[PATCH v10 4/5] f2fs: support direct I/O with fscrypt using blk-crypto

Eric Biggers
2022-01-20T07:16:28Z

From: Eric Biggers <ebiggers@google.com>

Encrypted files traditionally haven't supported DIO, due to the need to
encrypt/decrypt the data. However, when the encryption is implemented
using inline encryption (blk-crypto) instead of the traditional
filesystem-layer encryption, it is straightforward to support DIO.

Therefore, make f2fs support DIO on files that are using inline
encryption. Since f2fs uses iomap for DIO, and fscrypt support was
already added to iomap DIO, this just requires two small changes:

- Let DIO proceed when supported, by using fscrypt_dio_unsupported()
instead of assuming that encrypted files never support DIO.

- In f2fs_iomap_begin(), use fscrypt_limit_io_blocks() to limit the
length of the mapping in the rare case where a DUN discontiguity
occurs in the middle of an extent. The iomap DIO implementation
requires this, since it assumes that it can submit a bio covering (up
to) the whole mapping, without checking fscrypt constraints itself.

Co-developed-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/f2fs/data.c | 7 +++++++
fs/f2fs/f2fs.h | 6 +++++-
2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 0a1d236212f85..90669c0d16c37 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -4057,6 +4057,13 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,

iomap->offset = blks_to_bytes(inode, map.m_lblk);

+ /*
+ * When inline encryption is enabled, sometimes I/O to an encrypted file
+ * has to be broken up to guarantee DUN contiguity. Handle this by
+ * limiting the length of the mapping returned.
+ */
+ map.m_len = fscrypt_limit_io_blocks(inode, map.m_lblk, map.m_len);
+
if (map.m_flags & (F2FS_MAP_MAPPED | F2FS_MAP_UNWRITTEN)) {
iomap->length = blks_to_bytes(inode, map.m_len);
if (map.m_flags & F2FS_MAP_MAPPED) {
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index eb22fa91c2b26..97f9e53969ece 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -4371,7 +4371,11 @@ static inline bool f2fs_force_buffered_io(struct inode *inode,
struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
int rw = iov_iter_rw(iter);

- if (f2fs_post_read_required(inode))
+ if (fscrypt_dio_unsupported(iocb, iter))
+ return true;
+ if (fsverity_active(inode))
+ return true;
+ if (f2fs_compressed_file(inode))
return true;

/* disallow direct IO if any of devices has unaligned blksize */
--
2.34.1