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 */
 42void
 43nfs_start_io_read(struct inode *inode)
 44{
 45	struct nfs_inode *nfsi = NFS_I(inode);
 46	/* Be an optimist! */
 47	down_read(&inode->i_rwsem);
 48	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
 49		return;
 50	up_read(&inode->i_rwsem);
 51	/* Slow path.... */
 52	down_write(&inode->i_rwsem);
 53	nfs_block_o_direct(nfsi, inode);
 54	downgrade_write(&inode->i_rwsem);
 55}
 56
 57/**
 58 * nfs_end_io_read - declare that the buffered read operation is done
 59 * @inode: file inode
 60 *
 61 * Declare that a buffered read operation is done, and release the shared
 62 * lock on inode->i_rwsem.
 63 */
 64void
 65nfs_end_io_read(struct inode *inode)
 66{
 67	up_read(&inode->i_rwsem);
 68}
 69
 70/**
 71 * nfs_start_io_write - declare the file is being used for buffered writes
 72 * @inode: file inode
 73 *
 74 * Declare that a buffered read operation is about to start, and ensure
 75 * that we block all direct I/O.
 76 */
 77void
 78nfs_start_io_write(struct inode *inode)
 79{
 80	down_write(&inode->i_rwsem);
 81	nfs_block_o_direct(NFS_I(inode), inode);
 82}
 83
 84/**
 85 * nfs_end_io_write - declare that the buffered write operation is done
 86 * @inode: file inode
 87 *
 88 * Declare that a buffered write operation is done, and release the
 89 * lock on inode->i_rwsem.
 90 */
 91void
 92nfs_end_io_write(struct inode *inode)
 93{
 94	up_write(&inode->i_rwsem);
 95}
 96
 97/* Call with exclusively locked inode->i_rwsem */
 98static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
 99{
100	if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
101		set_bit(NFS_INO_ODIRECT, &nfsi->flags);
102		nfs_sync_mapping(inode->i_mapping);
103	}
104}
105
106/**
107 * nfs_end_io_direct - declare the file is being used for direct i/o
108 * @inode: file inode
109 *
110 * Declare that a direct I/O operation is about to start, and ensure
111 * that we block all buffered I/O.
112 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
113 * and holds a shared lock on inode->i_rwsem to ensure that the flag
114 * cannot be changed.
115 * In practice, this means that direct I/O operations are allowed to
116 * execute in parallel, thanks to the shared lock, whereas buffered I/O
117 * operations need to wait to grab an exclusive lock in order to clear
118 * NFS_INO_ODIRECT.
119 * Note that buffered writes and truncates both take a write lock on
120 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
121 */
122void
123nfs_start_io_direct(struct inode *inode)
124{
125	struct nfs_inode *nfsi = NFS_I(inode);
126	/* Be an optimist! */
127	down_read(&inode->i_rwsem);
128	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
129		return;
130	up_read(&inode->i_rwsem);
131	/* Slow path.... */
132	down_write(&inode->i_rwsem);
133	nfs_block_buffered(nfsi, inode);
134	downgrade_write(&inode->i_rwsem);
135}
136
137/**
138 * nfs_end_io_direct - declare that the direct i/o operation is done
139 * @inode: file inode
140 *
141 * Declare that a direct I/O operation is done, and release the shared
142 * lock on inode->i_rwsem.
143 */
144void
145nfs_end_io_direct(struct inode *inode)
146{
147	up_read(&inode->i_rwsem);
148}