Linux kernel mirror (for testing)
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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/**
18 * nfs_start_io_read - declare the file is being used for buffered reads
19 * @inode: file inode
20 *
21 * Declare that a buffered read operation is about to start, and ensure
22 * that we block all direct I/O.
23 * On exit, the function ensures that the NFS_INO_ODIRECT flag is unset,
24 * and holds a shared lock on inode->i_rwsem to ensure that the flag
25 * cannot be changed.
26 * In practice, this means that buffered read operations are allowed to
27 * execute in parallel, thanks to the shared lock, whereas direct I/O
28 * operations need to wait to grab an exclusive lock in order to set
29 * NFS_INO_ODIRECT.
30 * Note that buffered writes and truncates both take a write lock on
31 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
32 */
33int
34nfs_start_io_read(struct inode *inode)
35{
36 struct nfs_inode *nfsi = NFS_I(inode);
37 int err;
38
39 /* Be an optimist! */
40 err = down_read_killable(&inode->i_rwsem);
41 if (err)
42 return err;
43 if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
44 return 0;
45 up_read(&inode->i_rwsem);
46
47 /* Slow path.... */
48 err = down_write_killable(&inode->i_rwsem);
49 if (err)
50 return err;
51 nfs_file_block_o_direct(nfsi);
52 downgrade_write(&inode->i_rwsem);
53
54 return 0;
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 */
77int
78nfs_start_io_write(struct inode *inode)
79{
80 int err;
81
82 err = down_write_killable(&inode->i_rwsem);
83 if (!err)
84 nfs_file_block_o_direct(NFS_I(inode));
85 return err;
86}
87
88/**
89 * nfs_end_io_write - declare that the buffered write operation is done
90 * @inode: file inode
91 *
92 * Declare that a buffered write operation is done, and release the
93 * lock on inode->i_rwsem.
94 */
95void
96nfs_end_io_write(struct inode *inode)
97{
98 up_write(&inode->i_rwsem);
99}
100
101/* Call with exclusively locked inode->i_rwsem */
102static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
103{
104 if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
105 set_bit(NFS_INO_ODIRECT, &nfsi->flags);
106 nfs_sync_mapping(inode->i_mapping);
107 }
108}
109
110/**
111 * nfs_start_io_direct - declare the file is being used for direct i/o
112 * @inode: file inode
113 *
114 * Declare that a direct I/O operation is about to start, and ensure
115 * that we block all buffered I/O.
116 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
117 * and holds a shared lock on inode->i_rwsem to ensure that the flag
118 * cannot be changed.
119 * In practice, this means that direct I/O operations are allowed to
120 * execute in parallel, thanks to the shared lock, whereas buffered I/O
121 * operations need to wait to grab an exclusive lock in order to clear
122 * NFS_INO_ODIRECT.
123 * Note that buffered writes and truncates both take a write lock on
124 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
125 */
126int
127nfs_start_io_direct(struct inode *inode)
128{
129 struct nfs_inode *nfsi = NFS_I(inode);
130 int err;
131
132 /* Be an optimist! */
133 err = down_read_killable(&inode->i_rwsem);
134 if (err)
135 return err;
136 if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
137 return 0;
138 up_read(&inode->i_rwsem);
139
140 /* Slow path.... */
141 err = down_write_killable(&inode->i_rwsem);
142 if (err)
143 return err;
144 nfs_block_buffered(nfsi, inode);
145 downgrade_write(&inode->i_rwsem);
146
147 return 0;
148}
149
150/**
151 * nfs_end_io_direct - declare that the direct i/o operation is done
152 * @inode: file inode
153 *
154 * Declare that a direct I/O operation is done, and release the shared
155 * lock on inode->i_rwsem.
156 */
157void
158nfs_end_io_direct(struct inode *inode)
159{
160 up_read(&inode->i_rwsem);
161}