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From: Satya Tangirala <satyat@google.com>
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, Satya Tangirala <satyat@google.com>
Subject: [PATCH v3 7/7] fscrypt: update documentation for direct I/O support
Date: Fri, 17 Jul 2020 01:45:40 +0000
Message-ID: <20200717014540.71515-8-satyat@google.com> (raw)
In-Reply-To: <20200717014540.71515-1-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>
---
 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


  parent reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17  1:45 [PATCH v3 0/7] add support for direct I/O with fscrypt using blk-crypto Satya Tangirala
2020-07-17  1:45 ` [PATCH v3 1/7] fscrypt: Add functions for direct I/O support Satya Tangirala
2020-07-20 20:14   ` Eric Biggers
2020-07-17  1:45 ` [PATCH v3 2/7] direct-io: add support for fscrypt using blk-crypto Satya Tangirala
2020-07-17  1:45 ` [PATCH v3 3/7] iomap: support direct I/O with " Satya Tangirala
2020-07-20 19:29   ` Eric Biggers
2020-07-17  1:45 ` [PATCH v3 4/7] ext4: " Satya Tangirala
2020-07-17  1:45 ` [PATCH v3 5/7] f2fs: " Satya Tangirala
2020-07-17  1:45 ` [PATCH v3 6/7] fscrypt: document inline encryption support Satya Tangirala
2020-07-20 19:34   ` Eric Biggers
2020-07-17  1:45 ` Satya Tangirala [this message]
2020-07-20 19:40   ` [PATCH v3 7/7] fscrypt: update documentation for direct I/O support Eric Biggers

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