fs/dax.c

   1 /*
   2  * fs/dax.c - Direct Access filesystem code
   3  * Copyright (c) 2013-2014 Intel Corporation
   4  * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
   5  * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify it
   8  * under the terms and conditions of the GNU General Public License,
   9  * version 2, as published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14  * more details.
  15  */
  16
  17 #include <linux/atomic.h>
  18 #include <linux/blkdev.h>
  19 #include <linux/buffer_head.h>
  20 #include <linux/fs.h>
  21 #include <linux/genhd.h>
  22 #include <linux/mutex.h>
  23 #include <linux/uio.h>
  24
  25 static long dax_get_addr(struct buffer_head *bh, void **addr, unsigned blkbits)
  26 {
  27         unsigned long pfn;
  28         sector_t sector = bh->b_blocknr << (blkbits - 9);
  29         return bdev_direct_access(bh->b_bdev, sector, addr, &pfn, bh->b_size);
  30 }
  31
  32 static void dax_new_buf(void *addr, unsigned size, unsigned first, loff_t pos,
  33                         loff_t end)
  34 {
  35         loff_t final = end - pos + first; /* The final byte of the buffer */
  36
  37         if (first > 0)
  38                 memset(addr, 0, first);
  39         if (final < size)
  40                 memset(addr + final, 0, size - final);
  41 }
  42
  43 static bool buffer_written(struct buffer_head *bh)
  44 {
  45         return buffer_mapped(bh) && !buffer_unwritten(bh);
  46 }
  47
  48 /*
  49  * When ext4 encounters a hole, it returns without modifying the buffer_head
  50  * which means that we can't trust b_size.  To cope with this, we set b_state
  51  * to 0 before calling get_block and, if any bit is set, we know we can trust
  52  * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
  53  * and would save us time calling get_block repeatedly.
  54  */
  55 static bool buffer_size_valid(struct buffer_head *bh)
  56 {
  57         return bh->b_state != 0;
  58 }
  59
  60 static ssize_t dax_io(int rw, struct inode *inode, struct iov_iter *iter,
  61                         loff_t start, loff_t end, get_block_t get_block,
  62                         struct buffer_head *bh)
  63 {
  64         ssize_t retval = 0;
  65         loff_t pos = start;
  66         loff_t max = start;
  67         loff_t bh_max = start;
  68         void *addr;
  69         bool hole = false;
  70
  71         if (rw != WRITE)
  72                 end = min(end, i_size_read(inode));
  73
  74         while (pos < end) {
  75                 unsigned len;
  76                 if (pos == max) {
  77                         unsigned blkbits = inode->i_blkbits;
  78                         sector_t block = pos >> blkbits;
  79                         unsigned first = pos - (block << blkbits);
  80                         long size;
  81
  82                         if (pos == bh_max) {
  83                                 bh->b_size = PAGE_ALIGN(end - pos);
  84                                 bh->b_state = 0;
  85                                 retval = get_block(inode, block, bh,
  86                                                                 rw == WRITE);
  87                                 if (retval)
  88                                         break;
  89                                 if (!buffer_size_valid(bh))
  90                                         bh->b_size = 1 << blkbits;
  91                                 bh_max = pos - first + bh->b_size;
  92                         } else {
  93                                 unsigned done = bh->b_size -
  94                                                 (bh_max - (pos - first));
  95                                 bh->b_blocknr += done >> blkbits;
  96                                 bh->b_size -= done;
  97                         }
  98
  99                         hole = (rw != WRITE) && !buffer_written(bh);
 100                         if (hole) {
 101                                 addr = NULL;
 102                                 size = bh->b_size - first;
 103                         } else {
 104                                 retval = dax_get_addr(bh, &addr, blkbits);
 105                                 if (retval < 0)
 106                                         break;
 107                                 if (buffer_unwritten(bh) || buffer_new(bh))
 108                                         dax_new_buf(addr, retval, first, pos,
 109                                                                         end);
 110                                 addr += first;
 111                                 size = retval - first;
 112                         }
 113                         max = min(pos + size, end);
 114                 }
 115
 116                 if (rw == WRITE)
 117                         len = copy_from_iter(addr, max - pos, iter);
 118                 else if (!hole)
 119                         len = copy_to_iter(addr, max - pos, iter);
 120                 else
 121                         len = iov_iter_zero(max - pos, iter);
 122
 123                 if (!len)
 124                         break;
 125
 126                 pos += len;
 127                 addr += len;
 128         }
 129
 130         return (pos == start) ? retval : pos - start;
 131 }
 132
 133 /**
 134  * dax_do_io - Perform I/O to a DAX file
 135  * @rw: READ to read or WRITE to write
 136  * @iocb: The control block for this I/O
 137  * @inode: The file which the I/O is directed at
 138  * @iter: The addresses to do I/O from or to
 139  * @pos: The file offset where the I/O starts
 140  * @get_block: The filesystem method used to translate file offsets to blocks
 141  * @end_io: A filesystem callback for I/O completion
 142  * @flags: See below
 143  *
 144  * This function uses the same locking scheme as do_blockdev_direct_IO:
 145  * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
 146  * caller for writes.  For reads, we take and release the i_mutex ourselves.
 147  * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
 148  * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
 149  * is in progress.
 150  */
 151 ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode,
 152                         struct iov_iter *iter, loff_t pos,
 153                         get_block_t get_block, dio_iodone_t end_io, int flags)
 154 {
 155         struct buffer_head bh;
 156         ssize_t retval = -EINVAL;
 157         loff_t end = pos + iov_iter_count(iter);
 158
 159         memset(&bh, 0, sizeof(bh));
 160
 161         if ((flags & DIO_LOCKING) && (rw == READ)) {
 162                 struct address_space *mapping = inode->i_mapping;
 163                 mutex_lock(&inode->i_mutex);
 164                 retval = filemap_write_and_wait_range(mapping, pos, end - 1);
 165                 if (retval) {
 166                         mutex_unlock(&inode->i_mutex);
 167                         goto out;
 168                 }
 169         }
 170
 171         /* Protects against truncate */
 172         atomic_inc(&inode->i_dio_count);
 173
 174         retval = dax_io(rw, inode, iter, pos, end, get_block, &bh);
 175
 176         if ((flags & DIO_LOCKING) && (rw == READ))
 177                 mutex_unlock(&inode->i_mutex);
 178
 179         if ((retval > 0) && end_io)
 180                 end_io(iocb, pos, retval, bh.b_private);
 181
 182         inode_dio_done(inode);
 183  out:
 184         return retval;
 185 }
 186 EXPORT_SYMBOL_GPL(dax_do_io);