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 */
nfs_block_o_direct(struct nfs_inode * nfsi,struct inode * inode)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 int
nfs_start_io_read(struct inode * inode)43 nfs_start_io_read(struct inode *inode)
44 {
45 struct nfs_inode *nfsi = NFS_I(inode);
46 int err;
47
48 /* Be an optimist! */
49 err = down_read_killable(&inode->i_rwsem);
50 if (err)
51 return err;
52 if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
53 return 0;
54 up_read(&inode->i_rwsem);
55
56 /* Slow path.... */
57 err = down_write_killable(&inode->i_rwsem);
58 if (err)
59 return err;
60 nfs_block_o_direct(nfsi, inode);
61 downgrade_write(&inode->i_rwsem);
62
63 return 0;
64 }
65
66 /**
67 * nfs_end_io_read - declare that the buffered read operation is done
68 * @inode: file inode
69 *
70 * Declare that a buffered read operation is done, and release the shared
71 * lock on inode->i_rwsem.
72 */
73 void
nfs_end_io_read(struct inode * inode)74 nfs_end_io_read(struct inode *inode)
75 {
76 up_read(&inode->i_rwsem);
77 }
78
79 /**
80 * nfs_start_io_write - declare the file is being used for buffered writes
81 * @inode: file inode
82 *
83 * Declare that a buffered read operation is about to start, and ensure
84 * that we block all direct I/O.
85 */
86 int
nfs_start_io_write(struct inode * inode)87 nfs_start_io_write(struct inode *inode)
88 {
89 int err;
90
91 err = down_write_killable(&inode->i_rwsem);
92 if (!err)
93 nfs_block_o_direct(NFS_I(inode), inode);
94 return err;
95 }
96
97 /**
98 * nfs_end_io_write - declare that the buffered write operation is done
99 * @inode: file inode
100 *
101 * Declare that a buffered write operation is done, and release the
102 * lock on inode->i_rwsem.
103 */
104 void
nfs_end_io_write(struct inode * inode)105 nfs_end_io_write(struct inode *inode)
106 {
107 up_write(&inode->i_rwsem);
108 }
109
110 /* Call with exclusively locked inode->i_rwsem */
nfs_block_buffered(struct nfs_inode * nfsi,struct inode * inode)111 static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
112 {
113 if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
114 set_bit(NFS_INO_ODIRECT, &nfsi->flags);
115 nfs_sync_mapping(inode->i_mapping);
116 }
117 }
118
119 /**
120 * nfs_start_io_direct - declare the file is being used for direct i/o
121 * @inode: file inode
122 *
123 * Declare that a direct I/O operation is about to start, and ensure
124 * that we block all buffered I/O.
125 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
126 * and holds a shared lock on inode->i_rwsem to ensure that the flag
127 * cannot be changed.
128 * In practice, this means that direct I/O operations are allowed to
129 * execute in parallel, thanks to the shared lock, whereas buffered I/O
130 * operations need to wait to grab an exclusive lock in order to clear
131 * NFS_INO_ODIRECT.
132 * Note that buffered writes and truncates both take a write lock on
133 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
134 */
135 int
nfs_start_io_direct(struct inode * inode)136 nfs_start_io_direct(struct inode *inode)
137 {
138 struct nfs_inode *nfsi = NFS_I(inode);
139 int err;
140
141 /* Be an optimist! */
142 err = down_read_killable(&inode->i_rwsem);
143 if (err)
144 return err;
145 if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
146 return 0;
147 up_read(&inode->i_rwsem);
148
149 /* Slow path.... */
150 err = down_write_killable(&inode->i_rwsem);
151 if (err)
152 return err;
153 nfs_block_buffered(nfsi, inode);
154 downgrade_write(&inode->i_rwsem);
155
156 return 0;
157 }
158
159 /**
160 * nfs_end_io_direct - declare that the direct i/o operation is done
161 * @inode: file inode
162 *
163 * Declare that a direct I/O operation is done, and release the shared
164 * lock on inode->i_rwsem.
165 */
166 void
nfs_end_io_direct(struct inode * inode)167 nfs_end_io_direct(struct inode *inode)
168 {
169 up_read(&inode->i_rwsem);
170 }
171