f2fs: support direct I/O with fscrypt using blk-crypto

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 checking fscrypt_dio_supported()
  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>
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Link: https://lore.kernel.org/r/20220128233940.79464-5-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8c417864c66a..020d47f97969 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -4044,6 +4044,13 @@ 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) {