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From: Satya Tangirala via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>
To: linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	 linux-f2fs-devel@lists.sourceforge.net,
	linux-ext4@vger.kernel.org
Cc: linux-xfs@vger.kernel.org, Jaegeuk Kim <jaegeuk@kernel.org>,
	Eric Biggers <ebiggers@google.com>,
	Satya Tangirala <satyat@google.com>
Subject: [f2fs-dev] [PATCH v6 7/7] fscrypt: update documentation for direct I/O support
Date: Fri, 24 Jul 2020 18:45:01 +0000
Message-ID: <20200724184501.1651378-8-satyat@google.com> (raw)
In-Reply-To: <20200724184501.1651378-1-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 | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index 423c5a0daf45..b9bbd6c612ff 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 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
@@ -1123,6 +1125,20 @@ 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,
+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.
+
 Encryption policy enforcement
 =============================
 
-- 
2.28.0.rc0.142.g3c755180ce-goog



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Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 18:44 [f2fs-dev] [PATCH v6 0/7] add support for direct I/O with fscrypt using blk-crypto Satya Tangirala via Linux-f2fs-devel
2020-07-24 18:44 ` [f2fs-dev] [PATCH v6 1/7] fscrypt: Add functions for direct I/O support Satya Tangirala via Linux-f2fs-devel
2020-07-25  0:14   ` Dave Chinner
2020-07-26  2:49     ` Eric Biggers
2020-07-27  0:58       ` Dave Chinner
2020-07-27  2:59         ` Eric Biggers
2020-07-27  4:47           ` Dave Chinner
2020-07-24 18:44 ` [f2fs-dev] [PATCH v6 2/7] direct-io: add support for fscrypt using blk-crypto Satya Tangirala via Linux-f2fs-devel
2020-07-24 18:44 ` [f2fs-dev] [PATCH v6 3/7] iomap: support direct I/O with " Satya Tangirala via Linux-f2fs-devel
2020-07-24 18:44 ` [f2fs-dev] [PATCH v6 4/7] ext4: " Satya Tangirala via Linux-f2fs-devel
2020-07-24 18:44 ` [f2fs-dev] [PATCH v6 5/7] f2fs: " Satya Tangirala via Linux-f2fs-devel
2020-07-24 18:45 ` [f2fs-dev] [PATCH v6 6/7] fscrypt: document inline encryption support Satya Tangirala via Linux-f2fs-devel
2020-07-27 16:43   ` Eric Biggers
2020-07-24 18:45 ` Satya Tangirala via Linux-f2fs-devel [this message]

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