[PATCH 02/10] btrfs: basic dax read

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/btrfs/Makefile |  1 +
 fs/btrfs/ctree.h  |  5 ++++
 fs/btrfs/dax.c    | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/file.c   | 13 ++++++++++-
 4 files changed, 86 insertions(+), 1 deletion(-)
 create mode 100644 fs/btrfs/dax.c

diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index ca693dd554e9..1fa77b875ae9 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -12,6 +12,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
 	   reada.o backref.o ulist.o qgroup.o send.o dev-replace.o raid56.o \
 	   uuid-tree.o props.o free-space-tree.o tree-checker.o
 
+btrfs-$(CONFIG_FS_DAX) += dax.o
 btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
 btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o
 btrfs-$(CONFIG_BTRFS_FS_REF_VERIFY) += ref-verify.o
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5cc470fa6a40..038d64ecebe5 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3685,6 +3685,11 @@ int btrfs_reada_wait(void *handle);
 void btrfs_reada_detach(void *handle);
 int btree_readahead_hook(struct extent_buffer *eb, int err);
 
+#ifdef CONFIG_FS_DAX
+/* dax.c */
+ssize_t btrfs_file_dax_read(struct kiocb *iocb, struct iov_iter *to);
+#endif /* CONFIG_FS_DAX */
+
 static inline int is_fstree(u64 rootid)
 {
 	if (rootid == BTRFS_FS_TREE_OBJECTID ||
diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c
new file mode 100644
index 000000000000..d614bf73bf8e
--- /dev/null
+++ b/fs/btrfs/dax.c
@@ -0,0 +1,68 @@
+#include <linux/dax.h>
+#include <linux/uio.h>
+#include "ctree.h"
+#include "btrfs_inode.h"
+
+static ssize_t em_dax_rw(struct inode *inode, struct extent_map *em, u64 pos,
+		u64 len, struct iov_iter *iter)
+{
+        struct dax_device *dax_dev = fs_dax_get_by_bdev(em->bdev);
+        ssize_t map_len;
+        pgoff_t blk_pg;
+        void *kaddr;
+        sector_t blk_start;
+        unsigned offset = pos & (PAGE_SIZE - 1);
+
+        len = min(len + offset, em->len - (pos - em->start));
+        len = ALIGN(len, PAGE_SIZE);
+        blk_start = (get_start_sect(em->bdev) << 9) + (em->block_start + (pos - em->start));
+        blk_pg = blk_start - offset;
+        map_len = dax_direct_access(dax_dev, PHYS_PFN(blk_pg), PHYS_PFN(len), &kaddr, NULL);
+        map_len = PFN_PHYS(map_len);
+        kaddr += offset;
+        map_len -= offset;
+        if (map_len > len)
+                map_len = len;
+        if (iov_iter_rw(iter) == WRITE)
+                return dax_copy_from_iter(dax_dev, blk_pg, kaddr, map_len, iter);
+        else
+                return dax_copy_to_iter(dax_dev, blk_pg, kaddr, map_len, iter);
+}
+
+ssize_t btrfs_file_dax_read(struct kiocb *iocb, struct iov_iter *to)
+{
+        size_t ret = 0, done = 0, count = iov_iter_count(to);
+        struct extent_map *em;
+        u64 pos = iocb->ki_pos;
+        u64 end = pos + count;
+        struct inode *inode = file_inode(iocb->ki_filp);
+
+        if (!count)
+                return 0;
+
+        end = i_size_read(inode) < end ? i_size_read(inode) : end;
+
+        while (pos < end) {
+                u64 len = end - pos;
+
+                em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, pos, len, 0);
+                if (IS_ERR(em)) {
+                        if (!ret)
+                                ret = PTR_ERR(em);
+                        goto out;
+                }
+
+                BUG_ON(em->flags & EXTENT_FLAG_FS_MAPPING);
+
+                ret = em_dax_rw(inode, em, pos, len, to);
+                if (ret < 0)
+                        goto out;
+                pos += ret;
+                done += ret;
+        }
+
+out:
+        iocb->ki_pos += done;
+        return done ? done : ret;
+}
+
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 58e93bce3036..ef6ed93f44d1 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3308,9 +3308,20 @@ static int btrfs_file_open(struct inode *inode, struct file *filp)
 	return generic_file_open(inode, filp);
 }
 
+static ssize_t btrfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+#ifdef CONFIG_FS_DAX
+	if (IS_DAX(inode))
+		return btrfs_file_dax_read(iocb, to);
+#endif
+	return generic_file_read_iter(iocb, to);
+}
+
 const struct file_operations btrfs_file_operations = {
 	.llseek		= btrfs_file_llseek,
-	.read_iter      = generic_file_read_iter,
+	.read_iter      = btrfs_file_read_iter,
 	.splice_read	= generic_file_splice_read,
 	.write_iter	= btrfs_file_write_iter,
 	.mmap		= btrfs_file_mmap,
-- 
2.16.4