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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 : 0 : static void nfs_block_o_direct(struct nfs_inode *nfsi, struct inode *inode) 19 : : { 20 [ # # ]: 0 : if (test_bit(NFS_INO_ODIRECT, &nfsi->flags)) { 21 : 0 : clear_bit(NFS_INO_ODIRECT, &nfsi->flags); 22 : 0 : inode_dio_wait(inode); 23 : : } 24 : 0 : } 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 : 0 : nfs_start_io_read(struct inode *inode) 44 : : { 45 : 0 : struct nfs_inode *nfsi = NFS_I(inode); 46 : : /* Be an optimist! */ 47 : 0 : down_read(&inode->i_rwsem); 48 [ # # ]: 0 : if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0) 49 : : return; 50 : 0 : up_read(&inode->i_rwsem); 51 : : /* Slow path.... */ 52 : 0 : down_write(&inode->i_rwsem); 53 : 0 : nfs_block_o_direct(nfsi, inode); 54 : 0 : 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 : 0 : nfs_end_io_read(struct inode *inode) 66 : : { 67 : 0 : up_read(&inode->i_rwsem); 68 : 0 : } 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 : 0 : nfs_start_io_write(struct inode *inode) 79 : : { 80 : 0 : down_write(&inode->i_rwsem); 81 : 0 : nfs_block_o_direct(NFS_I(inode), inode); 82 : 0 : } 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 : 0 : nfs_end_io_write(struct inode *inode) 93 : : { 94 : 0 : up_write(&inode->i_rwsem); 95 : 0 : } 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 : 0 : nfs_start_io_direct(struct inode *inode) 124 : : { 125 : 0 : struct nfs_inode *nfsi = NFS_I(inode); 126 : : /* Be an optimist! */ 127 : 0 : down_read(&inode->i_rwsem); 128 [ # # ]: 0 : if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0) 129 : : return; 130 : 0 : up_read(&inode->i_rwsem); 131 : : /* Slow path.... */ 132 : 0 : down_write(&inode->i_rwsem); 133 : 0 : nfs_block_buffered(nfsi, inode); 134 : 0 : 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 : 0 : nfs_end_io_direct(struct inode *inode) 146 : : { 147 : 0 : up_read(&inode->i_rwsem); 148 : 0 : }