void nfs_local_call_read(struct work_struct *work) 
		iocb->kiocb.ki_pos = iocb->offset[i];

		status = filp->f_op->read_iter(&iocb->kiocb, &iocb->iters[i]);

		if (status != -EIOCBQUEUED) {

			if (nfs_local_pgio_done(iocb, status, false)) {

			if (unlikely(status >= 0 && status < iocb->iters[i].count)) {

				/* partial read */

				if (i == iocb->end_iter_index) {

					/* Must not account DIO partial end, otherwise (due

					 * to end being issued before middle): the partial

					 * read accounting in nfs_local_read_done()

					 * would incorrectly advance hdr->args.offset

					 */

					status = 0;

				} else {

					/* Partial read at start or middle, force done */

					force_done = true;

				}

			}

			if (nfs_local_pgio_done(iocb, status, force_done)) {

				nfs_local_read_iocb_done(iocb);

				break;

			}