[PATCH v6 01/13] iomap: inline iomap_dio_bio_opflags()

John Garry
2025-03-13T17:13:39Z

It is neater to build blk_opf_t fully in one place, so inline
iomap_dio_bio_opflags() in iomap_dio_bio_iter().

Also tidy up the logic in dealing with IOMAP_DIO_CALLER_COMP, in generally
separate the logic in dealing with flags associated with reads and writes.

Originally-from: Christoph Hellwig <hch@lst.de>
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
Should I change author?
fs/iomap/direct-io.c | 112 +++++++++++++++++++------------------------
1 file changed, 49 insertions(+), 63 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 5299f70428ef..8c1bec473586 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -312,27 +312,20 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
}

/*
- * Figure out the bio's operation flags from the dio request, the
- * mapping, and whether or not we want FUA. Note that we can end up
- * clearing the WRITE_THROUGH flag in the dio request.
+ * Use a FUA write if we need datasync semantics and this is a pure data I/O
+ * that doesn't require any metadata updates (including after I/O completion
+ * such as unwritten extent conversion) and the underlying device either
+ * doesn't have a volatile write cache or supports FUA.
+ * This allows us to avoid cache flushes on I/O completion.
*/
-static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
- const struct iomap *iomap, bool use_fua, bool atomic_hw)
+static inline bool iomap_dio_can_use_fua(const struct iomap *iomap,
+ struct iomap_dio *dio)
{
- blk_opf_t opflags = REQ_SYNC | REQ_IDLE;
-
- if (!(dio->flags & IOMAP_DIO_WRITE))
- return REQ_OP_READ;
-
- opflags |= REQ_OP_WRITE;
- if (use_fua)
- opflags |= REQ_FUA;
- else
- dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;
- if (atomic_hw)
- opflags |= REQ_ATOMIC;
-
- return opflags;
+ if (iomap->flags & (IOMAP_F_SHARED | IOMAP_F_DIRTY))
+ return false;
+ if (!(dio->flags & IOMAP_DIO_WRITE_THROUGH))
+ return false;
+ return !bdev_write_cache(iomap->bdev) || bdev_fua(iomap->bdev);
}

static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
@@ -340,52 +333,59 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
const struct iomap *iomap = &iter->iomap;
struct inode *inode = iter->inode;
unsigned int fs_block_size = i_blocksize(inode), pad;
- bool atomic_hw = iter->flags & IOMAP_ATOMIC_HW;
const loff_t length = iomap_length(iter);
loff_t pos = iter->pos;
- blk_opf_t bio_opf;
+ blk_opf_t bio_opf = REQ_SYNC | REQ_IDLE;
struct bio *bio;
bool need_zeroout = false;
- bool use_fua = false;
int nr_pages, ret = 0;
u64 copied = 0;
size_t orig_count;

- if (atomic_hw && length != iter->len)
- return -EINVAL;
-
if ((pos | length) & (bdev_logical_block_size(iomap->bdev) - 1) ||
!bdev_iter_is_aligned(iomap->bdev, dio->submit.iter))
return -EINVAL;

- if (iomap->type == IOMAP_UNWRITTEN) {
- dio->flags |= IOMAP_DIO_UNWRITTEN;
- need_zeroout = true;
- }
+ if (dio->flags & IOMAP_DIO_WRITE) {
+ bio_opf |= REQ_OP_WRITE;
+
+ if (iter->flags & IOMAP_ATOMIC_HW) {
+ if (length != iter->len)
+ return -EINVAL;
+ bio_opf |= REQ_ATOMIC;
+ }
+
+ if (iomap->type == IOMAP_UNWRITTEN) {
+ dio->flags |= IOMAP_DIO_UNWRITTEN;
+ need_zeroout = true;
+ }

- if (iomap->flags & IOMAP_F_SHARED)
- dio->flags |= IOMAP_DIO_COW;
+ if (iomap->flags & IOMAP_F_SHARED)
+ dio->flags |= IOMAP_DIO_COW;
+
+ if (iomap->flags & IOMAP_F_NEW) {
+ need_zeroout = true;
+ } else if (iomap->type == IOMAP_MAPPED) {
+ if (iomap_dio_can_use_fua(iomap, dio))
+ bio_opf |= REQ_FUA;
+ else
+ dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;
+ }

- if (iomap->flags & IOMAP_F_NEW) {
- need_zeroout = true;
- } else if (iomap->type == IOMAP_MAPPED) {
/*
- * Use a FUA write if we need datasync semantics, this is a pure
- * data IO that doesn't require any metadata updates (including
- * after IO completion such as unwritten extent conversion) and
- * the underlying device either supports FUA or doesn't have
- * a volatile write cache. This allows us to avoid cache flushes
- * on IO completion. If we can't use writethrough and need to
- * sync, disable in-task completions as dio completion will
- * need to call generic_write_sync() which will do a blocking
- * fsync / cache flush call.
+ * We can only do deferred completion for pure overwrites that
+ * don't require additional I/O at completion time.
+ *
+ * This rules out writes that need zeroing or extent conversion,
+ * extend the file size, or issue metadata I/O or cache flushes
+ * during completion processing.
*/
- if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
- (dio->flags & IOMAP_DIO_WRITE_THROUGH) &&
- (bdev_fua(iomap->bdev) || !bdev_write_cache(iomap->bdev)))
- use_fua = true;
- else if (dio->flags & IOMAP_DIO_NEED_SYNC)
+ if (need_zeroout || (pos >= i_size_read(inode)) ||
+ ((dio->flags & IOMAP_DIO_NEED_SYNC) &&
+ !(bio_opf & REQ_FUA)))
dio->flags &= ~IOMAP_DIO_CALLER_COMP;
+ } else {
+ bio_opf |= REQ_OP_READ;
}

/*
@@ -399,18 +399,6 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
if (!iov_iter_count(dio->submit.iter))
goto out;

- /*
- * We can only do deferred completion for pure overwrites that
- * don't require additional IO at completion. This rules out
- * writes that need zeroing or extent conversion, extend
- * the file size, or issue journal IO or cache flushes
- * during completion processing.
- */
- if (need_zeroout ||
- ((dio->flags & IOMAP_DIO_NEED_SYNC) && !use_fua) ||
- ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))
- dio->flags &= ~IOMAP_DIO_CALLER_COMP;
-
/*
* The rules for polled IO completions follow the guidelines as the
* ones we set for inline and deferred completions. If none of those
@@ -428,8 +416,6 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
goto out;
}

- bio_opf = iomap_dio_bio_opflags(dio, iomap, use_fua, atomic_hw);
-
nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
do {
size_t n;
@@ -461,7 +447,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
}

n = bio->bi_iter.bi_size;
- if (WARN_ON_ONCE(atomic_hw && n != length)) {
+ if (WARN_ON_ONCE((bio_opf & REQ_ATOMIC) && n != length)) {
/*
* This bio should have covered the complete length,
* which it doesn't, so error. We may need to zero out
--
2.31.1