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+/*
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+ * fs/dax.c - Direct Access filesystem code
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+ * Copyright (c) 2013-2014 Intel Corporation
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+ * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
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+ * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
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+ *
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+ * This program is free software; you can redistribute it and/or modify it
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+ * under the terms and conditions of the GNU General Public License,
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+ * version 2, as published by the Free Software Foundation.
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+ *
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+ * This program is distributed in the hope it will be useful, but WITHOUT
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+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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+ * more details.
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+ */
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+
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+#include <linux/atomic.h>
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+#include <linux/blkdev.h>
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+#include <linux/buffer_head.h>
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+#include <linux/fs.h>
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+#include <linux/genhd.h>
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+#include <linux/mutex.h>
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+#include <linux/uio.h>
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+
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+static long dax_get_addr(struct buffer_head *bh, void **addr, unsigned blkbits)
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+{
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+ unsigned long pfn;
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+ sector_t sector = bh->b_blocknr << (blkbits - 9);
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+ return bdev_direct_access(bh->b_bdev, sector, addr, &pfn, bh->b_size);
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+}
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+
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+static void dax_new_buf(void *addr, unsigned size, unsigned first, loff_t pos,
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+ loff_t end)
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+{
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+ loff_t final = end - pos + first; /* The final byte of the buffer */
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+
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+ if (first > 0)
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+ memset(addr, 0, first);
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+ if (final < size)
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+ memset(addr + final, 0, size - final);
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+}
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+
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+static bool buffer_written(struct buffer_head *bh)
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+{
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+ return buffer_mapped(bh) && !buffer_unwritten(bh);
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+}
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+
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+/*
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+ * When ext4 encounters a hole, it returns without modifying the buffer_head
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+ * which means that we can't trust b_size. To cope with this, we set b_state
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+ * to 0 before calling get_block and, if any bit is set, we know we can trust
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+ * b_size. Unfortunate, really, since ext4 knows precisely how long a hole is
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+ * and would save us time calling get_block repeatedly.
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+ */
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+static bool buffer_size_valid(struct buffer_head *bh)
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+{
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+ return bh->b_state != 0;
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+}
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+
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+static ssize_t dax_io(int rw, struct inode *inode, struct iov_iter *iter,
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+ loff_t start, loff_t end, get_block_t get_block,
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+ struct buffer_head *bh)
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+{
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+ ssize_t retval = 0;
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+ loff_t pos = start;
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+ loff_t max = start;
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+ loff_t bh_max = start;
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+ void *addr;
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+ bool hole = false;
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+
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+ if (rw != WRITE)
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+ end = min(end, i_size_read(inode));
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+
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+ while (pos < end) {
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+ unsigned len;
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+ if (pos == max) {
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+ unsigned blkbits = inode->i_blkbits;
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+ sector_t block = pos >> blkbits;
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+ unsigned first = pos - (block << blkbits);
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+ long size;
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+
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+ if (pos == bh_max) {
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+ bh->b_size = PAGE_ALIGN(end - pos);
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+ bh->b_state = 0;
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+ retval = get_block(inode, block, bh,
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+ rw == WRITE);
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+ if (retval)
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+ break;
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+ if (!buffer_size_valid(bh))
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+ bh->b_size = 1 << blkbits;
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+ bh_max = pos - first + bh->b_size;
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+ } else {
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+ unsigned done = bh->b_size -
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+ (bh_max - (pos - first));
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+ bh->b_blocknr += done >> blkbits;
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+ bh->b_size -= done;
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+ }
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+
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+ hole = (rw != WRITE) && !buffer_written(bh);
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+ if (hole) {
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+ addr = NULL;
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+ size = bh->b_size - first;
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+ } else {
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+ retval = dax_get_addr(bh, &addr, blkbits);
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+ if (retval < 0)
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+ break;
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+ if (buffer_unwritten(bh) || buffer_new(bh))
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+ dax_new_buf(addr, retval, first, pos,
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+ end);
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+ addr += first;
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+ size = retval - first;
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+ }
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+ max = min(pos + size, end);
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+ }
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+
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+ if (rw == WRITE)
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+ len = copy_from_iter(addr, max - pos, iter);
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+ else if (!hole)
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+ len = copy_to_iter(addr, max - pos, iter);
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+ else
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+ len = iov_iter_zero(max - pos, iter);
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+
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+ if (!len)
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+ break;
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+
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+ pos += len;
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+ addr += len;
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+ }
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+
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+ return (pos == start) ? retval : pos - start;
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+}
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+
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+/**
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+ * dax_do_io - Perform I/O to a DAX file
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+ * @rw: READ to read or WRITE to write
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+ * @iocb: The control block for this I/O
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+ * @inode: The file which the I/O is directed at
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+ * @iter: The addresses to do I/O from or to
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+ * @pos: The file offset where the I/O starts
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+ * @get_block: The filesystem method used to translate file offsets to blocks
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+ * @end_io: A filesystem callback for I/O completion
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+ * @flags: See below
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+ *
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+ * This function uses the same locking scheme as do_blockdev_direct_IO:
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+ * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
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+ * caller for writes. For reads, we take and release the i_mutex ourselves.
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+ * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
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+ * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
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+ * is in progress.
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+ */
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+ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode,
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+ struct iov_iter *iter, loff_t pos,
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+ get_block_t get_block, dio_iodone_t end_io, int flags)
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+{
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+ struct buffer_head bh;
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+ ssize_t retval = -EINVAL;
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+ loff_t end = pos + iov_iter_count(iter);
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+
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+ memset(&bh, 0, sizeof(bh));
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+
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+ if ((flags & DIO_LOCKING) && (rw == READ)) {
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+ struct address_space *mapping = inode->i_mapping;
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+ mutex_lock(&inode->i_mutex);
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+ retval = filemap_write_and_wait_range(mapping, pos, end - 1);
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+ if (retval) {
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+ mutex_unlock(&inode->i_mutex);
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+ goto out;
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+ }
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+ }
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+
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+ /* Protects against truncate */
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+ atomic_inc(&inode->i_dio_count);
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+
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+ retval = dax_io(rw, inode, iter, pos, end, get_block, &bh);
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+
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+ if ((flags & DIO_LOCKING) && (rw == READ))
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+ mutex_unlock(&inode->i_mutex);
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+
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+ if ((retval > 0) && end_io)
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+ end_io(iocb, pos, retval, bh.b_private);
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+
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+ inode_dio_done(inode);
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+ out:
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+ return retval;
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+}
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+EXPORT_SYMBOL_GPL(dax_do_io);
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Matthew Wilcox