1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (c) 2016 Trond Myklebust
  4 * Copyright (c) 2019 Jeff Layton
  5 *
  6 * I/O and data path helper functionality.
  7 *
  8 * Heavily borrowed from equivalent code in fs/nfs/io.c
  9 */
 10
 11#include <linux/ceph/ceph_debug.h>
 12
 13#include <linux/types.h>
 14#include <linux/kernel.h>
 15#include <linux/rwsem.h>
 16#include <linux/fs.h>
 17
 18#include "super.h"
 19#include "io.h"
 20
 21/* Call with exclusively locked inode->i_rwsem */
 22static void ceph_block_o_direct(struct ceph_inode_info *ci, struct inode *inode)
 23{
 24	lockdep_assert_held_write(&inode->i_rwsem);
 25
 26	if (READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT) {
 27		spin_lock(&ci->i_ceph_lock);
 28		ci->i_ceph_flags &= ~CEPH_I_ODIRECT;
 29		spin_unlock(&ci->i_ceph_lock);
 30		inode_dio_wait(inode);
 31	}
 32}
 33
 34/**
 35 * ceph_start_io_read - declare the file is being used for buffered reads
 36 * @inode: file inode
 37 *
 38 * Declare that a buffered read operation is about to start, and ensure
 39 * that we block all direct I/O.
 40 * On exit, the function ensures that the CEPH_I_ODIRECT flag is unset,
 41 * and holds a shared lock on inode->i_rwsem to ensure that the flag
 42 * cannot be changed.
 43 * In practice, this means that buffered read operations are allowed to
 44 * execute in parallel, thanks to the shared lock, whereas direct I/O
 45 * operations need to wait to grab an exclusive lock in order to set
 46 * CEPH_I_ODIRECT.
 47 * Note that buffered writes and truncates both take a write lock on
 48 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
 49 */
 50void
 51ceph_start_io_read(struct inode *inode)
 52{
 53	struct ceph_inode_info *ci = ceph_inode(inode);
 54
 55	/* Be an optimist! */
 56	down_read(&inode->i_rwsem);
 57	if (!(READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT))
 58		return;
 59	up_read(&inode->i_rwsem);
 60	/* Slow path.... */
 61	down_write(&inode->i_rwsem);
 62	ceph_block_o_direct(ci, inode);
 63	downgrade_write(&inode->i_rwsem);
 64}
 65
 66/**
 67 * ceph_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
 74ceph_end_io_read(struct inode *inode)
 75{
 76	up_read(&inode->i_rwsem);
 77}
 78
 79/**
 80 * ceph_start_io_write - declare the file is being used for buffered writes
 81 * @inode: file inode
 82 *
 83 * Declare that a buffered write operation is about to start, and ensure
 84 * that we block all direct I/O.
 85 */
 86void
 87ceph_start_io_write(struct inode *inode)
 88{
 89	down_write(&inode->i_rwsem);
 90	ceph_block_o_direct(ceph_inode(inode), inode);
 91}
 92
 93/**
 94 * ceph_end_io_write - declare that the buffered write operation is done
 95 * @inode: file inode
 96 *
 97 * Declare that a buffered write operation is done, and release the
 98 * lock on inode->i_rwsem.
 99 */
100void
101ceph_end_io_write(struct inode *inode)
102{
103	up_write(&inode->i_rwsem);
104}
105
106/* Call with exclusively locked inode->i_rwsem */
107static void ceph_block_buffered(struct ceph_inode_info *ci, struct inode *inode)
108{
109	lockdep_assert_held_write(&inode->i_rwsem);
110
111	if (!(READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT)) {
112		spin_lock(&ci->i_ceph_lock);
113		ci->i_ceph_flags |= CEPH_I_ODIRECT;
114		spin_unlock(&ci->i_ceph_lock);
115		/* FIXME: unmap_mapping_range? */
116		filemap_write_and_wait(inode->i_mapping);
117	}
118}
119
120/**
121 * ceph_end_io_direct - declare the file is being used for direct i/o
122 * @inode: file inode
123 *
124 * Declare that a direct I/O operation is about to start, and ensure
125 * that we block all buffered I/O.
126 * On exit, the function ensures that the CEPH_I_ODIRECT flag is set,
127 * and holds a shared lock on inode->i_rwsem to ensure that the flag
128 * cannot be changed.
129 * In practice, this means that direct I/O operations are allowed to
130 * execute in parallel, thanks to the shared lock, whereas buffered I/O
131 * operations need to wait to grab an exclusive lock in order to clear
132 * CEPH_I_ODIRECT.
133 * Note that buffered writes and truncates both take a write lock on
134 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
135 */
136void
137ceph_start_io_direct(struct inode *inode)
138{
139	struct ceph_inode_info *ci = ceph_inode(inode);
140
141	/* Be an optimist! */
142	down_read(&inode->i_rwsem);
143	if (READ_ONCE(ci->i_ceph_flags) & CEPH_I_ODIRECT)
144		return;
145	up_read(&inode->i_rwsem);
146	/* Slow path.... */
147	down_write(&inode->i_rwsem);
148	ceph_block_buffered(ci, inode);
149	downgrade_write(&inode->i_rwsem);
150}
151
152/**
153 * ceph_end_io_direct - declare that the direct i/o operation is done
154 * @inode: file inode
155 *
156 * Declare that a direct I/O operation is done, and release the shared
157 * lock on inode->i_rwsem.
158 */
159void
160ceph_end_io_direct(struct inode *inode)
161{
162	up_read(&inode->i_rwsem);
163}