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 */ 17 static 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 */ 41 void 42 nfs_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 */ 63 void 64 nfs_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 */ 76 void 77 nfs_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 */ 90 void 91 nfs_end_io_write(struct inode *inode) 92 { 93 up_write(&inode->i_rwsem); 94 } 95 96 /* Call with exclusively locked inode->i_rwsem */ 97 static 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 */ 121 void 122 nfs_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 */ 143 void 144 nfs_end_io_direct(struct inode *inode) 145 { 146 up_read(&inode->i_rwsem); 147 } 148