[PATCH v3 0/7] iomap: incremental per-operation iter advance

[PATCH v3 0/7] iomap: incremental per-operation iter advance

[Brian Foster]

Hi all,

Here's v3 of the iomap incremental advance series. The most notable
changes in this version are some type fixups that lead to a tweak of
iomap_iter_advance() semantics and folding in a couple more advances in
unshare and zero range that were missed previously.

I also briefly considered a new iomap_iter_advance_full() or some such
helper for cases that have no use for the length variable, but I'm
deferring that because switching back to an s64 return for
iomap_iter_advance() would probably eliminate the need for that.

Christoph,

I dropped the R-b tag for patch 3 because the code changed enough that
it might be worth a second look, but otherwise I don't think the logic
has really changed. With the error passthru removed I think the advance
call from iomap_iter() can ultimately go away when remaining ops are
switched over. This should be able to eventually just check for an error
return, a (non-stale) failure to advance, or otherwise proceed or not
based on iter->len.

Thoughts, reviews, flames appreciated.

Brian

v3:
- Code style and comment fixups.
- Variable type fixups and rework of iomap_iter_advance() to return
  error/length separately.
- Advance the iter on unshare and zero range skip cases instead of
  returning length.
v2: https://lore.kernel.org/linux-fsdevel/20250122133434.535192-1-bfoster@redhat.com/
- More refactoring of iomap_iter[_advance]() logic. Lifted out iter
  continuation and stale logic and improved comments.
- Renamed some poorly named helpers and variables.
- Return remaining length for current iter from _iter_advance() and use
  appropriately.
v1: https://lore.kernel.org/linux-fsdevel/20241213143610.1002526-1-bfoster@redhat.com/
- Reworked and fixed a bunch of functional issues.
RFC: https://lore.kernel.org/linux-fsdevel/20241125140623.20633-1-bfoster@redhat.com/

Brian Foster (7):
  iomap: split out iomap check and reset logic from iter advance
  iomap: factor out iomap length helper
  iomap: refactor iter and advance continuation logic
  iomap: support incremental iomap_iter advances
  iomap: advance the iter directly on buffered writes
  iomap: advance the iter directly on unshare range
  iomap: advance the iter directly on zero range

 fs/iomap/buffered-io.c |  67 +++++++++++++--------------
 fs/iomap/iter.c        | 103 ++++++++++++++++++++++++++---------------
 include/linux/iomap.h  |  27 +++++++++--
 3 files changed, 120 insertions(+), 77 deletions(-)

-- 
2.47.1

[PATCH v3 1/7] iomap: split out iomap check and reset logic from iter advance

[Brian Foster]

In preparation for more granular iomap_iter advancing, break out
some of the logic associated with higher level iteration from
iomap_advance_iter(). Specifically, factor the iomap reset code into
a separate helper and lift the iomap.length check into the calling
code, similar to how ->iomap_end() calls are handled.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/iter.c | 49 ++++++++++++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 23 deletions(-)

diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c
index 3790918646af..731ea7267f27 100644
--- a/fs/iomap/iter.c
+++ b/fs/iomap/iter.c
@@ -7,6 +7,13 @@
 #include <linux/iomap.h>
 #include "trace.h"
 
+static inline void iomap_iter_reset_iomap(struct iomap_iter *iter)
+{
+	iter->processed = 0;
+	memset(&iter->iomap, 0, sizeof(iter->iomap));
+	memset(&iter->srcmap, 0, sizeof(iter->srcmap));
+}
+
 /*
  * Advance to the next range we need to map.
  *
@@ -14,32 +21,24 @@
  * processed - it was aborted because the extent the iomap spanned may have been
  * changed during the operation. In this case, the iteration behaviour is to
  * remap the unprocessed range of the iter, and that means we may need to remap
- * even when we've made no progress (i.e. iter->processed = 0). Hence the
- * "finished iterating" case needs to distinguish between
- * (processed = 0) meaning we are done and (processed = 0 && stale) meaning we
- * need to remap the entire remaining range.
+ * even when we've made no progress (i.e. count = 0). Hence the "finished
+ * iterating" case needs to distinguish between (count = 0) meaning we are done
+ * and (count = 0 && stale) meaning we need to remap the entire remaining range.
  */
-static inline int iomap_iter_advance(struct iomap_iter *iter)
+static inline int iomap_iter_advance(struct iomap_iter *iter, s64 count)
 {
 	bool stale = iter->iomap.flags & IOMAP_F_STALE;
 	int ret = 1;
 
-	/* handle the previous iteration (if any) */
-	if (iter->iomap.length) {
-		if (iter->processed < 0)
-			return iter->processed;
-		if (WARN_ON_ONCE(iter->processed > iomap_length(iter)))
-			return -EIO;
-		iter->pos += iter->processed;
-		iter->len -= iter->processed;
-		if (!iter->len || (!iter->processed && !stale))
-			ret = 0;
-	}
+	if (count < 0)
+		return count;
+	if (WARN_ON_ONCE(count > iomap_length(iter)))
+		return -EIO;
+	iter->pos += count;
+	iter->len -= count;
+	if (!iter->len || (!count && !stale))
+		ret = 0;
 
-	/* clear the per iteration state */
-	iter->processed = 0;
-	memset(&iter->iomap, 0, sizeof(iter->iomap));
-	memset(&iter->srcmap, 0, sizeof(iter->srcmap));
 	return ret;
 }
 
@@ -82,10 +81,14 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 			return ret;
 	}
 
+	/* advance and clear state from the previous iteration */
 	trace_iomap_iter(iter, ops, _RET_IP_);
-	ret = iomap_iter_advance(iter);
-	if (ret <= 0)
-		return ret;
+	if (iter->iomap.length) {
+		ret = iomap_iter_advance(iter, iter->processed);
+		iomap_iter_reset_iomap(iter);
+		if (ret <= 0)
+			return ret;
+	}
 
 	ret = ops->iomap_begin(iter->inode, iter->pos, iter->len, iter->flags,
 			       &iter->iomap, &iter->srcmap);
-- 
2.47.1

[PATCH v3 2/7] iomap: factor out iomap length helper

[Brian Foster]

In preparation to support more granular iomap iter advancing, factor
the pos/len values as parameters to length calculation.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/iomap.h | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 75bf54e76f3b..f5ca71ac2fa2 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -231,18 +231,33 @@ struct iomap_iter {
 int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops);
 
 /**
- * iomap_length - length of the current iomap iteration
+ * iomap_length_trim - trimmed length of the current iomap iteration
  * @iter: iteration structure
+ * @pos: File position to trim from.
+ * @len: Length of the mapping to trim to.
  *
- * Returns the length that the operation applies to for the current iteration.
+ * Returns a trimmed length that the operation applies to for the current
+ * iteration.
  */
-static inline u64 iomap_length(const struct iomap_iter *iter)
+static inline u64 iomap_length_trim(const struct iomap_iter *iter, loff_t pos,
+		u64 len)
 {
 	u64 end = iter->iomap.offset + iter->iomap.length;
 
 	if (iter->srcmap.type != IOMAP_HOLE)
 		end = min(end, iter->srcmap.offset + iter->srcmap.length);
-	return min(iter->len, end - iter->pos);
+	return min(len, end - pos);
+}
+
+/**
+ * iomap_length - length of the current iomap iteration
+ * @iter: iteration structure
+ *
+ * Returns the length that the operation applies to for the current iteration.
+ */
+static inline u64 iomap_length(const struct iomap_iter *iter)
+{
+	return iomap_length_trim(iter, iter->pos, iter->len);
 }
 
 /**
-- 
2.47.1

[PATCH v3 3/7] iomap: refactor iter and advance continuation logic

[Brian Foster]

In preparation for future changes and more generic use of
iomap_iter_advance(), lift the high level iter continuation logic
out of iomap_iter_advance() into the caller. Also add some comments
and rework iomap_iter() to jump straight to ->iomap_begin() on the
first iteration.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/iomap/iter.c       | 66 ++++++++++++++++++++++++-------------------
 include/linux/iomap.h |  1 +
 2 files changed, 38 insertions(+), 29 deletions(-)

diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c
index 731ea7267f27..0a13d50e9ffd 100644
--- a/fs/iomap/iter.c
+++ b/fs/iomap/iter.c
@@ -15,31 +15,17 @@ static inline void iomap_iter_reset_iomap(struct iomap_iter *iter)
 }
 
 /*
- * Advance to the next range we need to map.
- *
- * If the iomap is marked IOMAP_F_STALE, it means the existing map was not fully
- * processed - it was aborted because the extent the iomap spanned may have been
- * changed during the operation. In this case, the iteration behaviour is to
- * remap the unprocessed range of the iter, and that means we may need to remap
- * even when we've made no progress (i.e. count = 0). Hence the "finished
- * iterating" case needs to distinguish between (count = 0) meaning we are done
- * and (count = 0 && stale) meaning we need to remap the entire remaining range.
+ * Advance the current iterator position and return the length remaining for the
+ * current mapping.
  */
-static inline int iomap_iter_advance(struct iomap_iter *iter, s64 count)
+int iomap_iter_advance(struct iomap_iter *iter, u64 *count)
 {
-	bool stale = iter->iomap.flags & IOMAP_F_STALE;
-	int ret = 1;
-
-	if (count < 0)
-		return count;
-	if (WARN_ON_ONCE(count > iomap_length(iter)))
+	if (WARN_ON_ONCE(*count > iomap_length(iter)))
 		return -EIO;
-	iter->pos += count;
-	iter->len -= count;
-	if (!iter->len || (!count && !stale))
-		ret = 0;
-
-	return ret;
+	iter->pos += *count;
+	iter->len -= *count;
+	*count = iomap_length(iter);
+	return 0;
 }
 
 static inline void iomap_iter_done(struct iomap_iter *iter)
@@ -71,9 +57,16 @@ static inline void iomap_iter_done(struct iomap_iter *iter)
  */
 int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 {
+	bool stale = iter->iomap.flags & IOMAP_F_STALE;
+	s64 processed;
 	int ret;
 
-	if (iter->iomap.length && ops->iomap_end) {
+	trace_iomap_iter(iter, ops, _RET_IP_);
+
+	if (!iter->iomap.length)
+		goto begin;
+
+	if (ops->iomap_end) {
 		ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter),
 				iter->processed > 0 ? iter->processed : 0,
 				iter->flags, &iter->iomap);
@@ -81,15 +74,30 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 			return ret;
 	}
 
-	/* advance and clear state from the previous iteration */
-	trace_iomap_iter(iter, ops, _RET_IP_);
-	if (iter->iomap.length) {
-		ret = iomap_iter_advance(iter, iter->processed);
+	processed = iter->processed;
+	if (processed < 0) {
 		iomap_iter_reset_iomap(iter);
-		if (ret <= 0)
-			return ret;
+		return processed;
 	}
 
+	/*
+	 * Advance the iter and clear state from the previous iteration. The
+	 * remaining length of the previous iteration should be zero by this
+	 * point, so use iter->len to determine whether to continue onto the
+	 * next mapping. Explicitly terminate in the case where the current iter
+	 * has not advanced at all (i.e. no work was done for some reason)
+	 * unless the mapping has been marked stale and needs to be reprocessed.
+	 */
+	ret = iomap_iter_advance(iter, &processed);
+	if (!ret && iter->len > 0)
+		ret = 1;
+	if (ret > 0 && !iter->processed && !stale)
+		ret = 0;
+	iomap_iter_reset_iomap(iter);
+	if (ret <= 0)
+		return ret;
+
+begin:
 	ret = ops->iomap_begin(iter->inode, iter->pos, iter->len, iter->flags,
 			       &iter->iomap, &iter->srcmap);
 	if (ret < 0)
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index f5ca71ac2fa2..f304c602e5fe 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -229,6 +229,7 @@ struct iomap_iter {
 };
 
 int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops);
+int iomap_iter_advance(struct iomap_iter *iter, u64 *count);
 
 /**
  * iomap_length_trim - trimmed length of the current iomap iteration
-- 
2.47.1

Re: [PATCH v3 3/7] iomap: refactor iter and advance continuation logic

[Christoph Hellwig]

On Thu, Jan 30, 2025 at 12:09:44PM -0500, Brian Foster wrote:
> In preparation for future changes and more generic use of
> iomap_iter_advance(), lift the high level iter continuation logic
> out of iomap_iter_advance() into the caller. Also add some comments
> and rework iomap_iter() to jump straight to ->iomap_begin() on the
> first iteration.

It took me a bit to reoncile the commit log with the changes.

What this does is:

 1) factor out a iomap_iter_reset_iomap caller from iomap_iter_advance
 2) pass an explicit count to iomap_iter_advance instead of derіving
    it from iter->processed inside of iomap_iter_advance
 3) only call iomap_iter_advance condititional on iter->iomap.length,
    and thus skipping the code that is now in iomap_iter_reset_iomap
    when iter->iomap.length is 0.

All this looks fine, although I wonder why we didn't do 3) before and
if there is a risk of a regression for some weird corner case.

I hate nitpicking too much, but maybe split the three steps into
separate patches so that 3) is clearly documented and can be bisected
if problems arise?

Re: [PATCH v3 3/7] iomap: refactor iter and advance continuation logic

[Brian Foster]

On Fri, Jan 31, 2025 at 12:08:03AM -0800, Christoph Hellwig wrote:
> On Thu, Jan 30, 2025 at 12:09:44PM -0500, Brian Foster wrote:
> > In preparation for future changes and more generic use of
> > iomap_iter_advance(), lift the high level iter continuation logic
> > out of iomap_iter_advance() into the caller. Also add some comments
> > and rework iomap_iter() to jump straight to ->iomap_begin() on the
> > first iteration.
> 
> It took me a bit to reoncile the commit log with the changes.
> 
> What this does is:
> 
>  1) factor out a iomap_iter_reset_iomap caller from iomap_iter_advance
>  2) pass an explicit count to iomap_iter_advance instead of derіving
>     it from iter->processed inside of iomap_iter_advance
>  3) only call iomap_iter_advance condititional on iter->iomap.length,
>     and thus skipping the code that is now in iomap_iter_reset_iomap
>     when iter->iomap.length is 0.
> 
> All this looks fine, although I wonder why we didn't do 3) before and
> if there is a risk of a regression for some weird corner case.
> 
> I hate nitpicking too much, but maybe split the three steps into
> separate patches so that 3) is clearly documented and can be bisected
> if problems arise?
> 
> 

No problem. I originally had this split up, then combined some of it
because the changes seemed trivial, then I think it became a little too
convoluted again. I think I should be able to split this back up into
two or three incremental patches..

Brian

[PATCH v3 4/7] iomap: support incremental iomap_iter advances

[Brian Foster]

The current iomap_iter iteration model reads the mapping from the
filesystem, processes the subrange of the operation associated with
the current mapping, and returns the number of bytes processed back
to the iteration code. The latter advances the position and
remaining length of the iter in preparation for the next iteration.

At the _iter() handler level, this tends to produce a processing
loop where the local code pulls the current position and remaining
length out of the iter, iterates it locally based on file offset,
and then breaks out when the associated range has been fully
processed.

This works well enough for current handlers, but upcoming
enhancements require a bit more flexibility in certain situations.
Enhancements for zero range will lead to a situation where the
processing loop is no longer a pure ascending offset walk, but
rather dictated by pagecache state and folio lookup. Since folio
lookup and write preparation occur at different levels, it is more
difficult to manage position and length outside of the iter.

To provide more flexibility to certain iomap operations, introduce
support for incremental iomap_iter advances from within the
operation itself. This allows more granular advances for operations
that might not use the typical file offset based walk.

Note that the semantics for operations that use incremental advances
is slightly different than traditional operations. Operations that
advance the iter directly are expected to return success or failure
(i.e. 0 or negative error code) in iter.processed rather than the
number of bytes processed.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/iter.c       | 32 +++++++++++++++++++++++++-------
 include/linux/iomap.h |  3 +++
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c
index 0a13d50e9ffd..bb56996de09d 100644
--- a/fs/iomap/iter.c
+++ b/fs/iomap/iter.c
@@ -35,6 +35,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter)
 	WARN_ON_ONCE(iter->iomap.offset + iter->iomap.length <= iter->pos);
 	WARN_ON_ONCE(iter->iomap.flags & IOMAP_F_STALE);
 
+	iter->iter_start_pos = iter->pos;
+
 	trace_iomap_iter_dstmap(iter->inode, &iter->iomap);
 	if (iter->srcmap.type != IOMAP_HOLE)
 		trace_iomap_iter_srcmap(iter->inode, &iter->srcmap);
@@ -58,6 +60,8 @@ static inline void iomap_iter_done(struct iomap_iter *iter)
 int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 {
 	bool stale = iter->iomap.flags & IOMAP_F_STALE;
+	ssize_t advanced = iter->processed > 0 ? iter->processed : 0;
+	u64 olen = iter->len;
 	s64 processed;
 	int ret;
 
@@ -66,11 +70,22 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 	if (!iter->iomap.length)
 		goto begin;
 
+	/*
+	 * If iter.processed is zero, the op may still have advanced the iter
+	 * itself. Calculate the advanced and original length bytes based on how
+	 * far pos has advanced for ->iomap_end().
+	 */
+	if (!advanced) {
+		advanced = iter->pos - iter->iter_start_pos;
+		olen += advanced;
+	}
+
 	if (ops->iomap_end) {
-		ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter),
-				iter->processed > 0 ? iter->processed : 0,
-				iter->flags, &iter->iomap);
-		if (ret < 0 && !iter->processed)
+		ret = ops->iomap_end(iter->inode, iter->iter_start_pos,
+				iomap_length_trim(iter, iter->iter_start_pos,
+						  olen),
+				advanced, iter->flags, &iter->iomap);
+		if (ret < 0 && !advanced)
 			return ret;
 	}
 
@@ -81,8 +96,11 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 	}
 
 	/*
-	 * Advance the iter and clear state from the previous iteration. The
-	 * remaining length of the previous iteration should be zero by this
+	 * Advance the iter and clear state from the previous iteration. This
+	 * passes iter->processed because that reflects the bytes processed but
+	 * not yet advanced by the iter handler.
+	 *
+	 * The remaining length of the previous iteration should be zero by this
 	 * point, so use iter->len to determine whether to continue onto the
 	 * next mapping. Explicitly terminate in the case where the current iter
 	 * has not advanced at all (i.e. no work was done for some reason)
@@ -91,7 +109,7 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 	ret = iomap_iter_advance(iter, &processed);
 	if (!ret && iter->len > 0)
 		ret = 1;
-	if (ret > 0 && !iter->processed && !stale)
+	if (ret > 0 && !advanced && !stale)
 		ret = 0;
 	iomap_iter_reset_iomap(iter);
 	if (ret <= 0)
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index f304c602e5fe..0135a7f8dd83 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -211,6 +211,8 @@ struct iomap_ops {
  *	calls to iomap_iter().  Treat as read-only in the body.
  * @len: The remaining length of the file segment we're operating on.
  *	It is updated at the same time as @pos.
+ * @iter_start_pos: The original start pos for the current iomap. Used for
+ *	incremental iter advance.
  * @processed: The number of bytes processed by the body in the most recent
  *	iteration, or a negative errno. 0 causes the iteration to stop.
  * @flags: Zero or more of the iomap_begin flags above.
@@ -221,6 +223,7 @@ struct iomap_iter {
 	struct inode *inode;
 	loff_t pos;
 	u64 len;
+	loff_t iter_start_pos;
 	s64 processed;
 	unsigned flags;
 	struct iomap iomap;
-- 
2.47.1

[PATCH v3 5/7] iomap: advance the iter directly on buffered writes

[Brian Foster]

Modify the buffered write path to advance the iter directly. Replace
the local pos and length calculations with direct advances and loop
based on iter state instead.

Also remove the -EAGAIN return hack as it is no longer necessary now
that separate return channels exist for processing progress and error
returns. For example, the existing write handler must return either a
count of bytes written or error if the write is interrupted, but
presumably wants to return -EAGAIN directly in order to break the higher
level iomap_iter() loop.

Since the current iteration may have made some progress, it unwinds the
iter on the way out to return the error while ensuring that portion of
the write can be retried. If -EAGAIN occurs at any point beyond the
first iteration, iomap_file_buffered_write() will then observe progress
based on iter->pos to return a short write.

With incremental advances on the iomap_iter, iomap_write_iter() can
simply return the error. iomap_iter() completes whatever progress was
made based on iomap_iter position and still breaks out of the iter loop
based on the error code in iter.processed. The end result of the write
is similar in terms of being a short write if progress was made or error
return otherwise.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/buffered-io.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index d303e6c8900c..678c189faa58 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -909,8 +909,6 @@ static bool iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
 
 static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 {
-	loff_t length = iomap_length(iter);
-	loff_t pos = iter->pos;
 	ssize_t total_written = 0;
 	long status = 0;
 	struct address_space *mapping = iter->inode->i_mapping;
@@ -923,7 +921,8 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 		size_t offset;		/* Offset into folio */
 		size_t bytes;		/* Bytes to write to folio */
 		size_t copied;		/* Bytes copied from user */
-		size_t written;		/* Bytes have been written */
+		u64 written;		/* Bytes have been written */
+		loff_t pos = iter->pos;
 
 		bytes = iov_iter_count(i);
 retry:
@@ -934,8 +933,8 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 		if (unlikely(status))
 			break;
 
-		if (bytes > length)
-			bytes = length;
+		if (bytes > iomap_length(iter))
+			bytes = iomap_length(iter);
 
 		/*
 		 * Bring in the user page that we'll copy from _first_.
@@ -1006,17 +1005,12 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 				goto retry;
 			}
 		} else {
-			pos += written;
 			total_written += written;
-			length -= written;
+			iomap_iter_advance(iter, &written);
 		}
-	} while (iov_iter_count(i) && length);
+	} while (iov_iter_count(i) && iomap_length(iter));
 
-	if (status == -EAGAIN) {
-		iov_iter_revert(i, total_written);
-		return -EAGAIN;
-	}
-	return total_written ? total_written : status;
+	return total_written ? 0 : status;
 }
 
 ssize_t
-- 
2.47.1

[PATCH v3 6/7] iomap: advance the iter directly on unshare range

[Brian Foster]

Modify unshare range to advance the iter directly. Replace the local
pos and length calculations with direct advances and loop based on
iter state instead.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/iomap/buffered-io.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 678c189faa58..f953bf66beb1 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1267,20 +1267,19 @@ EXPORT_SYMBOL_GPL(iomap_write_delalloc_release);
 static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 {
 	struct iomap *iomap = &iter->iomap;
-	loff_t pos = iter->pos;
-	loff_t length = iomap_length(iter);
-	loff_t written = 0;
+	u64 bytes = iomap_length(iter);
+	int status;
 
 	if (!iomap_want_unshare_iter(iter))
-		return length;
+		return iomap_iter_advance(iter, &bytes);
 
 	do {
 		struct folio *folio;
-		int status;
 		size_t offset;
-		size_t bytes = min_t(u64, SIZE_MAX, length);
+		loff_t pos = iter->pos;
 		bool ret;
 
+		bytes = min_t(u64, SIZE_MAX, bytes);
 		status = iomap_write_begin(iter, pos, bytes, &folio);
 		if (unlikely(status))
 			return status;
@@ -1298,14 +1297,14 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 
 		cond_resched();
 
-		pos += bytes;
-		written += bytes;
-		length -= bytes;
-
 		balance_dirty_pages_ratelimited(iter->inode->i_mapping);
-	} while (length > 0);
 
-	return written;
+		status = iomap_iter_advance(iter, &bytes);
+		if (status)
+			break;
+	} while (bytes > 0);
+
+	return status;
 }
 
 int
-- 
2.47.1

Re: [PATCH v3 6/7] iomap: advance the iter directly on unshare range

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH v3 7/7] iomap: advance the iter directly on zero range

[Brian Foster]

Modify zero range to advance the iter directly. Replace the local pos
and length calculations with direct advances and loop based on iter
state instead.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/iomap/buffered-io.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f953bf66beb1..ec227b45f3aa 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1345,17 +1345,16 @@ static inline int iomap_zero_iter_flush_and_stale(struct iomap_iter *i)
 
 static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 {
-	loff_t pos = iter->pos;
-	loff_t length = iomap_length(iter);
-	loff_t written = 0;
+	u64 bytes = iomap_length(iter);
+	int status;
 
 	do {
 		struct folio *folio;
-		int status;
 		size_t offset;
-		size_t bytes = min_t(u64, SIZE_MAX, length);
+		loff_t pos = iter->pos;
 		bool ret;
 
+		bytes = min_t(u64, SIZE_MAX, bytes);
 		status = iomap_write_begin(iter, pos, bytes, &folio);
 		if (status)
 			return status;
@@ -1376,14 +1375,14 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 		if (WARN_ON_ONCE(!ret))
 			return -EIO;
 
-		pos += bytes;
-		length -= bytes;
-		written += bytes;
-	} while (length > 0);
+		status = iomap_iter_advance(iter, &bytes);
+		if (status)
+			break;
+	} while (bytes > 0);
 
 	if (did_zero)
 		*did_zero = true;
-	return written;
+	return status;
 }
 
 int
@@ -1436,11 +1435,14 @@ iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
 
 		if (srcmap->type == IOMAP_HOLE ||
 		    srcmap->type == IOMAP_UNWRITTEN) {
-			loff_t proc = iomap_length(&iter);
+			s64 proc;
 
 			if (range_dirty) {
 				range_dirty = false;
 				proc = iomap_zero_iter_flush_and_stale(&iter);
+			} else {
+				u64 length = iomap_length(&iter);
+				proc = iomap_iter_advance(&iter, &length);
 			}
 			iter.processed = proc;
 			continue;
-- 
2.47.1

Re: [PATCH v3 7/7] iomap: advance the iter directly on zero range

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>