dax: provide an iomap based dax read/write path
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@lst.de>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
diff --git a/fs/dax.c b/fs/dax.c
index 84343ce..1f9f2d4 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 +1243,115 @@
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 function 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 address_space *mapping = iocb->ki_filp->f_mapping;
+ struct inode *inode = mapping->host;
+ loff_t pos = iocb->ki_pos, ret = 0, done = 0;
+ unsigned flags = 0;
+
+ if (iov_iter_rw(iter) == WRITE)
+ flags |= IOMAP_WRITE;
+
+ /*
+ * Yes, even DAX files can have page cache attached to them: A zeroed
+ * page is inserted into the pagecache when we have to serve a write
+ * fault on a hole. It should never be dirtied and can simply be
+ * dropped from the pagecache once we get real data for the page.
+ *
+ * XXX: This is racy against mmap, and there's nothing we can do about
+ * it. We'll eventually need to shift this down even further so that
+ * we can check if we allocated blocks over a hole first.
+ */
+ if (mapping->nrpages) {
+ ret = invalidate_inode_pages2_range(mapping,
+ pos >> PAGE_SHIFT,
+ (pos + iov_iter_count(iter) - 1) >> PAGE_SHIFT);
+ WARN_ON_ONCE(ret);
+ }
+
+ while (iov_iter_count(iter)) {
+ ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops,
+ iter, iomap_dax_actor);
+ if (ret <= 0)
+ break;
+ pos += ret;
+ done += ret;
+ }
+
+ iocb->ki_pos += done;
+ return done ? done : ret;
+}
+EXPORT_SYMBOL_GPL(iomap_dax_rw);
+#endif /* CONFIG_FS_IOMAP */