Re: [PATCH v7 8/8] fscrypt: update documentation for direct I/O support

[Eric Biggers]

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