Btrfs: Add O_DIRECT read and write (writes == buffered + cache flush)

This adds basic O_DIRECT read and write support.  In the write case, we
just do a normal buffered write followed by a cache flush.  O_DIRECT +
O_SYNC are required to trigger metadata syncs.

In the read case, there is a basic btrfs_get_block call for use by
the generic O_DIRECT code.  This does honor multi-volume mapping rules
but it skips all checksumming.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 48f1d1b96450..32e778fb014e 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2265,6 +2265,70 @@ out:
         return em;
 }
 
+static int btrfs_get_block(struct inode *inode, sector_t iblock,
+                        struct buffer_head *bh_result, int create)
+{
+        struct extent_map *em;
+        u64 start = (u64)iblock << inode->i_blkbits;
+        struct btrfs_multi_bio *multi = NULL;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        u64 len;
+        u64 logical;
+        u64 map_length;
+        int ret = 0;
+
+        em = btrfs_get_extent(inode, NULL, 0, start, bh_result->b_size, 0);
+
+        if (!em || IS_ERR(em))
+                goto out;
+
+        if (em->start > start || em->start + em->len <= start)
+            goto out;
+
+        if (em->block_start == EXTENT_MAP_INLINE) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        if (em->block_start == EXTENT_MAP_HOLE ||
+            em->block_start == EXTENT_MAP_DELALLOC) {
+                goto out;
+        }
+
+        len = em->start + em->len - start;
+        len = min_t(u64, len, INT_LIMIT(typeof(bh_result->b_size)));
+
+        logical = start - em->start;
+        logical = em->block_start + logical;
+
+        map_length = len;
+        ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
+                              logical, &map_length, &multi, 0);
+        BUG_ON(ret);
+        bh_result->b_blocknr = multi->stripes[0].physical >> inode->i_blkbits;
+        bh_result->b_size = min(map_length, len);
+        bh_result->b_bdev = multi->stripes[0].dev->bdev;
+        set_buffer_mapped(bh_result);
+        kfree(multi);
+out:
+        free_extent_map(em);
+        return ret;
+}
+
+static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
+                        const struct iovec *iov, loff_t offset,
+                        unsigned long nr_segs)
+{
+        struct file *file = iocb->ki_filp;
+        struct inode *inode = file->f_mapping->host;
+
+        if (rw == WRITE)
+                return -EINVAL;
+
+        return blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
+                                  offset, nr_segs, btrfs_get_block, NULL);
+}
+
 static sector_t btrfs_bmap(struct address_space *mapping, sector_t iblock)
 {
         return extent_bmap(mapping, iblock, btrfs_get_extent);
@@ -3136,6 +3200,7 @@ out_fail:
         btrfs_throttle(root);
         return err;
 }
+
 static int btrfs_permission(struct inode *inode, int mask,
                             struct nameidata *nd)
 {
@@ -3193,6 +3258,7 @@ static struct address_space_operations btrfs_aops = {
         .readpages      = btrfs_readpages,
         .sync_page      = block_sync_page,
         .bmap           = btrfs_bmap,
+        .direct_IO      = btrfs_direct_IO,
         .invalidatepage = btrfs_invalidatepage,
         .releasepage    = btrfs_releasepage,
         .set_page_dirty = __set_page_dirty_nobuffers,