ntfs3: Provide a splice-read wrapper

Provide a splice_read wrapper for NTFS3 to perform various checks before
allowing the operation to proceed.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Jens Axboe <axboe@kernel.dk>
cc: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
cc: ntfs3@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20230522135018.2742245-22-dhowells@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/ntfs3/file.c

@@ -744,6 +744,35 @@ static ssize_t ntfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 	return generic_file_read_iter(iocb, iter);
 }
 
+static ssize_t ntfs_file_splice_read(struct file *in, loff_t *ppos,
+				     struct pipe_inode_info *pipe,
+				     size_t len, unsigned int flags)
+{
+	struct inode *inode = in->f_mapping->host;
+	struct ntfs_inode *ni = ntfs_i(inode);
+
+	if (is_encrypted(ni)) {
+		ntfs_inode_warn(inode, "encrypted i/o not supported");
+		return -EOPNOTSUPP;
+	}
+
+#ifndef CONFIG_NTFS3_LZX_XPRESS
+	if (ni->ni_flags & NI_FLAG_COMPRESSED_MASK) {
+		ntfs_inode_warn(
+			inode,
+			"activate CONFIG_NTFS3_LZX_XPRESS to read external compressed files");
+		return -EOPNOTSUPP;
+	}
+#endif
+
+	if (is_dedup(ni)) {
+		ntfs_inode_warn(inode, "read deduplicated not supported");
+		return -EOPNOTSUPP;
+	}
+
+	return generic_file_splice_read(in, ppos, pipe, len, flags);
+}
+
 /*
  * ntfs_get_frame_pages
  *
@@ -1159,7 +1188,7 @@ const struct file_operations ntfs_file_operations = {
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= ntfs_compat_ioctl,
 #endif
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= ntfs_file_splice_read,
 	.mmap		= ntfs_file_mmap,
 	.open		= ntfs_file_open,
 	.fsync		= generic_file_fsync,