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 */ 18 static 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 */ 42 void 43 nfs_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 */ 64 void 65 nfs_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 */ 77 void 78 nfs_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 */ 91 void 92 nfs_end_io_write(struct inode *inode) 93 { 94 up_write(&inode->i_rwsem); 95 } 96 97 /* Call with exclusively locked inode->i_rwsem */ 98 static 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 */ 122 void 123 nfs_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 */ 144 void 145 nfs_end_io_direct(struct inode *inode) 146 { 147 up_read(&inode->i_rwsem); 148 } 149