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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 v8 8/8] fscrypt: update documentation for direct I/O support
Date: Thu, 21 Jan 2021 23:03:36 +0000	[thread overview]
Message-ID: <20210121230336.1373726-9-satyat@google.com> (raw)
In-Reply-To: <20210121230336.1373726-1-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
 =============================
 
-- 
2.30.0.280.ga3ce27912f-goog


  parent reply	other threads:[~2021-01-21 23:25 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-21 23:03 [PATCH v8 0/8] add support for direct I/O with fscrypt using blk-crypto Satya Tangirala
2021-01-21 23:03 ` [PATCH v8 1/8] block: blk-crypto-fallback: handle data unit split across multiple bvecs Satya Tangirala
2021-01-21 23:03 ` [PATCH v8 2/8] block: blk-crypto: relax alignment requirements for bvecs in bios Satya Tangirala
2021-01-21 23:03 ` [PATCH v8 3/8] fscrypt: add functions for direct I/O support Satya Tangirala
2021-01-21 23:03 ` [PATCH v8 4/8] direct-io: add support for fscrypt using blk-crypto Satya Tangirala
2021-01-21 23:03 ` [PATCH v8 5/8] iomap: support direct I/O with " Satya Tangirala
2021-01-21 23:03 ` [PATCH v8 6/8] ext4: " Satya Tangirala
2021-01-21 23:03 ` [PATCH v8 7/8] f2fs: " Satya Tangirala
2021-01-21 23:03 ` Satya Tangirala [this message]
     [not found] ` <CAF2Aj3jbEnnG1-bHARSt6xF12VKttg7Bt52gV=bEQUkaspDC9w@mail.gmail.com>
2021-05-25 18:10   ` [PATCH v8 0/8] add support for " Satya Tangirala
2021-05-26  8:02     ` Lee Jones
2021-06-09  2:45       ` Satya Tangirala
2021-06-30  9:47         ` Lee Jones

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