1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * I/O and data path helper functionality. 4 * 5 * Borrowed from NFS Copyright (c) 2016 Trond Myklebust 6 */ 7 8 #include <linux/kernel.h> 9 #include <linux/netfs.h> 10 #include "internal.h" 11 12 /* 13 * inode_dio_wait_interruptible - wait for outstanding DIO requests to finish 14 * @inode: inode to wait for 15 * 16 * Waits for all pending direct I/O requests to finish so that we can 17 * proceed with a truncate or equivalent operation. 18 * 19 * Must be called under a lock that serializes taking new references 20 * to i_dio_count, usually by inode->i_mutex. 21 */ netfs_inode_dio_wait_interruptible(struct inode * inode)22 static int netfs_inode_dio_wait_interruptible(struct inode *inode) 23 { 24 if (inode_dio_finished(inode)) 25 return 0; 26 27 inode_dio_wait_interruptible(inode); 28 return !inode_dio_finished(inode) ? -ERESTARTSYS : 0; 29 } 30 31 /* Call with exclusively locked inode->i_rwsem */ netfs_block_o_direct(struct netfs_inode * ictx)32 static int netfs_block_o_direct(struct netfs_inode *ictx) 33 { 34 if (!test_bit(NETFS_ICTX_ODIRECT, &ictx->flags)) 35 return 0; 36 clear_bit(NETFS_ICTX_ODIRECT, &ictx->flags); 37 return netfs_inode_dio_wait_interruptible(&ictx->inode); 38 } 39 40 /** 41 * netfs_start_io_read - declare the file is being used for buffered reads 42 * @inode: file inode 43 * 44 * Declare that a buffered read operation is about to start, and ensure 45 * that we block all direct I/O. 46 * On exit, the function ensures that the NETFS_ICTX_ODIRECT flag is unset, 47 * and holds a shared lock on inode->i_rwsem to ensure that the flag 48 * cannot be changed. 49 * In practice, this means that buffered read operations are allowed to 50 * execute in parallel, thanks to the shared lock, whereas direct I/O 51 * operations need to wait to grab an exclusive lock in order to set 52 * NETFS_ICTX_ODIRECT. 53 * Note that buffered writes and truncates both take a write lock on 54 * inode->i_rwsem, meaning that those are serialised w.r.t. the reads. 55 */ netfs_start_io_read(struct inode * inode)56 int netfs_start_io_read(struct inode *inode) 57 __acquires(inode->i_rwsem) 58 { 59 struct netfs_inode *ictx = netfs_inode(inode); 60 61 /* Be an optimist! */ 62 if (down_read_interruptible(&inode->i_rwsem) < 0) 63 return -ERESTARTSYS; 64 if (test_bit(NETFS_ICTX_ODIRECT, &ictx->flags) == 0) 65 return 0; 66 up_read(&inode->i_rwsem); 67 68 /* Slow path.... */ 69 if (down_write_killable(&inode->i_rwsem) < 0) 70 return -ERESTARTSYS; 71 if (netfs_block_o_direct(ictx) < 0) { 72 up_write(&inode->i_rwsem); 73 return -ERESTARTSYS; 74 } 75 downgrade_write(&inode->i_rwsem); 76 return 0; 77 } 78 EXPORT_SYMBOL(netfs_start_io_read); 79 80 /** 81 * netfs_end_io_read - declare that the buffered read operation is done 82 * @inode: file inode 83 * 84 * Declare that a buffered read operation is done, and release the shared 85 * lock on inode->i_rwsem. 86 */ netfs_end_io_read(struct inode * inode)87 void netfs_end_io_read(struct inode *inode) 88 __releases(inode->i_rwsem) 89 { 90 up_read(&inode->i_rwsem); 91 } 92 EXPORT_SYMBOL(netfs_end_io_read); 93 94 /** 95 * netfs_start_io_write - declare the file is being used for buffered writes 96 * @inode: file inode 97 * 98 * Declare that a buffered read operation is about to start, and ensure 99 * that we block all direct I/O. 100 */ netfs_start_io_write(struct inode * inode)101 int netfs_start_io_write(struct inode *inode) 102 __acquires(inode->i_rwsem) 103 { 104 struct netfs_inode *ictx = netfs_inode(inode); 105 106 if (down_write_killable(&inode->i_rwsem) < 0) 107 return -ERESTARTSYS; 108 if (netfs_block_o_direct(ictx) < 0) { 109 up_write(&inode->i_rwsem); 110 return -ERESTARTSYS; 111 } 112 downgrade_write(&inode->i_rwsem); 113 return 0; 114 } 115 EXPORT_SYMBOL(netfs_start_io_write); 116 117 /** 118 * netfs_end_io_write - declare that the buffered write operation is done 119 * @inode: file inode 120 * 121 * Declare that a buffered write operation is done, and release the 122 * lock on inode->i_rwsem. 123 */ netfs_end_io_write(struct inode * inode)124 void netfs_end_io_write(struct inode *inode) 125 __releases(inode->i_rwsem) 126 { 127 up_read(&inode->i_rwsem); 128 } 129 EXPORT_SYMBOL(netfs_end_io_write); 130 131 /* Call with exclusively locked inode->i_rwsem */ netfs_block_buffered(struct inode * inode)132 static int netfs_block_buffered(struct inode *inode) 133 { 134 struct netfs_inode *ictx = netfs_inode(inode); 135 int ret; 136 137 if (!test_bit(NETFS_ICTX_ODIRECT, &ictx->flags)) { 138 set_bit(NETFS_ICTX_ODIRECT, &ictx->flags); 139 if (inode->i_mapping->nrpages != 0) { 140 unmap_mapping_range(inode->i_mapping, 0, 0, 0); 141 ret = filemap_fdatawait(inode->i_mapping); 142 if (ret < 0) { 143 clear_bit(NETFS_ICTX_ODIRECT, &ictx->flags); 144 return ret; 145 } 146 } 147 } 148 return 0; 149 } 150 151 /** 152 * netfs_start_io_direct - declare the file is being used for direct i/o 153 * @inode: file inode 154 * 155 * Declare that a direct I/O operation is about to start, and ensure 156 * that we block all buffered I/O. 157 * On exit, the function ensures that the NETFS_ICTX_ODIRECT flag is set, 158 * and holds a shared lock on inode->i_rwsem to ensure that the flag 159 * cannot be changed. 160 * In practice, this means that direct I/O operations are allowed to 161 * execute in parallel, thanks to the shared lock, whereas buffered I/O 162 * operations need to wait to grab an exclusive lock in order to clear 163 * NETFS_ICTX_ODIRECT. 164 * Note that buffered writes and truncates both take a write lock on 165 * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT. 166 */ netfs_start_io_direct(struct inode * inode)167 int netfs_start_io_direct(struct inode *inode) 168 __acquires(inode->i_rwsem) 169 { 170 struct netfs_inode *ictx = netfs_inode(inode); 171 int ret; 172 173 /* Be an optimist! */ 174 if (down_read_interruptible(&inode->i_rwsem) < 0) 175 return -ERESTARTSYS; 176 if (test_bit(NETFS_ICTX_ODIRECT, &ictx->flags) != 0) 177 return 0; 178 up_read(&inode->i_rwsem); 179 180 /* Slow path.... */ 181 if (down_write_killable(&inode->i_rwsem) < 0) 182 return -ERESTARTSYS; 183 ret = netfs_block_buffered(inode); 184 if (ret < 0) { 185 up_write(&inode->i_rwsem); 186 return ret; 187 } 188 downgrade_write(&inode->i_rwsem); 189 return 0; 190 } 191 EXPORT_SYMBOL(netfs_start_io_direct); 192 193 /** 194 * netfs_end_io_direct - declare that the direct i/o operation is done 195 * @inode: file inode 196 * 197 * Declare that a direct I/O operation is done, and release the shared 198 * lock on inode->i_rwsem. 199 */ netfs_end_io_direct(struct inode * inode)200 void netfs_end_io_direct(struct inode *inode) 201 __releases(inode->i_rwsem) 202 { 203 up_read(&inode->i_rwsem); 204 } 205 EXPORT_SYMBOL(netfs_end_io_direct); 206