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From: Satya Tangirala <satyat@google.com>
To: "Theodore Y . Ts'o" <tytso@mit.edu>,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	Eric Biggers <ebiggers@kernel.org>, Chao Yu <chao@kernel.org>,
	Jens Axboe <axboe@kernel.dk>,
	"Darrick J . Wong" <darrick.wong@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-fscrypt@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	linux-xfs@vger.kernel.org, linux-block@vger.kernel.org,
	linux-ext4@vger.kernel.org, Satya Tangirala <satyat@google.com>,
	Eric Biggers <ebiggers@google.com>
Subject: [PATCH v9 9/9] fscrypt: update documentation for direct I/O support
Date: Fri,  4 Jun 2021 21:09:08 +0000	[thread overview]
Message-ID: <20210604210908.2105870-10-satyat@google.com> (raw)
In-Reply-To: <20210604210908.2105870-1-satyat@google.com>

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@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 Documentation/filesystems/fscrypt.rst | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index 44b67ebd6e40..c0c1747fa2fb 100644
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -1047,8 +1047,10 @@ 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 encrypted
+  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
@@ -1121,6 +1123,21 @@ It is not currently possible to backup and restore encrypted files
 without the encryption key.  This would require special APIs which
 have not yet been implemented.
 
+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 starting position in the file and 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).
+
 Encryption policy enforcement
 =============================
 
-- 
2.32.0.rc1.229.g3e70b5a671-goog


  parent reply	other threads:[~2021-06-04 21:10 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-04 21:08 [PATCH v9 0/9] add support for direct I/O with fscrypt using blk-crypto Satya Tangirala
2021-06-04 21:09 ` [PATCH v9 1/9] block: blk-crypto-fallback: handle data unit split across multiple bvecs Satya Tangirala
2021-06-04 21:09 ` [PATCH v9 2/9] block: blk-crypto: relax alignment requirements for bvecs in bios Satya Tangirala
2021-06-04 21:09 ` [PATCH v9 3/9] fscrypt: add functions for direct I/O support Satya Tangirala
2021-07-23 20:42   ` Eric Biggers
2021-06-04 21:09 ` [PATCH v9 4/9] direct-io: add support for fscrypt using blk-crypto Satya Tangirala
2021-06-04 21:09 ` [PATCH v9 5/9] block: Make bio_iov_iter_get_pages() respect bio_required_sector_alignment() Satya Tangirala
2021-06-04 22:51   ` kernel test robot
2021-06-05  2:55   ` kernel test robot
2021-07-23 21:33   ` Eric Biggers
2021-07-24  7:19     ` Christoph Hellwig
2021-06-04 21:09 ` [PATCH v9 6/9] iomap: support direct I/O with fscrypt using blk-crypto Satya Tangirala
2021-07-22 19:04   ` Darrick J. Wong
2021-06-04 21:09 ` [PATCH v9 7/9] ext4: " Satya Tangirala
2021-06-04 21:09 ` [PATCH v9 8/9] f2fs: " Satya Tangirala
2021-06-04 21:09 ` Satya Tangirala [this message]
     [not found] ` <CAF2Aj3h-Gt3bOxH4wXB7aeQ3jVzR3TEqd3uLsh4T9Q=e6W6iqQ@mail.gmail.com>
2021-07-22 14:48   ` [PATCH v9 0/9] add support for " Eric Biggers
2021-08-04  8:26     ` Lee Jones

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