summaryrefslogtreecommitdiff
path: root/fs/nfs/io.c
blob: 1fc5d1ce327e272c0878e8a53aa45b2dc96e97ad (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
/*
 * Copyright (c) 2016 Trond Myklebust
 *
 * I/O and data path helper functionality.
 */

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/bitops.h>
#include <linux/rwsem.h>
#include <linux/fs.h>
#include <linux/nfs_fs.h>

#include "internal.h"

/* Call with exclusively locked inode->i_rwsem */
static void nfs_block_o_direct(struct nfs_inode *nfsi, struct inode *inode)
{
	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
		clear_bit(NFS_INO_ODIRECT, &nfsi->flags);
		inode_dio_wait(inode);
	}
}

/**
 * nfs_start_io_read - declare the file is being used for buffered reads
 * @inode - file inode
 *
 * Declare that a buffered read operation is about to start, and ensure
 * that we block all direct I/O.
 * On exit, the function ensures that the NFS_INO_ODIRECT flag is unset,
 * and holds a shared lock on inode->i_rwsem to ensure that the flag
 * cannot be changed.
 * In practice, this means that buffered read operations are allowed to
 * execute in parallel, thanks to the shared lock, whereas direct I/O
 * operations need to wait to grab an exclusive lock in order to set
 * NFS_INO_ODIRECT.
 * Note that buffered writes and truncates both take a write lock on
 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
 */
void
nfs_start_io_read(struct inode *inode)
{
	struct nfs_inode *nfsi = NFS_I(inode);
	/* Be an optimist! */
	down_read(&inode->i_rwsem);
	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
		return;
	up_read(&inode->i_rwsem);
	/* Slow path.... */
	down_write(&inode->i_rwsem);
	nfs_block_o_direct(nfsi, inode);
	downgrade_write(&inode->i_rwsem);
}

/**
 * nfs_end_io_read - declare that the buffered read operation is done
 * @inode - file inode
 *
 * Declare that a buffered read operation is done, and release the shared
 * lock on inode->i_rwsem.
 */
void
nfs_end_io_read(struct inode *inode)
{
	up_read(&inode->i_rwsem);
}

/**
 * nfs_start_io_write - declare the file is being used for buffered writes
 * @inode - file inode
 *
 * Declare that a buffered read operation is about to start, and ensure
 * that we block all direct I/O.
 */
void
nfs_start_io_write(struct inode *inode)
{
	down_write(&inode->i_rwsem);
	nfs_block_o_direct(NFS_I(inode), inode);
}

/**
 * nfs_end_io_write - declare that the buffered write operation is done
 * @inode - file inode
 *
 * Declare that a buffered write operation is done, and release the
 * lock on inode->i_rwsem.
 */
void
nfs_end_io_write(struct inode *inode)
{
	up_write(&inode->i_rwsem);
}

/* Call with exclusively locked inode->i_rwsem */
static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
{
	if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
		set_bit(NFS_INO_ODIRECT, &nfsi->flags);
		nfs_wb_all(inode);
	}
}

/**
 * nfs_end_io_direct - declare the file is being used for direct i/o
 * @inode - file inode
 *
 * Declare that a direct I/O operation is about to start, and ensure
 * that we block all buffered I/O.
 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
 * and holds a shared lock on inode->i_rwsem to ensure that the flag
 * cannot be changed.
 * In practice, this means that direct I/O operations are allowed to
 * execute in parallel, thanks to the shared lock, whereas buffered I/O
 * operations need to wait to grab an exclusive lock in order to clear
 * NFS_INO_ODIRECT.
 * Note that buffered writes and truncates both take a write lock on
 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
 */
void
nfs_start_io_direct(struct inode *inode)
{
	struct nfs_inode *nfsi = NFS_I(inode);
	/* Be an optimist! */
	down_read(&inode->i_rwsem);
	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
		return;
	up_read(&inode->i_rwsem);
	/* Slow path.... */
	down_write(&inode->i_rwsem);
	nfs_block_buffered(nfsi, inode);
	downgrade_write(&inode->i_rwsem);
}

/**
 * nfs_end_io_direct - declare that the direct i/o operation is done
 * @inode - file inode
 *
 * Declare that a direct I/O operation is done, and release the shared
 * lock on inode->i_rwsem.
 */
void
nfs_end_io_direct(struct inode *inode)
{
	up_read(&inode->i_rwsem);
}