1/*
  2 * Copyright (c) 2016 Trond Myklebust
  3 *
  4 * I/O and data path helper functionality.
  5 */
  6
  7#include <linux/types.h>
  8#include <linux/kernel.h>
  9#include <linux/bitops.h>
 10#include <linux/rwsem.h>
 11#include <linux/fs.h>
 12#include <linux/nfs_fs.h>
 13
 14#include "internal.h"
 15
 16/* Call with exclusively locked inode->i_rwsem */
 17static void nfs_block_o_direct(struct nfs_inode *nfsi, struct inode *inode)
 18{
 19	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
 20		clear_bit(NFS_INO_ODIRECT, &nfsi->flags);
 21		inode_dio_wait(inode);
 22	}
 23}
 24
 25/**
 26 * nfs_start_io_read - declare the file is being used for buffered reads
 27 * @inode - file inode
 28 *
 29 * Declare that a buffered read operation is about to start, and ensure
 30 * that we block all direct I/O.
 31 * On exit, the function ensures that the NFS_INO_ODIRECT flag is unset,
 32 * and holds a shared lock on inode->i_rwsem to ensure that the flag
 33 * cannot be changed.
 34 * In practice, this means that buffered read operations are allowed to
 35 * execute in parallel, thanks to the shared lock, whereas direct I/O
 36 * operations need to wait to grab an exclusive lock in order to set
 37 * NFS_INO_ODIRECT.
 38 * Note that buffered writes and truncates both take a write lock on
 39 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
 40 */
 41void
 42nfs_start_io_read(struct inode *inode)
 43{
 44	struct nfs_inode *nfsi = NFS_I(inode);
 45	/* Be an optimist! */
 46	down_read(&inode->i_rwsem);
 47	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
 48		return;
 49	up_read(&inode->i_rwsem);
 50	/* Slow path.... */
 51	down_write(&inode->i_rwsem);
 52	nfs_block_o_direct(nfsi, inode);
 53	downgrade_write(&inode->i_rwsem);
 54}
 55
 56/**
 57 * nfs_end_io_read - declare that the buffered read operation is done
 58 * @inode - file inode
 59 *
 60 * Declare that a buffered read operation is done, and release the shared
 61 * lock on inode->i_rwsem.
 62 */
 63void
 64nfs_end_io_read(struct inode *inode)
 65{
 66	up_read(&inode->i_rwsem);
 67}
 68
 69/**
 70 * nfs_start_io_write - declare the file is being used for buffered writes
 71 * @inode - file inode
 72 *
 73 * Declare that a buffered read operation is about to start, and ensure
 74 * that we block all direct I/O.
 75 */
 76void
 77nfs_start_io_write(struct inode *inode)
 78{
 79	down_write(&inode->i_rwsem);
 80	nfs_block_o_direct(NFS_I(inode), inode);
 81}
 82
 83/**
 84 * nfs_end_io_write - declare that the buffered write operation is done
 85 * @inode - file inode
 86 *
 87 * Declare that a buffered write operation is done, and release the
 88 * lock on inode->i_rwsem.
 89 */
 90void
 91nfs_end_io_write(struct inode *inode)
 92{
 93	up_write(&inode->i_rwsem);
 94}
 95
 96/* Call with exclusively locked inode->i_rwsem */
 97static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
 98{
 99	if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
100		set_bit(NFS_INO_ODIRECT, &nfsi->flags);
101		nfs_wb_all(inode);
102	}
103}
104
105/**
106 * nfs_end_io_direct - declare the file is being used for direct i/o
107 * @inode - file inode
108 *
109 * Declare that a direct I/O operation is about to start, and ensure
110 * that we block all buffered I/O.
111 * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
112 * and holds a shared lock on inode->i_rwsem to ensure that the flag
113 * cannot be changed.
114 * In practice, this means that direct I/O operations are allowed to
115 * execute in parallel, thanks to the shared lock, whereas buffered I/O
116 * operations need to wait to grab an exclusive lock in order to clear
117 * NFS_INO_ODIRECT.
118 * Note that buffered writes and truncates both take a write lock on
119 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
120 */
121void
122nfs_start_io_direct(struct inode *inode)
123{
124	struct nfs_inode *nfsi = NFS_I(inode);
125	/* Be an optimist! */
126	down_read(&inode->i_rwsem);
127	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
128		return;
129	up_read(&inode->i_rwsem);
130	/* Slow path.... */
131	down_write(&inode->i_rwsem);
132	nfs_block_buffered(nfsi, inode);
133	downgrade_write(&inode->i_rwsem);
134}
135
136/**
137 * nfs_end_io_direct - declare that the direct i/o operation is done
138 * @inode - file inode
139 *
140 * Declare that a direct I/O operation is done, and release the shared
141 * lock on inode->i_rwsem.
142 */
143void
144nfs_end_io_direct(struct inode *inode)
145{
146	up_read(&inode->i_rwsem);
147}