1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (c) 2016 Trond Myklebust
4 *
5 * I/O and data path helper functionality.
6 */
7
8#include <linux/types.h>
9#include <linux/kernel.h>
10#include <linux/bitops.h>
11#include <linux/rwsem.h>
12#include <linux/fs.h>
13#include <linux/nfs_fs.h>
14
15#include "internal.h"
16
17/* Call with exclusively locked inode->i_rwsem */
18static void nfs_block_o_direct(struct nfs_inode *nfsi, struct inode *inode)
19{
20	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
21		clear_bit(NFS_INO_ODIRECT, &nfsi->flags);
22		inode_dio_wait(inode);
23	}
24}
25
26/**
27 * nfs_start_io_read - declare the file is being used for buffered reads
28 * @inode: file inode
29 *
30 * Declare that a buffered read operation is about to start, and ensure
31 * that we block all direct I/O.
32 * On exit, the function ensures that the NFS_INO_ODIRECT flag is unset,
33 * and holds a shared lock on inode->i_rwsem to ensure that the flag
34 * cannot be changed.
35 * In practice, this means that buffered read operations are allowed to
36 * execute in parallel, thanks to the shared lock, whereas direct I/O
37 * operations need to wait to grab an exclusive lock in order to set
38 * NFS_INO_ODIRECT.
39 * Note that buffered writes and truncates both take a write lock on
40 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
41 */
42void
43nfs_start_io_read(struct inode *inode)
44{
45	struct nfs_inode *nfsi = NFS_I(inode);
46	/* Be an optimist! */
47	down_read(&inode->i_rwsem);
48	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
49		return;
50	up_read(&inode->i_rwsem);
51	/* Slow path.... */
52	down_write(&inode->i_rwsem);
53	nfs_block_o_direct(nfsi, inode);
54	downgrade_write(&inode->i_rwsem);
55}
56
57/**
58 * nfs_end_io_read - declare that the buffered read operation is done
59 * @inode: file inode
60 *
61 * Declare that a buffered read operation is done, and release the shared
62 * lock on inode->i_rwsem.
63 */
64void
65nfs_end_io_read(struct inode *inode)
66{
67	up_read(&inode->i_rwsem);
68}
69
70/**
71 * nfs_start_io_write - declare the file is being used for buffered writes
72 * @inode: file inode
73 *
74 * Declare that a buffered read operation is about to start, and ensure
75 * that we block all direct I/O.
76 */
77void
78nfs_start_io_write(struct inode *inode)
79{
80	down_write(&inode->i_rwsem);
81	nfs_block_o_direct(NFS_I(inode), inode);
82}
83
84/**
85 * nfs_end_io_write - declare that the buffered write operation is done
86 * @inode: file inode
87 *
88 * Declare that a buffered write operation is done, and release the
89 * lock on inode->i_rwsem.
90 */
91void
92nfs_end_io_write(struct inode *inode)
93{
94	up_write(&inode->i_rwsem);
95}
96
97/* Call with exclusively locked inode->i_rwsem */
98static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
99{
100	if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
101		set_bit(NFS_INO_ODIRECT, &nfsi->flags);
102		nfs_sync_mapping(inode->i_mapping);
103	}
104}
105
106/**
107 * nfs_start_io_direct - declare the file is being used for direct i/o
108 * @inode: file inode
109 *
110 * Declare that a direct I/O operation is about to start, and ensure
111 * that we block all buffered I/O.
112 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
113 * and holds a shared lock on inode->i_rwsem to ensure that the flag
114 * cannot be changed.
115 * In practice, this means that direct I/O operations are allowed to
116 * execute in parallel, thanks to the shared lock, whereas buffered I/O
117 * operations need to wait to grab an exclusive lock in order to clear
118 * NFS_INO_ODIRECT.
119 * Note that buffered writes and truncates both take a write lock on
120 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
121 */
122void
123nfs_start_io_direct(struct inode *inode)
124{
125	struct nfs_inode *nfsi = NFS_I(inode);
126	/* Be an optimist! */
127	down_read(&inode->i_rwsem);
128	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
129		return;
130	up_read(&inode->i_rwsem);
131	/* Slow path.... */
132	down_write(&inode->i_rwsem);
133	nfs_block_buffered(nfsi, inode);
134	downgrade_write(&inode->i_rwsem);
135}
136
137/**
138 * nfs_end_io_direct - declare that the direct i/o operation is done
139 * @inode: file inode
140 *
141 * Declare that a direct I/O operation is done, and release the shared
142 * lock on inode->i_rwsem.
143 */
144void
145nfs_end_io_direct(struct inode *inode)
146{
147	up_read(&inode->i_rwsem);
148}
149