1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * I/O and data path helper functionality.
4 *
5 * Borrowed from NFS Copyright (c) 2016 Trond Myklebust
6 */
7
8 #include <linux/kernel.h>
9 #include <linux/netfs.h>
10 #include "internal.h"
11
12 /*
13 * inode_dio_wait_interruptible - wait for outstanding DIO requests to finish
14 * @inode: inode to wait for
15 *
16 * Waits for all pending direct I/O requests to finish so that we can
17 * proceed with a truncate or equivalent operation.
18 *
19 * Must be called under a lock that serializes taking new references
20 * to i_dio_count, usually by inode->i_mutex.
21 */
22 static int inode_dio_wait_interruptible(struct inode *inode)
23 {
24 if (!atomic_read(&inode->i_dio_count))
25 return 0;
26
27 wait_queue_head_t *wq = bit_waitqueue(&inode->i_state, __I_DIO_WAKEUP);
28 DEFINE_WAIT_BIT(q, &inode->i_state, __I_DIO_WAKEUP);
29
30 for (;;) {
31 prepare_to_wait(wq, &q.wq_entry, TASK_INTERRUPTIBLE);
32 if (!atomic_read(&inode->i_dio_count))
33 break;
34 if (signal_pending(current))
35 break;
36 schedule();
37 }
38 finish_wait(wq, &q.wq_entry);
39
40 return atomic_read(&inode->i_dio_count) ? -ERESTARTSYS : 0;
41 }
42
43 /* Call with exclusively locked inode->i_rwsem */
44 static int netfs_block_o_direct(struct netfs_inode *ictx)
45 {
46 if (!test_bit(NETFS_ICTX_ODIRECT, &ictx->flags))
47 return 0;
48 clear_bit(NETFS_ICTX_ODIRECT, &ictx->flags);
49 return inode_dio_wait_interruptible(&ictx->inode);
50 }
51
52 /**
53 * netfs_start_io_read - declare the file is being used for buffered reads
54 * @inode: file inode
55 *
56 * Declare that a buffered read operation is about to start, and ensure
57 * that we block all direct I/O.
58 * On exit, the function ensures that the NETFS_ICTX_ODIRECT flag is unset,
59 * and holds a shared lock on inode->i_rwsem to ensure that the flag
60 * cannot be changed.
61 * In practice, this means that buffered read operations are allowed to
62 * execute in parallel, thanks to the shared lock, whereas direct I/O
63 * operations need to wait to grab an exclusive lock in order to set
64 * NETFS_ICTX_ODIRECT.
65 * Note that buffered writes and truncates both take a write lock on
66 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
67 */
68 int netfs_start_io_read(struct inode *inode)
69 __acquires(inode->i_rwsem)
70 {
71 struct netfs_inode *ictx = netfs_inode(inode);
72
73 /* Be an optimist! */
74 if (down_read_interruptible(&inode->i_rwsem) < 0)
75 return -ERESTARTSYS;
76 if (test_bit(NETFS_ICTX_ODIRECT, &ictx->flags) == 0)
77 return 0;
78 up_read(&inode->i_rwsem);
79
80 /* Slow path.... */
81 if (down_write_killable(&inode->i_rwsem) < 0)
82 return -ERESTARTSYS;
83 if (netfs_block_o_direct(ictx) < 0) {
84 up_write(&inode->i_rwsem);
85 return -ERESTARTSYS;
86 }
87 downgrade_write(&inode->i_rwsem);
88 return 0;
89 }
90 EXPORT_SYMBOL(netfs_start_io_read);
91
92 /**
93 * netfs_end_io_read - declare that the buffered read operation is done
94 * @inode: file inode
95 *
96 * Declare that a buffered read operation is done, and release the shared
97 * lock on inode->i_rwsem.
98 */
99 void netfs_end_io_read(struct inode *inode)
100 __releases(inode->i_rwsem)
101 {
102 up_read(&inode->i_rwsem);
103 }
104 EXPORT_SYMBOL(netfs_end_io_read);
105
106 /**
107 * netfs_start_io_write - declare the file is being used for buffered writes
108 * @inode: file inode
109 *
110 * Declare that a buffered read operation is about to start, and ensure
111 * that we block all direct I/O.
112 */
113 int netfs_start_io_write(struct inode *inode)
114 __acquires(inode->i_rwsem)
115 {
116 struct netfs_inode *ictx = netfs_inode(inode);
117
118 if (down_write_killable(&inode->i_rwsem) < 0)
119 return -ERESTARTSYS;
120 if (netfs_block_o_direct(ictx) < 0) {
121 up_write(&inode->i_rwsem);
122 return -ERESTARTSYS;
123 }
124 return 0;
125 }
126 EXPORT_SYMBOL(netfs_start_io_write);
127
128 /**
129 * netfs_end_io_write - declare that the buffered write operation is done
130 * @inode: file inode
131 *
132 * Declare that a buffered write operation is done, and release the
133 * lock on inode->i_rwsem.
134 */
135 void netfs_end_io_write(struct inode *inode)
136 __releases(inode->i_rwsem)
137 {
138 up_write(&inode->i_rwsem);
139 }
140 EXPORT_SYMBOL(netfs_end_io_write);
141
142 /* Call with exclusively locked inode->i_rwsem */
143 static int netfs_block_buffered(struct inode *inode)
144 {
145 struct netfs_inode *ictx = netfs_inode(inode);
146 int ret;
147
148 if (!test_bit(NETFS_ICTX_ODIRECT, &ictx->flags)) {
149 set_bit(NETFS_ICTX_ODIRECT, &ictx->flags);
150 if (inode->i_mapping->nrpages != 0) {
151 unmap_mapping_range(inode->i_mapping, 0, 0, 0);
152 ret = filemap_fdatawait(inode->i_mapping);
153 if (ret < 0) {
154 clear_bit(NETFS_ICTX_ODIRECT, &ictx->flags);
155 return ret;
156 }
157 }
158 }
159 return 0;
160 }
161
162 /**
163 * netfs_start_io_direct - declare the file is being used for direct i/o
164 * @inode: file inode
165 *
166 * Declare that a direct I/O operation is about to start, and ensure
167 * that we block all buffered I/O.
168 * On exit, the function ensures that the NETFS_ICTX_ODIRECT flag is set,
169 * and holds a shared lock on inode->i_rwsem to ensure that the flag
170 * cannot be changed.
171 * In practice, this means that direct I/O operations are allowed to
172 * execute in parallel, thanks to the shared lock, whereas buffered I/O
173 * operations need to wait to grab an exclusive lock in order to clear
174 * NETFS_ICTX_ODIRECT.
175 * Note that buffered writes and truncates both take a write lock on
176 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
177 */
178 int netfs_start_io_direct(struct inode *inode)
179 __acquires(inode->i_rwsem)
180 {
181 struct netfs_inode *ictx = netfs_inode(inode);
182 int ret;
183
184 /* Be an optimist! */
185 if (down_read_interruptible(&inode->i_rwsem) < 0)
186 return -ERESTARTSYS;
187 if (test_bit(NETFS_ICTX_ODIRECT, &ictx->flags) != 0)
188 return 0;
189 up_read(&inode->i_rwsem);
190
191 /* Slow path.... */
192 if (down_write_killable(&inode->i_rwsem) < 0)
193 return -ERESTARTSYS;
194 ret = netfs_block_buffered(inode);
195 if (ret < 0) {
196 up_write(&inode->i_rwsem);
197 return ret;
198 }
199 downgrade_write(&inode->i_rwsem);
200 return 0;
201 }
202 EXPORT_SYMBOL(netfs_start_io_direct);
203
204 /**
205 * netfs_end_io_direct - declare that the direct i/o operation is done
206 * @inode: file inode
207 *
208 * Declare that a direct I/O operation is done, and release the shared
209 * lock on inode->i_rwsem.
210 */
211 void netfs_end_io_direct(struct inode *inode)
212 __releases(inode->i_rwsem)
213 {
214 up_read(&inode->i_rwsem);
215 }
216 EXPORT_SYMBOL(netfs_end_io_direct);
217
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