fs/nfs/io.c

   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 }