dax,ext2: replace XIP read and write with DAX I/O

Use the generic AIO infrastructure instead of custom read and write
methods.  In addition to giving us support for AIO, this adds the missing
locking between read() and truncate().

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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);