From: Dominique Martinet <asmadeus@codewreck.org>

After advancing into a folioq it makes more sense to point to the next
slot than at the end of the current slot.
This should not be needed for correctness, but this also happens to
"fix" the 9p bug with iterate_folioq() not copying properly.

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
---
 lib/iov_iter.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index f9193f952f49945297479483755d68a34c6d4ffe..65c05134ab934e1e0bf5d010fff22983bfe9c680 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1032,9 +1032,6 @@ static ssize_t iter_folioq_get_pages(struct iov_iter *iter,
 			maxpages--;
 		}
 
-		if (maxpages == 0 || extracted >= maxsize)
-			break;
-
 		if (iov_offset >= fsize) {
 			iov_offset = 0;
 			slot++;
@@ -1043,6 +1040,9 @@ static ssize_t iter_folioq_get_pages(struct iov_iter *iter,
 				slot = 0;
 			}
 		}
+
+		if (maxpages == 0 || extracted >= maxsize)
+			break;
 	}
 
 	iter->count = count;

-- 
2.50.1

Dominique Martinet via B4 Relay wrote:

> From: Dominique Martinet <asmadeus@codewreck.org>
> 
> After advancing into a folioq it makes more sense to point to the next
> slot than at the end of the current slot.
> This should not be needed for correctness, but this also happens to
> "fix" the 9p bug with iterate_folioq() not copying properly.
> 
> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

Acked-by: David Howells <dhowells@redhat.com>

Great! I can confirm this indeed fixes my reproducer, and the iov_iter
now looks sensible in gdb as far as I can judge.

Tested-by: Arnout Engelen <arnout@bzzt.net>

On Mon, Aug 11, 2025, at 09:39, Dominique Martinet via B4 Relay wrote:
> From: Dominique Martinet <asmadeus@codewreck.org>
> 
> After advancing into a folioq it makes more sense to point to the next
> slot than at the end of the current slot.
> This should not be needed for correctness, but this also happens to
> "fix" the 9p bug with iterate_folioq() not copying properly.
> 
> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
> ---
> lib/iov_iter.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index f9193f952f49945297479483755d68a34c6d4ffe..65c05134ab934e1e0bf5d010fff22983bfe9c680 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1032,9 +1032,6 @@ static ssize_t iter_folioq_get_pages(struct iov_iter *iter,
> maxpages--;
> }
>  
> - if (maxpages == 0 || extracted >= maxsize)
> - break;
> -
> if (iov_offset >= fsize) {
> iov_offset = 0;
> slot++;
> @@ -1043,6 +1040,9 @@ static ssize_t iter_folioq_get_pages(struct iov_iter *iter,
> slot = 0;
> }
> }
> +
> + if (maxpages == 0 || extracted >= maxsize)
> + break;
> }
>  
> iter->count = count;
> 
> -- 
> 2.50.1
> 
> 
> 

-- 
Arnout Engelen
Engelen Open Source
https://engelen.eu