Update fscrypt documentation to reflect the addition of direct I/O support and document the necessary conditions for direct I/O on encrypted files. Signed-off-by: Satya Tangirala <satyat@xxxxxxxxxx> --- Documentation/filesystems/fscrypt.rst | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index f3d87a1a0a7f..95c76a5f0567 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -1049,8 +1049,10 @@ astute users may notice some differences in behavior: may be used to overwrite the source files but isn't guaranteed to be effective on all filesystems and storage devices. -- Direct I/O is not supported on encrypted files. Attempts to use - direct I/O on such files will fall back to buffered I/O. +- Direct I/O is supported on encrypted files only under some circumstances + (see `Direct I/O support`_ for details). When these circumstances are not + met, attempts to use direct I/O on such files will fall back to buffered + I/O. - The fallocate operations FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE are not supported on encrypted files and will @@ -1257,6 +1259,20 @@ without the key is subject to change in the future. It is only meant as a way to temporarily present valid filenames so that commands like ``rm -r`` work as expected on encrypted directories. +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, +any I/O must be aligned to the filesystem block size (*not* necessarily +the same as the block device's block size) - in particular, any userspace +buffer into which data is read/written from must also be aligned to the +filesystem 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. + Tests ===== -- 2.28.0.rc0.105.gf9edc3c819-goog
