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 int
  43 nfs_start_io_read(struct inode *inode)
  44 {
  45         struct nfs_inode *nfsi = NFS_I(inode);
  46         int err;
  47
  48         /* Be an optimist! */
  49         err = down_read_killable(&inode->i_rwsem);
  50         if (err)
  51                 return err;
  52         if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
  53                 return 0;
  54         up_read(&inode->i_rwsem);
  55
  56         /* Slow path.... */
  57         err = down_write_killable(&inode->i_rwsem);
  58         if (err)
  59                 return err;
  60         nfs_block_o_direct(nfsi, inode);
  61         downgrade_write(&inode->i_rwsem);
  62
  63         return 0;
  64 }
  65
  66 /**
  67  * nfs_end_io_read - declare that the buffered read operation is done
  68  * @inode: file inode
  69  *
  70  * Declare that a buffered read operation is done, and release the shared
  71  * lock on inode->i_rwsem.
  72  */
  73 void
  74 nfs_end_io_read(struct inode *inode)
  75 {
  76         up_read(&inode->i_rwsem);
  77 }
  78
  79 /**
  80  * nfs_start_io_write - declare the file is being used for buffered writes
  81  * @inode: file inode
  82  *
  83  * Declare that a buffered read operation is about to start, and ensure
  84  * that we block all direct I/O.
  85  */
  86 int
  87 nfs_start_io_write(struct inode *inode)
  88 {
  89         int err;
  90
  91         err = down_write_killable(&inode->i_rwsem);
  92         if (!err)
  93                 nfs_block_o_direct(NFS_I(inode), inode);
  94         return err;
  95 }
  96
  97 /**
  98  * nfs_end_io_write - declare that the buffered write operation is done
  99  * @inode: file inode
 100  *
 101  * Declare that a buffered write operation is done, and release the
 102  * lock on inode->i_rwsem.
 103  */
 104 void
 105 nfs_end_io_write(struct inode *inode)
 106 {
 107         up_write(&inode->i_rwsem);
 108 }
 109
 110 /* Call with exclusively locked inode->i_rwsem */
 111 static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
 112 {
 113         if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
 114                 set_bit(NFS_INO_ODIRECT, &nfsi->flags);
 115                 nfs_sync_mapping(inode->i_mapping);
 116         }
 117 }
 118
 119 /**
 120  * nfs_start_io_direct - declare the file is being used for direct i/o
 121  * @inode: file inode
 122  *
 123  * Declare that a direct I/O operation is about to start, and ensure
 124  * that we block all buffered I/O.
 125  * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
 126  * and holds a shared lock on inode->i_rwsem to ensure that the flag
 127  * cannot be changed.
 128  * In practice, this means that direct I/O operations are allowed to
 129  * execute in parallel, thanks to the shared lock, whereas buffered I/O
 130  * operations need to wait to grab an exclusive lock in order to clear
 131  * NFS_INO_ODIRECT.
 132  * Note that buffered writes and truncates both take a write lock on
 133  * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
 134  */
 135 int
 136 nfs_start_io_direct(struct inode *inode)
 137 {
 138         struct nfs_inode *nfsi = NFS_I(inode);
 139         int err;
 140
 141         /* Be an optimist! */
 142         err = down_read_killable(&inode->i_rwsem);
 143         if (err)
 144                 return err;
 145         if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
 146                 return 0;
 147         up_read(&inode->i_rwsem);
 148
 149         /* Slow path.... */
 150         err = down_write_killable(&inode->i_rwsem);
 151         if (err)
 152                 return err;
 153         nfs_block_buffered(nfsi, inode);
 154         downgrade_write(&inode->i_rwsem);
 155
 156         return 0;
 157 }
 158
 159 /**
 160  * nfs_end_io_direct - declare that the direct i/o operation is done
 161  * @inode: file inode
 162  *
 163  * Declare that a direct I/O operation is done, and release the shared
 164  * lock on inode->i_rwsem.
 165  */
 166 void
 167 nfs_end_io_direct(struct inode *inode)
 168 {
 169         up_read(&inode->i_rwsem);
 170 }