This is a much simpler implementation of the DAX read/write path that makes
use of the iomap infrastructure. It does not try to mirror the direct I/O
calling conventions and thus doesn't have to deal with i_dio_count or the
end_io handler, but instead leaves locking and filesystem-specific I/O
completion to the caller.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
fs/dax.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/iomap.h | 2 +
2 files changed, 105 insertions(+)
diff --git a/fs/dax.c b/fs/dax.c
index 84343ce..57ad456 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -31,6 +31,8 @@
#include <linux/vmstat.h>
#include <linux/pfn_t.h>
#include <linux/sizes.h>
+#include <linux/iomap.h>
+#include "internal.h"
/*
* We use lowest available bit in exceptional entry for locking, other two
@@ -1241,3 +1243,104 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
return dax_zero_page_range(inode, from, length, get_block);
}
EXPORT_SYMBOL_GPL(dax_truncate_page);
+
+#ifdef CONFIG_FS_IOMAP
+static loff_t
+iomap_dax_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
+ struct iomap *iomap)
+{
+ struct iov_iter *iter = data;
+ loff_t end = pos + length, done = 0;
+ ssize_t ret = 0;
+
+ if (iov_iter_rw(iter) == READ) {
+ end = min(end, i_size_read(inode));
+ if (pos >= end)
+ return 0;
+
+ if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
+ return iov_iter_zero(min(length, end - pos), iter);
+ }
+
+ if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
+ return -EIO;
+
+ while (pos < end) {
+ unsigned offset = pos & (PAGE_SIZE - 1);
+ struct blk_dax_ctl dax = { 0 };
+ ssize_t map_len;
+
+ dax.sector = iomap->blkno +
+ (((pos & PAGE_MASK) - iomap->offset) >> 9);
+ dax.size = (length + offset + PAGE_SIZE - 1) & PAGE_MASK;
+ map_len = dax_map_atomic(iomap->bdev, &dax);
+ if (map_len < 0) {
+ ret = map_len;
+ break;
+ }
+
+ dax.addr += offset;
+ map_len -= offset;
+ if (map_len > end - pos)
+ map_len = end - pos;
+
+ if (iov_iter_rw(iter) == WRITE)
+ map_len = copy_from_iter_pmem(dax.addr, map_len, iter);
+ else
+ map_len = copy_to_iter(dax.addr, map_len, iter);
+ dax_unmap_atomic(iomap->bdev, &dax);
+ if (map_len <= 0) {
+ ret = map_len ? map_len : -EFAULT;
+ break;
+ }
+
+ pos += map_len;
+ length -= map_len;
+ done += map_len;
+ }
+
+ return done ? done : ret;
+}
+
+/**
+ * iomap_dax_rw - Perform I/O to a DAX file
+ * @iocb: The control block for this I/O
+ * @iter: The addresses to do I/O from or to
+ * @ops: iomap ops passed from the file system
+ *
+ * This funtions performs read and write operations to directly mapped
+ * persistent memory. The callers needs to take care of read/write exclusion
+ * and evicting any page cache pages in the region under I/O.
+ */
+ssize_t
+iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter,
+ struct iomap_ops *ops)
+{
+ struct inode *inode = iocb->ki_filp->f_mapping->host;
+ loff_t pos = iocb->ki_pos, ret = 0, done = 0;
+ size_t count = iov_iter_count(iter);
+ unsigned flags = 0;
+
+ if (!count)
+ return 0;
+
+ if (iov_iter_rw(iter) == WRITE)
+ flags |= IOMAP_WRITE;
+
+ do {
+ ret = iomap_apply(inode, pos, count, flags, ops, iter,
+ iomap_dax_actor);
+ if (ret <= 0)
+ break;
+ pos += ret;
+ done += ret;
+ } while ((count = iov_iter_count(iter)));
+
+ if (!done)
+ return ret;
+
+ iocb->ki_pos += done;
+ return done;
+}
+EXPORT_SYMBOL_GPL(iomap_dax_rw);
+#endif /* CONFIG_FS_IOMAP */
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 14d7067..3d5f785 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -65,6 +65,8 @@ struct iomap_ops {
ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
struct iomap_ops *ops);
+ssize_t iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter,
+ struct iomap_ops *ops);
int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
bool *did_zero, struct iomap_ops *ops);
int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
--
2.1.4
--
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