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 */
  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 }