blob: 1fc5d1ce327e272c0878e8a53aa45b2dc96e97ad [file] [log] [blame]
Trond Myklebusta5864c92016-06-03 17:07:19 -04001/*
2 * Copyright (c) 2016 Trond Myklebust
3 *
4 * I/O and data path helper functionality.
5 */
6
7#include <linux/types.h>
8#include <linux/kernel.h>
9#include <linux/bitops.h>
10#include <linux/rwsem.h>
11#include <linux/fs.h>
12#include <linux/nfs_fs.h>
13
14#include "internal.h"
15
16/* Call with exclusively locked inode->i_rwsem */
17static void nfs_block_o_direct(struct nfs_inode *nfsi, struct inode *inode)
18{
19 if (test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
20 clear_bit(NFS_INO_ODIRECT, &nfsi->flags);
21 inode_dio_wait(inode);
22 }
23}
24
25/**
26 * nfs_start_io_read - declare the file is being used for buffered reads
27 * @inode - file inode
28 *
29 * Declare that a buffered read operation is about to start, and ensure
30 * that we block all direct I/O.
31 * On exit, the function ensures that the NFS_INO_ODIRECT flag is unset,
32 * and holds a shared lock on inode->i_rwsem to ensure that the flag
33 * cannot be changed.
34 * In practice, this means that buffered read operations are allowed to
35 * execute in parallel, thanks to the shared lock, whereas direct I/O
36 * operations need to wait to grab an exclusive lock in order to set
37 * NFS_INO_ODIRECT.
38 * Note that buffered writes and truncates both take a write lock on
39 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
40 */
41void
42nfs_start_io_read(struct inode *inode)
43{
44 struct nfs_inode *nfsi = NFS_I(inode);
45 /* Be an optimist! */
46 down_read(&inode->i_rwsem);
47 if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
48 return;
49 up_read(&inode->i_rwsem);
50 /* Slow path.... */
51 down_write(&inode->i_rwsem);
52 nfs_block_o_direct(nfsi, inode);
53 downgrade_write(&inode->i_rwsem);
54}
55
56/**
57 * nfs_end_io_read - declare that the buffered read operation is done
58 * @inode - file inode
59 *
60 * Declare that a buffered read operation is done, and release the shared
61 * lock on inode->i_rwsem.
62 */
63void
64nfs_end_io_read(struct inode *inode)
65{
66 up_read(&inode->i_rwsem);
67}
68
69/**
70 * nfs_start_io_write - declare the file is being used for buffered writes
71 * @inode - file inode
72 *
73 * Declare that a buffered read operation is about to start, and ensure
74 * that we block all direct I/O.
75 */
76void
77nfs_start_io_write(struct inode *inode)
78{
79 down_write(&inode->i_rwsem);
80 nfs_block_o_direct(NFS_I(inode), inode);
81}
82
83/**
84 * nfs_end_io_write - declare that the buffered write operation is done
85 * @inode - file inode
86 *
87 * Declare that a buffered write operation is done, and release the
88 * lock on inode->i_rwsem.
89 */
90void
91nfs_end_io_write(struct inode *inode)
92{
93 up_write(&inode->i_rwsem);
94}
95
96/* Call with exclusively locked inode->i_rwsem */
97static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
98{
99 if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
100 set_bit(NFS_INO_ODIRECT, &nfsi->flags);
101 nfs_wb_all(inode);
102 }
103}
104
105/**
106 * nfs_end_io_direct - declare the file is being used for direct i/o
107 * @inode - file inode
108 *
109 * Declare that a direct I/O operation is about to start, and ensure
110 * that we block all buffered I/O.
111 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
112 * and holds a shared lock on inode->i_rwsem to ensure that the flag
113 * cannot be changed.
114 * In practice, this means that direct I/O operations are allowed to
115 * execute in parallel, thanks to the shared lock, whereas buffered I/O
116 * operations need to wait to grab an exclusive lock in order to clear
117 * NFS_INO_ODIRECT.
118 * Note that buffered writes and truncates both take a write lock on
119 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
120 */
121void
122nfs_start_io_direct(struct inode *inode)
123{
124 struct nfs_inode *nfsi = NFS_I(inode);
125 /* Be an optimist! */
126 down_read(&inode->i_rwsem);
127 if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
128 return;
129 up_read(&inode->i_rwsem);
130 /* Slow path.... */
131 down_write(&inode->i_rwsem);
132 nfs_block_buffered(nfsi, inode);
133 downgrade_write(&inode->i_rwsem);
134}
135
136/**
137 * nfs_end_io_direct - declare that the direct i/o operation is done
138 * @inode - file inode
139 *
140 * Declare that a direct I/O operation is done, and release the shared
141 * lock on inode->i_rwsem.
142 */
143void
144nfs_end_io_direct(struct inode *inode)
145{
146 up_read(&inode->i_rwsem);
147}