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 */
18 static 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 */
42 void
43 nfs_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 */
64 void
65 nfs_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 */
77 void
78 nfs_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 */
91 void
92 nfs_end_io_write(struct inode *inode)
93 {
94 up_write(&inode->i_rwsem);
95 }
96
97 /* Call with exclusively locked inode->i_rwsem */
98 static 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_end_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 */
122 void
123 nfs_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 */
144 void
145 nfs_end_io_direct(struct inode *inode)
146 {
147 up_read(&inode->i_rwsem);
148 }