[PATCH v4 07/11] block: Add fops atomic write support

John Garry
2024-02-19T13:02:43Z

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.

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 | 31 ++++++++++++++++++++++++++++---
1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 28382b4d097a..563189c2fc5a 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -34,13 +34,27 @@ 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_atomic_write_valid(struct block_device *bdev, loff_t pos,
+ struct iov_iter *iter)
{
+ struct request_queue *q = bdev_get_queue(bdev);
+ unsigned int min_bytes = queue_atomic_write_unit_min_bytes(q);
+ unsigned int max_bytes = queue_atomic_write_unit_max_bytes(q);
+
+ return atomic_write_valid(pos, iter, min_bytes, max_bytes);
+}
+
+static bool blkdev_dio_invalid(struct block_device *bdev, loff_t pos,
+ struct iov_iter *iter, bool atomic_write)
+{
+ if (atomic_write && !blkdev_atomic_write_valid(bdev, pos, iter))
+ return true;
+
return pos & (bdev_logical_block_size(bdev) - 1) ||
!bdev_iter_is_aligned(bdev, iter);
}

+
#define DIO_INLINE_BIO_VECS 4

static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
@@ -71,6 +85,8 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
}
bio.bi_iter.bi_sector = pos >> SECTOR_SHIFT;
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))
@@ -341,6 +357,9 @@ 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;

@@ -357,13 +376,14 @@ 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 atomic_write = iocb->ki_flags & IOCB_ATOMIC;
loff_t pos = iocb->ki_pos;
unsigned int nr_pages;

if (!iov_iter_count(iter))
return 0;

- if (blkdev_dio_unaligned(bdev, pos, iter))
+ if (blkdev_dio_invalid(bdev, pos, iter, atomic_write))
return -EINVAL;

nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS + 1);
@@ -371,6 +391,8 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
if (is_sync_kiocb(iocb))
return __blkdev_direct_IO_simple(iocb, iter, nr_pages);
return __blkdev_direct_IO_async(iocb, iter, nr_pages);
+ } else if (atomic_write) {
+ return -EINVAL;
}
return __blkdev_direct_IO(iocb, iter, bio_max_segs(nr_pages));
}
@@ -616,6 +638,9 @@ static int blkdev_open(struct inode *inode, struct file *filp)
if (bdev_nowait(handle->bdev))
filp->f_mode |= FMODE_NOWAIT;

+ if (bdev_can_atomic_write(handle->bdev) && filp->f_flags & O_DIRECT)
+ filp->f_mode |= FMODE_CAN_ATOMIC_WRITE;
+
filp->f_mapping = handle->bdev->bd_inode->i_mapping;
filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
filp->private_data = handle;
--
2.31.1