1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (c) 2016 Trond Myklebust
4 * Copyright (c) 2019 Jeff Layton
5 *
6 * I/O and data path helper functionality.
7 *
8 * Heavily borrowed from equivalent code in fs/nfs/io.c
9 */
10
11 #include <linux/ceph/ceph_debug.h>
12
13 #include <linux/types.h>
14 #include <linux/kernel.h>
15 #include <linux/rwsem.h>
16 #include <linux/fs.h>
17
18 #include "super.h"
19 #include "io.h"
20
21 /* Call with exclusively locked inode->i_rwsem */
22 static void ceph_block_o_direct(struct ceph_inode_info *ci, struct inode *inode)
23 {
24 lockdep_assert_held_write(&inode->i_rwsem);
25
26 if (READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT) {
27 spin_lock(&ci->i_ceph_lock);
28 ci->i_ceph_flags &= ~CEPH_I_ODIRECT;
29 spin_unlock(&ci->i_ceph_lock);
30 inode_dio_wait(inode);
31 }
32 }
33
34 /**
35 * ceph_start_io_read - declare the file is being used for buffered reads
36 * @inode: file inode
37 *
38 * Declare that a buffered read operation is about to start, and ensure
39 * that we block all direct I/O.
40 * On exit, the function ensures that the CEPH_I_ODIRECT flag is unset,
41 * and holds a shared lock on inode->i_rwsem to ensure that the flag
42 * cannot be changed.
43 * In practice, this means that buffered read operations are allowed to
44 * execute in parallel, thanks to the shared lock, whereas direct I/O
45 * operations need to wait to grab an exclusive lock in order to set
46 * CEPH_I_ODIRECT.
47 * Note that buffered writes and truncates both take a write lock on
48 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
49 */
50 void
51 ceph_start_io_read(struct inode *inode)
52 {
53 struct ceph_inode_info *ci = ceph_inode(inode);
54
55 /* Be an optimist! */
56 down_read(&inode->i_rwsem);
57 if (!(READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT))
58 return;
59 up_read(&inode->i_rwsem);
60 /* Slow path.... */
61 down_write(&inode->i_rwsem);
62 ceph_block_o_direct(ci, inode);
63 downgrade_write(&inode->i_rwsem);
64 }
65
66 /**
67 * ceph_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
74 ceph_end_io_read(struct inode *inode)
75 {
76 up_read(&inode->i_rwsem);
77 }
78
79 /**
80 * ceph_start_io_write - declare the file is being used for buffered writes
81 * @inode: file inode
82 *
83 * Declare that a buffered write operation is about to start, and ensure
84 * that we block all direct I/O.
85 */
86 void
87 ceph_start_io_write(struct inode *inode)
88 {
89 down_write(&inode->i_rwsem);
90 ceph_block_o_direct(ceph_inode(inode), inode);
91 }
92
93 /**
94 * ceph_end_io_write - declare that the buffered write operation is done
95 * @inode: file inode
96 *
97 * Declare that a buffered write operation is done, and release the
98 * lock on inode->i_rwsem.
99 */
100 void
101 ceph_end_io_write(struct inode *inode)
102 {
103 up_write(&inode->i_rwsem);
104 }
105
106 /* Call with exclusively locked inode->i_rwsem */
107 static void ceph_block_buffered(struct ceph_inode_info *ci, struct inode *inode)
108 {
109 lockdep_assert_held_write(&inode->i_rwsem);
110
111 if (!(READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT)) {
112 spin_lock(&ci->i_ceph_lock);
113 ci->i_ceph_flags |= CEPH_I_ODIRECT;
114 spin_unlock(&ci->i_ceph_lock);
115 /* FIXME: unmap_mapping_range? */
116 filemap_write_and_wait(inode->i_mapping);
117 }
118 }
119
120 /**
121 * ceph_end_io_direct - declare the file is being used for direct i/o
122 * @inode: file inode
123 *
124 * Declare that a direct I/O operation is about to start, and ensure
125 * that we block all buffered I/O.
126 * On exit, the function ensures that the CEPH_I_ODIRECT flag is set,
127 * and holds a shared lock on inode->i_rwsem to ensure that the flag
128 * cannot be changed.
129 * In practice, this means that direct I/O operations are allowed to
130 * execute in parallel, thanks to the shared lock, whereas buffered I/O
131 * operations need to wait to grab an exclusive lock in order to clear
132 * CEPH_I_ODIRECT.
133 * Note that buffered writes and truncates both take a write lock on
134 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
135 */
136 void
137 ceph_start_io_direct(struct inode *inode)
138 {
139 struct ceph_inode_info *ci = ceph_inode(inode);
140
141 /* Be an optimist! */
142 down_read(&inode->i_rwsem);
143 if (READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT)
144 return;
145 up_read(&inode->i_rwsem);
146 /* Slow path.... */
147 down_write(&inode->i_rwsem);
148 ceph_block_buffered(ci, inode);
149 downgrade_write(&inode->i_rwsem);
150 }
151
152 /**
153 * ceph_end_io_direct - declare that the direct i/o operation is done
154 * @inode: file inode
155 *
156 * Declare that a direct I/O operation is done, and release the shared
157 * lock on inode->i_rwsem.
158 */
159 void
160 ceph_end_io_direct(struct inode *inode)
161 {
162 up_read(&inode->i_rwsem);
163 }