[PATCH v4 3/7] iomap: support direct I/O with fscrypt using blk-crypto

[Satya Tangirala <satyat@google.com>]

From: Eric Biggers <ebiggers@google.com>

Wire up iomap direct I/O with the fscrypt additions for direct I/O.
This allows ext4 to support direct I/O on encrypted files when inline
encryption is enabled.

This change consists of two parts:

- Set a bio_crypt_ctx on bios for encrypted files, so that the file
  contents get encrypted (or decrypted).

- Ensure that encryption data unit numbers (DUNs) are contiguous within
  each bio.  Use the new function fscrypt_limit_io_pages() for this,
  since the iomap code works directly with logical ranges and thus
  doesn't have a chance to call fscrypt_mergeable_bio() on each page.

Note that fscrypt_limit_io_pages() is normally a no-op, as normally the
DUNs simply increment along with the logical blocks.  But it's needed to
handle an edge case in one of the fscrypt IV generation methods.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Co-developed-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
---
 fs/iomap/direct-io.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index ec7b78e6feca..12064daa3e3d 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -6,6 +6,7 @@
 #include <linux/module.h>
 #include <linux/compiler.h>
 #include <linux/fs.h>
+#include <linux/fscrypt.h>
 #include <linux/iomap.h>
 #include <linux/backing-dev.h>
 #include <linux/uio.h>
@@ -183,11 +184,16 @@ static void
 iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
 		unsigned len)
 {
+	struct inode *inode = file_inode(dio->iocb->ki_filp);
 	struct page *page = ZERO_PAGE(0);
 	int flags = REQ_SYNC | REQ_IDLE;
 	struct bio *bio;
 
 	bio = bio_alloc(GFP_KERNEL, 1);
+
+	/* encrypted direct I/O is guaranteed to be fs-block aligned */
+	WARN_ON_ONCE(fscrypt_needs_contents_encryption(inode));
+
 	bio_set_dev(bio, iomap->bdev);
 	bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
 	bio->bi_private = dio;
@@ -253,6 +259,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 		ret = nr_pages;
 		goto out;
 	}
+	nr_pages = fscrypt_limit_io_pages(inode, pos, nr_pages);
 
 	if (need_zeroout) {
 		/* zero out from the start of the block to the write offset */
@@ -270,6 +277,8 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 		}
 
 		bio = bio_alloc(GFP_KERNEL, nr_pages);
+		fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
+					  GFP_KERNEL);
 		bio_set_dev(bio, iomap->bdev);
 		bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
 		bio->bi_write_hint = dio->iocb->ki_hint;
@@ -306,9 +315,10 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 		dio->size += n;
 		copied += n;
 
-		nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
 		iomap_dio_submit_bio(dio, iomap, bio, pos);
 		pos += n;
+		nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
+		nr_pages = fscrypt_limit_io_pages(inode, pos, nr_pages);
 	} while (nr_pages);
 
 	/*
-- 
2.28.0.rc0.105.gf9edc3c819-goog