vfs,ext2: introduce IS_DAX(inode)

Use an inode flag to tag inodes which should avoid using the page cache.
Convert ext2 to use it instead of mapping_is_xip().  Prevent I/Os to files
tagged with the DAX flag from falling back to buffered I/O.

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 7 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index d9f5336552d7..1578c224285e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1723,9 +1723,11 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
                  * we've already read everything we wanted to, or if
                  * there was a short read because we hit EOF, go ahead
                  * and return.  Otherwise fallthrough to buffered io for
-                 * the rest of the read.
+                 * the rest of the read.  Buffered reads will not work for
+                 * DAX files, so don't bother trying.
                  */
-                if (retval < 0 || !iov_iter_count(iter) || *ppos >= size) {
+                if (retval < 0 || !iov_iter_count(iter) || *ppos >= size ||
+                    IS_DAX(inode)) {
                         file_accessed(file);
                         goto out;
                 }
@@ -2587,13 +2589,16 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
                 loff_t endbyte;
 
                 written = generic_file_direct_write(iocb, from, pos);
-                if (written < 0 || written == count)
-                        goto out;
-
                 /*
-                 * direct-io write to a hole: fall through to buffered I/O
-                 * for completing the rest of the request.
+                 * If the write stopped short of completing, fall back to
+                 * buffered writes.  Some filesystems do this for writes to
+                 * holes, for example.  For DAX files, a buffered write will
+                 * not succeed (even if it did, DAX does not handle dirty
+                 * page-cache pages correctly).
                  */
+                if (written < 0 || written == count || IS_DAX(inode))
+                        goto out;
+
                 pos += written;
                 count -= written;