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 */
29 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
93 out:
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 EXPORT_SYMBOL(netfs_unbuffered_read_iter_locked);
102
103 /**
104 * netfs_unbuffered_read_iter - Perform an unbuffered or direct I/O read
105 * @iocb: The I/O control descriptor describing the read
106 * @iter: The output buffer (also specifies read length)
107 *
108 * Perform an unbuffered I/O or direct I/O from the file in @iocb to the
109 * output buffer. No use is made of the pagecache.
110 */
111 ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter)
112 {
113 struct inode *inode = file_inode(iocb->ki_filp);
114 ssize_t ret;
115
116 if (!iter->count)
117 return 0; /* Don't update atime */
118
119 ret = netfs_start_io_direct(inode);
120 if (ret == 0) {
121 ret = netfs_unbuffered_read_iter_locked(iocb, iter);
122 netfs_end_io_direct(inode);
123 }
124 return ret;
125 }
126 EXPORT_SYMBOL(netfs_unbuffered_read_iter);
127
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.