1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (c) 2016 Trond Myklebust
  4 *
  5 * I/O and data path helper functionality.
  6 */
  7
  8#include <linux/types.h>
  9#include <linux/kernel.h>
 10#include <linux/bitops.h>
 11#include <linux/rwsem.h>
 12#include <linux/fs.h>
 13#include <linux/nfs_fs.h>
 14
 15#include "internal.h"
 16
 17/* Call with exclusively locked inode->i_rwsem */
 18static void nfs_block_o_direct(struct nfs_inode *nfsi, struct inode *inode)
 19{
 20	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
 21		clear_bit(NFS_INO_ODIRECT, &nfsi->flags);
 22		inode_dio_wait(inode);
 23	}
 24}
 25
 26/**
 27 * nfs_start_io_read - declare the file is being used for buffered reads
 28 * @inode: file inode
 29 *
 30 * Declare that a buffered read operation is about to start, and ensure
 31 * that we block all direct I/O.
 32 * On exit, the function ensures that the NFS_INO_ODIRECT flag is unset,
 33 * and holds a shared lock on inode->i_rwsem to ensure that the flag
 34 * cannot be changed.
 35 * In practice, this means that buffered read operations are allowed to
 36 * execute in parallel, thanks to the shared lock, whereas direct I/O
 37 * operations need to wait to grab an exclusive lock in order to set
 38 * NFS_INO_ODIRECT.
 39 * Note that buffered writes and truncates both take a write lock on
 40 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
 41 */
 42int
 43nfs_start_io_read(struct inode *inode)
 44{
 45	struct nfs_inode *nfsi = NFS_I(inode);
 46	int err;
 47
 48	/* Be an optimist! */
 49	err = down_read_killable(&inode->i_rwsem);
 50	if (err)
 51		return err;
 52	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
 53		return 0;
 54	up_read(&inode->i_rwsem);
 55
 56	/* Slow path.... */
 57	err = down_write_killable(&inode->i_rwsem);
 58	if (err)
 59		return err;
 60	nfs_block_o_direct(nfsi, inode);
 61	downgrade_write(&inode->i_rwsem);
 62
 63	return 0;
 64}
 65
 66/**
 67 * nfs_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 */
 73void
 74nfs_end_io_read(struct inode *inode)
 75{
 76	up_read(&inode->i_rwsem);
 77}
 78
 79/**
 80 * nfs_start_io_write - declare the file is being used for buffered writes
 81 * @inode: file inode
 82 *
 83 * Declare that a buffered read operation is about to start, and ensure
 84 * that we block all direct I/O.
 85 */
 86int
 87nfs_start_io_write(struct inode *inode)
 88{
 89	int err;
 90
 91	err = down_write_killable(&inode->i_rwsem);
 92	if (!err)
 93		nfs_block_o_direct(NFS_I(inode), inode);
 94	return err;
 95}
 96
 97/**
 98 * nfs_end_io_write - declare that the buffered write operation is done
 99 * @inode: file inode
100 *
101 * Declare that a buffered write operation is done, and release the
102 * lock on inode->i_rwsem.
103 */
104void
105nfs_end_io_write(struct inode *inode)
106{
107	up_write(&inode->i_rwsem);
108}
109
110/* Call with exclusively locked inode->i_rwsem */
111static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
112{
113	if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
114		set_bit(NFS_INO_ODIRECT, &nfsi->flags);
115		nfs_sync_mapping(inode->i_mapping);
116	}
117}
118
119/**
120 * nfs_start_io_direct - declare the file is being used for direct i/o
121 * @inode: file inode
122 *
123 * Declare that a direct I/O operation is about to start, and ensure
124 * that we block all buffered I/O.
125 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
126 * and holds a shared lock on inode->i_rwsem to ensure that the flag
127 * cannot be changed.
128 * In practice, this means that direct I/O operations are allowed to
129 * execute in parallel, thanks to the shared lock, whereas buffered I/O
130 * operations need to wait to grab an exclusive lock in order to clear
131 * NFS_INO_ODIRECT.
132 * Note that buffered writes and truncates both take a write lock on
133 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
134 */
135int
136nfs_start_io_direct(struct inode *inode)
137{
138	struct nfs_inode *nfsi = NFS_I(inode);
139	int err;
140
141	/* Be an optimist! */
142	err = down_read_killable(&inode->i_rwsem);
143	if (err)
144		return err;
145	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
146		return 0;
147	up_read(&inode->i_rwsem);
148
149	/* Slow path.... */
150	err = down_write_killable(&inode->i_rwsem);
151	if (err)
152		return err;
153	nfs_block_buffered(nfsi, inode);
154	downgrade_write(&inode->i_rwsem);
155
156	return 0;
157}
158
159/**
160 * nfs_end_io_direct - declare that the direct i/o operation is done
161 * @inode: file inode
162 *
163 * Declare that a direct I/O operation is done, and release the shared
164 * lock on inode->i_rwsem.
165 */
166void
167nfs_end_io_direct(struct inode *inode)
168{
169	up_read(&inode->i_rwsem);
170}