[PATCH v8 07/10] block: Add fops atomic write support

John Garry
2024-06-10T10:44:53Z

Support atomic writes by submitting a single BIO with the REQ_ATOMIC set.

It must be ensured that the atomic write adheres to its rules, like
naturally aligned offset, so call blkdev_dio_invalid() ->
blkdev_atomic_write_valid() [with renaming blkdev_dio_unaligned() to
blkdev_dio_invalid()] for this purpose. The BIO submission path currently
checks for atomic writes which are too large, so no need to check here.

In blkdev_direct_IO(), if the nr_pages exceeds BIO_MAX_VECS, then we cannot
produce a single BIO, so error in this case.

Finally set FMODE_CAN_ATOMIC_WRITE when the bdev can support atomic writes
and the associated file flag is for O_DIRECT.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
block/fops.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 376265935714..be36c9fbd500 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -34,9 +34,12 @@ static blk_opf_t dio_bio_write_op(struct kiocb *iocb)
return opf;
}

-static bool blkdev_dio_unaligned(struct block_device *bdev, loff_t pos,
- struct iov_iter *iter)
+static bool blkdev_dio_invalid(struct block_device *bdev, loff_t pos,
+ struct iov_iter *iter, bool is_atomic)
{
+ if (is_atomic && !generic_atomic_write_valid(iter, pos))
+ return true;
+
return pos & (bdev_logical_block_size(bdev) - 1) ||
!bdev_iter_is_aligned(bdev, iter);
}
@@ -72,6 +75,8 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
bio.bi_iter.bi_sector = pos >> SECTOR_SHIFT;
bio.bi_write_hint = file_inode(iocb->ki_filp)->i_write_hint;
bio.bi_ioprio = iocb->ki_ioprio;
+ if (iocb->ki_flags & IOCB_ATOMIC)
+ bio.bi_opf |= REQ_ATOMIC;

ret = bio_iov_iter_get_pages(&bio, iter);
if (unlikely(ret))
@@ -343,6 +348,9 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
task_io_account_write(bio->bi_iter.bi_size);
}

+ if (iocb->ki_flags & IOCB_ATOMIC)
+ bio->bi_opf |= REQ_ATOMIC;
+
if (iocb->ki_flags & IOCB_NOWAIT)
bio->bi_opf |= REQ_NOWAIT;

@@ -359,12 +367,13 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
{
struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
+ bool is_atomic = iocb->ki_flags & IOCB_ATOMIC;
unsigned int nr_pages;

if (!iov_iter_count(iter))
return 0;

- if (blkdev_dio_unaligned(bdev, iocb->ki_pos, iter))
+ if (blkdev_dio_invalid(bdev, iocb->ki_pos, iter, is_atomic))
return -EINVAL;

nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS + 1);
@@ -373,6 +382,8 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
return __blkdev_direct_IO_simple(iocb, iter, bdev,
nr_pages);
return __blkdev_direct_IO_async(iocb, iter, bdev, nr_pages);
+ } else if (is_atomic) {
+ return -EINVAL;
}
return __blkdev_direct_IO(iocb, iter, bdev, bio_max_segs(nr_pages));
}
@@ -612,6 +623,9 @@ static int blkdev_open(struct inode *inode, struct file *filp)
if (!bdev)
return -ENXIO;

+ if (bdev_can_atomic_write(bdev) && filp->f_flags & O_DIRECT)
+ filp->f_mode |= FMODE_CAN_ATOMIC_WRITE;
+
ret = bdev_open(bdev, mode, filp->private_data, NULL, filp);
if (ret)
blkdev_put_no_open(bdev);
--
2.31.1