direct_read.c

  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
 19static void netfs_prepare_dio_read_iterator(struct netfs_io_subrequest *subreq)
 20{
 21	struct netfs_io_request *rreq = subreq->rreq;
 22	size_t rsize;
 23
 24	rsize = umin(subreq->len, rreq->io_streams[0].sreq_max_len);
 25	subreq->len = rsize;
 26
 27	if (unlikely(rreq->io_streams[0].sreq_max_segs)) {
 28		size_t limit = netfs_limit_iter(&rreq->buffer.iter, 0, rsize,
 29						rreq->io_streams[0].sreq_max_segs);
 30
 31		if (limit < rsize) {
 32			subreq->len = limit;
 33			trace_netfs_sreq(subreq, netfs_sreq_trace_limited);
 34		}
 35	}
 36
 37	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
 38
 39	subreq->io_iter	= rreq->buffer.iter;
 40	iov_iter_truncate(&subreq->io_iter, subreq->len);
 41	iov_iter_advance(&rreq->buffer.iter, subreq->len);
 42}
 43
 44/*
 45 * Perform a read to a buffer from the server, slicing up the region to be read
 46 * according to the network rsize.
 47 */
 48static int netfs_dispatch_unbuffered_reads(struct netfs_io_request *rreq)
 49{
 50	struct netfs_io_stream *stream = &rreq->io_streams[0];
 51	unsigned long long start = rreq->start;
 52	ssize_t size = rreq->len;
 53	int ret = 0;
 54
 55	do {
 56		struct netfs_io_subrequest *subreq;
 57		ssize_t slice;
 58
 59		subreq = netfs_alloc_subrequest(rreq);
 60		if (!subreq) {
 61			ret = -ENOMEM;
 62			break;
 63		}
 64
 65		subreq->source	= NETFS_DOWNLOAD_FROM_SERVER;
 66		subreq->start	= start;
 67		subreq->len	= size;
 68
 69		__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
 70
 71		spin_lock(&rreq->lock);
 72		list_add_tail(&subreq->rreq_link, &stream->subrequests);
 73		if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
 74			if (!stream->active) {
 75				stream->collected_to = subreq->start;
 76				/* Store list pointers before active flag */
 77				smp_store_release(&stream->active, true);
 78			}
 79		}
 80		trace_netfs_sreq(subreq, netfs_sreq_trace_added);
 81		spin_unlock(&rreq->lock);
 82
 83		netfs_stat(&netfs_n_rh_download);
 84		if (rreq->netfs_ops->prepare_read) {
 85			ret = rreq->netfs_ops->prepare_read(subreq);
 86			if (ret < 0) {
 87				netfs_put_subrequest(subreq, netfs_sreq_trace_put_cancel);
 88				break;
 89			}
 90		}
 91
 92		netfs_prepare_dio_read_iterator(subreq);
 93		slice = subreq->len;
 94		size -= slice;
 95		start += slice;
 96		rreq->submitted += slice;
 97		if (size <= 0) {
 98			smp_wmb(); /* Write lists before ALL_QUEUED. */
 99			set_bit(NETFS_RREQ_ALL_QUEUED, &rreq->flags);
100		}
101
102		rreq->netfs_ops->issue_read(subreq);
103
104		if (test_bit(NETFS_RREQ_PAUSE, &rreq->flags))
105			netfs_wait_for_paused_read(rreq);
106		if (test_bit(NETFS_RREQ_FAILED, &rreq->flags))
107			break;
108		cond_resched();
109	} while (size > 0);
110
111	if (unlikely(size > 0)) {
112		smp_wmb(); /* Write lists before ALL_QUEUED. */
113		set_bit(NETFS_RREQ_ALL_QUEUED, &rreq->flags);
114		netfs_wake_collector(rreq);
115	}
116
117	return ret;
118}
119
120/*
121 * Perform a read to an application buffer, bypassing the pagecache and the
122 * local disk cache.
123 */
124static ssize_t netfs_unbuffered_read(struct netfs_io_request *rreq, bool sync)
125{
126	ssize_t ret;
127
128	_enter("R=%x %llx-%llx",
129	       rreq->debug_id, rreq->start, rreq->start + rreq->len - 1);
130
131	if (rreq->len == 0) {
132		pr_err("Zero-sized read [R=%x]\n", rreq->debug_id);
133		netfs_put_request(rreq, netfs_rreq_trace_put_discard);
134		return -EIO;
135	}
136
137	// TODO: Use bounce buffer if requested
138
139	inode_dio_begin(rreq->inode);
140
141	ret = netfs_dispatch_unbuffered_reads(rreq);
142
143	if (!rreq->submitted) {
144		netfs_put_request(rreq, netfs_rreq_trace_put_no_submit);
145		inode_dio_end(rreq->inode);
146		ret = 0;
147		goto out;
148	}
149
150	if (sync)
151		ret = netfs_wait_for_read(rreq);
152	else
153		ret = -EIOCBQUEUED;
154out:
155	_leave(" = %zd", ret);
156	return ret;
157}
158
159/**
160 * netfs_unbuffered_read_iter_locked - Perform an unbuffered or direct I/O read
161 * @iocb: The I/O control descriptor describing the read
162 * @iter: The output buffer (also specifies read length)
163 *
164 * Perform an unbuffered I/O or direct I/O from the file in @iocb to the
165 * output buffer.  No use is made of the pagecache.
166 *
167 * The caller must hold any appropriate locks.
168 */
169ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_iter *iter)
170{
171	struct netfs_io_request *rreq;
172	ssize_t ret;
173	size_t orig_count = iov_iter_count(iter);
174	bool sync = is_sync_kiocb(iocb);
175
176	_enter("");
177
178	if (!orig_count)
179		return 0; /* Don't update atime */
180
181	ret = kiocb_write_and_wait(iocb, orig_count);
182	if (ret < 0)
183		return ret;
184	file_accessed(iocb->ki_filp);
185
186	rreq = netfs_alloc_request(iocb->ki_filp->f_mapping, iocb->ki_filp,
187				   iocb->ki_pos, orig_count,
188				   iocb->ki_flags & IOCB_DIRECT ?
189				   NETFS_DIO_READ : NETFS_UNBUFFERED_READ);
190	if (IS_ERR(rreq))
191		return PTR_ERR(rreq);
192
193	netfs_stat(&netfs_n_rh_dio_read);
194	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_dio_read);
195
196	/* If this is an async op, we have to keep track of the destination
197	 * buffer for ourselves as the caller's iterator will be trashed when
198	 * we return.
199	 *
200	 * In such a case, extract an iterator to represent as much of the the
201	 * output buffer as we can manage.  Note that the extraction might not
202	 * be able to allocate a sufficiently large bvec array and may shorten
203	 * the request.
204	 */
205	if (user_backed_iter(iter)) {
206		ret = netfs_extract_user_iter(iter, rreq->len, &rreq->buffer.iter, 0);
207		if (ret < 0)
208			goto error_put;
209		rreq->direct_bv = (struct bio_vec *)rreq->buffer.iter.bvec;
210		rreq->direct_bv_count = ret;
211		rreq->direct_bv_unpin = iov_iter_extract_will_pin(iter);
212		rreq->len = iov_iter_count(&rreq->buffer.iter);
213	} else {
214		rreq->buffer.iter = *iter;
215		rreq->len = orig_count;
216		rreq->direct_bv_unpin = false;
217		iov_iter_advance(iter, orig_count);
218	}
219
220	// TODO: Set up bounce buffer if needed
221
222	if (!sync) {
223		rreq->iocb = iocb;
224		__set_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &rreq->flags);
225	}
226
227	ret = netfs_unbuffered_read(rreq, sync);
228	if (ret < 0)
229		goto out; /* May be -EIOCBQUEUED */
230	if (sync) {
231		// TODO: Copy from bounce buffer
232		iocb->ki_pos += rreq->transferred;
233		ret = rreq->transferred;
234	}
235
236out:
237	netfs_put_request(rreq, netfs_rreq_trace_put_return);
238	if (ret > 0)
239		orig_count -= ret;
240	return ret;
241
242error_put:
243	netfs_put_failed_request(rreq);
244	return ret;
245}
246EXPORT_SYMBOL(netfs_unbuffered_read_iter_locked);
247
248/**
249 * netfs_unbuffered_read_iter - Perform an unbuffered or direct I/O read
250 * @iocb: The I/O control descriptor describing the read
251 * @iter: The output buffer (also specifies read length)
252 *
253 * Perform an unbuffered I/O or direct I/O from the file in @iocb to the
254 * output buffer.  No use is made of the pagecache.
255 */
256ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter)
257{
258	struct inode *inode = file_inode(iocb->ki_filp);
259	ssize_t ret;
260
261	if (!iter->count)
262		return 0; /* Don't update atime */
263
264	ret = netfs_start_io_direct(inode);
265	if (ret == 0) {
266		ret = netfs_unbuffered_read_iter_locked(iocb, iter);
267		netfs_end_io_direct(inode);
268	}
269	return ret;
270}
271EXPORT_SYMBOL(netfs_unbuffered_read_iter);