On Wed 02-08-17 13:11:52, Mimi Zohar wrote:

On Wed, 2017-08-02 at 10:01 +0200, Jan Kara wrote:

quoted

On Tue 01-08-17 16:24:30, Mimi Zohar wrote:

quoted

From: Christoph Hellwig <hch@lst.de>

Add a new ->integrity_read file operation to read data for integrity
hash collection.  This is defined to be equivalent to ->read_iter,
except that it will be called with the i_rwsem held exclusively.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Matthew Garrett <redacted>
Cc: Jan Kara <jack@suse.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Chao Yu <redacted>
Cc: Steven Whitehouse <redacted>
Cc: Bob Peterson <redacted>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Dave Kleikamp <shaggy@kernel.org>
Cc: Ryusuke Konishi <redacted>
Cc: Mark Fasheh <redacted>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: "Darrick J. Wong" <redacted>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Mason <clm@fb.com>
Signed-off-by: Mimi Zohar <redacted>

...

quoted

+static ssize_t ext4_file_integrity_read_iter(struct kiocb *iocb,
+					     struct iov_iter *to)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	int o_direct = iocb->ki_flags & IOCB_DIRECT;
+
+	lockdep_assert_held(&inode->i_rwsem);
+	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
+		return -EIO;
+
+	if (!iov_iter_count(to))
+		return 0; /* skip atime */
+
+#ifdef CONFIG_FS_DAX
+	if (IS_DAX(inode))
+		return dax_iomap_rw(iocb, to, &ext4_iomap_ops);
+#endif
+	if (o_direct)
+		return -EINVAL;
+	return generic_file_read_iter(iocb, to);
+}

I have noticed this o_direct check - why is it only in ext4 and shouldn't
rather higher layers make sure IOCB_DIRECT iocbs cannot reach
.integrity_read() methods?

 
This failure happens when opening a file with O_DIRECT on a block
device that does not support dax (eg. loop). xfs makes it to here too,
but the call to generic_file_read_iter() fails properly with -EINVAL.?
(Only tested on those filesystems included that support dax (eg. ext2,
ext4, and xfs).)

Well, yes, ext2 and ext4 will silently fall back to buffered read (as do
pretty much all filesystems except for XFS). However I fail to see why IMA
should care (which is probably due to my lack of knowledge about IMA).
Is O_DIRECT somehow excepted from IMA? But then why it is not for DAX?

								Honza

-- 
Jan Kara [off-list ref]
SUSE Labs, CR
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