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