1// SPDX-License-Identifier: GPL-2.0-or-later
  2/* Direct I/O support.
  3 *
  4 * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
  5 * Written by David Howells (dhowells@redhat.com)
  6 */
  7
  8#include <linux/export.h>
  9#include <linux/fs.h>
 10#include <linux/mm.h>
 11#include <linux/pagemap.h>
 12#include <linux/slab.h>
 13#include <linux/uio.h>
 14#include <linux/sched/mm.h>
 15#include <linux/task_io_accounting_ops.h>
 16#include <linux/netfs.h>
 17#include "internal.h"
 18
 19/**
 20 * netfs_unbuffered_read_iter_locked - Perform an unbuffered or direct I/O read
 21 * @iocb: The I/O control descriptor describing the read
 22 * @iter: The output buffer (also specifies read length)
 23 *
 24 * Perform an unbuffered I/O or direct I/O from the file in @iocb to the
 25 * output buffer.  No use is made of the pagecache.
 26 *
 27 * The caller must hold any appropriate locks.
 28 */
 29static ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_iter *iter)
 30{
 31	struct netfs_io_request *rreq;
 32	ssize_t ret;
 33	size_t orig_count = iov_iter_count(iter);
 34	bool async = !is_sync_kiocb(iocb);
 35
 36	_enter("");
 37
 38	if (!orig_count)
 39		return 0; /* Don't update atime */
 40
 41	ret = kiocb_write_and_wait(iocb, orig_count);
 42	if (ret < 0)
 43		return ret;
 44	file_accessed(iocb->ki_filp);
 45
 46	rreq = netfs_alloc_request(iocb->ki_filp->f_mapping, iocb->ki_filp,
 47				   iocb->ki_pos, orig_count,
 48				   NETFS_DIO_READ);
 49	if (IS_ERR(rreq))
 50		return PTR_ERR(rreq);
 51
 52	netfs_stat(&netfs_n_rh_dio_read);
 53	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_dio_read);
 54
 55	/* If this is an async op, we have to keep track of the destination
 56	 * buffer for ourselves as the caller's iterator will be trashed when
 57	 * we return.
 58	 *
 59	 * In such a case, extract an iterator to represent as much of the the
 60	 * output buffer as we can manage.  Note that the extraction might not
 61	 * be able to allocate a sufficiently large bvec array and may shorten
 62	 * the request.
 63	 */
 64	if (user_backed_iter(iter)) {
 65		ret = netfs_extract_user_iter(iter, rreq->len, &rreq->iter, 0);
 66		if (ret < 0)
 67			goto out;
 68		rreq->direct_bv = (struct bio_vec *)rreq->iter.bvec;
 69		rreq->direct_bv_count = ret;
 70		rreq->direct_bv_unpin = iov_iter_extract_will_pin(iter);
 71		rreq->len = iov_iter_count(&rreq->iter);
 72	} else {
 73		rreq->iter = *iter;
 74		rreq->len = orig_count;
 75		rreq->direct_bv_unpin = false;
 76		iov_iter_advance(iter, orig_count);
 77	}
 78
 79	// TODO: Set up bounce buffer if needed
 80
 81	if (async)
 82		rreq->iocb = iocb;
 83
 84	ret = netfs_begin_read(rreq, is_sync_kiocb(iocb));
 85	if (ret < 0)
 86		goto out; /* May be -EIOCBQUEUED */
 87	if (!async) {
 88		// TODO: Copy from bounce buffer
 89		iocb->ki_pos += rreq->transferred;
 90		ret = rreq->transferred;
 91	}
 92
 93out:
 94	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
 95	if (ret > 0)
 96		orig_count -= ret;
 97	if (ret != -EIOCBQUEUED)
 98		iov_iter_revert(iter, orig_count - iov_iter_count(iter));
 99	return ret;
100}
101
102/**
103 * netfs_unbuffered_read_iter - Perform an unbuffered or direct I/O read
104 * @iocb: The I/O control descriptor describing the read
105 * @iter: The output buffer (also specifies read length)
106 *
107 * Perform an unbuffered I/O or direct I/O from the file in @iocb to the
108 * output buffer.  No use is made of the pagecache.
109 */
110ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter)
111{
112	struct inode *inode = file_inode(iocb->ki_filp);
113	ssize_t ret;
114
115	if (!iter->count)
116		return 0; /* Don't update atime */
117
118	ret = netfs_start_io_direct(inode);
119	if (ret == 0) {
120		ret = netfs_unbuffered_read_iter_locked(iocb, iter);
121		netfs_end_io_direct(inode);
122	}
123	return ret;
124}
125EXPORT_SYMBOL(netfs_unbuffered_read_iter);