On Tue, Nov 17, 2020 at 02:07:08PM +0000, Satya Tangirala wrote:

+Direct I/O support
+==================
+
+Direct I/O on encrypted files is supported through blk-crypto. In
+particular, this means the kernel must have CONFIG_BLK_INLINE_ENCRYPTION
+enabled, the filesystem must have had the 'inlinecrypt' mount option
+specified, and either hardware inline encryption must be present, or
+CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK must have been enabled. Further,
+the length of any I/O must be aligned to the filesystem block size
+(*not* necessarily the same as the block device's block size). If any of
+these conditions isn't met, attempts to do direct I/O on an encrypted file
+will fall back to buffered I/O. However, there aren't any additional
+requirements on user buffer alignment (apart from those already present
+when using direct I/O on unencrypted files).

Actually the position in the file the I/O is targeting must be fs-block aligned
too, not just the length of the I/O.

It's only the pointer to the user data buffer that no longer needs to be
fs-block aligned (this changed between v6 and v7).

- Eric