diff options
Diffstat (limited to 'fs/dax.c')
| -rw-r--r-- | fs/dax.c | 186 |
1 files changed, 186 insertions, 0 deletions
diff --git a/fs/dax.c b/fs/dax.c new file mode 100644 index 000000000000..1a2bdbfa3ea9 --- /dev/null +++ b/fs/dax.c @@ -0,0 +1,186 @@ +/* + * 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); |