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 */
 22static 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 */
 44static 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 */
 68int 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}
 90EXPORT_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 */
 99void netfs_end_io_read(struct inode *inode)
100	__releases(inode->i_rwsem)
101{
102	up_read(&inode->i_rwsem);
103}
104EXPORT_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 */
113int 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}
126EXPORT_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 */
135void netfs_end_io_write(struct inode *inode)
136	__releases(inode->i_rwsem)
137{
138	up_write(&inode->i_rwsem);
139}
140EXPORT_SYMBOL(netfs_end_io_write);
141
142/* Call with exclusively locked inode->i_rwsem */
143static 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 */
178int 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}
202EXPORT_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 */
211void netfs_end_io_direct(struct inode *inode)
212	__releases(inode->i_rwsem)
213{
214	up_read(&inode->i_rwsem);
215}
216EXPORT_SYMBOL(netfs_end_io_direct);