LXR linux/fs/nfs/io.c

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