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, 9 insertions, 2 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 5fa450452f9b..5b9386452218 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -796,8 +796,6 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
                      PAGE_CACHE_SIZE / (sizeof(struct page *)));
         pinned[0] = NULL;
         pinned[1] = NULL;
-        if (file->f_flags & O_DIRECT)
-                return -EINVAL;
 
         pos = *ppos;
         start_pos = pos;
@@ -909,6 +907,15 @@ out_nolock:
                                       start_pos, num_written);
                 if (err < 0)
                         num_written = err;
+        } else if (num_written > 0 && (file->f_flags & O_DIRECT)) {
+                do_sync_mapping_range(inode->i_mapping, start_pos,
+                                      start_pos + num_written - 1,
+                                      SYNC_FILE_RANGE_WRITE |
+                                      SYNC_FILE_RANGE_WAIT_AFTER);
+
+                invalidate_mapping_pages(inode->i_mapping,
+                      start_pos >> PAGE_CACHE_SHIFT,
+                     (start_pos + num_written - 1) >> PAGE_CACHE_SHIFT);
         }
         current->backing_dev_info = NULL;
         return num_written ? num_written : err;