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| author |   Eric Biggers <ebiggers@google.com> | 2022-01-28 15:39:40 -0800 |
|---|---|---|
| committer | Eric Biggers <ebiggers@google.com> | 2022-02-08 11:02:18 -0800 |
| commit | cdaa1b1941f667814300799ddb74f3079517cd5a (patch) | |
| tree | c8a6c4ba935662cbbb33a3dac5c90c72f55957d1 /Documentation/filesystems/fscrypt.rst | |
| parent | f2fs: support direct I/O with fscrypt using blk-crypto (diff) | |
| download | linux-dev-cdaa1b1941f667814300799ddb74f3079517cd5a.tar.xz linux-dev-cdaa1b1941f667814300799ddb74f3079517cd5a.zip | |
fscrypt: update documentation for direct I/O support
Now that direct I/O is supported on encrypted files in some cases,
document what these cases are.
Link: https://lore.kernel.org/r/20220128233940.79464-6-ebiggers@kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'Documentation/filesystems/fscrypt.rst')
| -rw-r--r-- | Documentation/filesystems/fscrypt.rst | 25 |
1 files changed, 23 insertions, 2 deletions
diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 4d5d50dca65c..6ccd5efb25b7 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -1047,8 +1047,8 @@ 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. For details, see `Direct I/O support`_. - The fallocate operations FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE are not supported on encrypted files and will @@ -1179,6 +1179,27 @@ Inline encryption doesn't affect the ciphertext or other aspects of the on-disk format, so users may freely switch back and forth between using "inlinecrypt" and not using "inlinecrypt". +Direct I/O support +================== + +For direct I/O on an encrypted file to work, the following conditions +must be met (in addition to the conditions for direct I/O on an +unencrypted file): + +* The file must be using inline encryption. Usually this means that + the filesystem must be mounted with ``-o inlinecrypt`` and inline + encryption hardware must be present. However, a software fallback + is also available. For details, see `Inline encryption support`_. + +* The I/O request must be fully aligned to the filesystem block size. + This means that the file position the I/O is targeting, the lengths + of all I/O segments, and the memory addresses of all I/O buffers + must be multiples of this value. Note that the filesystem block + size may be greater than the logical block size of the block device. + +If either of the above conditions is not met, then direct I/O on the +encrypted file will fall back to buffered I/O. + Implementation details ====================== |