Add test cases that test extract_iter_to_sg.

For each iterator type an iterator is loaded with a kernel
buffer. The iterator is then extracted to a scatterlist with
multiple calls to extract_iter_to_sg. The final scatterlist
is copied into a scratch buffer.

The test passes if the scratch buffer compares equal to the
original buffer.

The new tests demostrate bugs in extract_iter_to_sg
for kvec iterators that are fixed by the previous
commit.

Cc: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Christian A. Ehrhardt <lk@c--e.de>
---
 lib/tests/kunit_iov_iter.c | 152 +++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)

diff --git a/lib/tests/kunit_iov_iter.c b/lib/tests/kunit_iov_iter.c
index c42b9235f57a..159f61c9a30f 100644
--- a/lib/tests/kunit_iov_iter.c
+++ b/lib/tests/kunit_iov_iter.c
@@ -13,6 +13,7 @@
 #include <linux/uio.h>
 #include <linux/bvec.h>
 #include <linux/folio_queue.h>
+#include <linux/scatterlist.h>
 #include <linux/minmax.h>
 #include <kunit/test.h>
 
@@ -1014,6 +1015,153 @@ static void __init iov_kunit_extract_pages_xarray(struct kunit *test)
 	KUNIT_SUCCEED(test);
 }
 
+struct iov_kunit_iter_to_sg_data {
+	struct sg_table sgt;
+	u8 *buffer, *scratch;
+	struct page **pages;
+	size_t npages;
+};
+
+static void __init
+iov_kunit_iter_to_sg_init(struct kunit *test, size_t bufsize,
+			  struct iov_kunit_iter_to_sg_data *data)
+{
+	struct page **spages;
+	struct scatterlist *sg;
+	size_t i;
+
+	data->npages = bufsize / PAGE_SIZE;
+	sg = kunit_kmalloc_array(test, data->npages, sizeof(*sg), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, sg);
+	sg_init_table(sg, data->npages);
+	memset(&data->sgt, 0, sizeof(data->sgt));
+	data->sgt.orig_nents = data->npages;
+	data->sgt.sgl = sg;
+
+	data->buffer = iov_kunit_create_buffer(test, &data->pages,
+					       data->npages);
+	data->scratch = iov_kunit_create_buffer(test, &spages, data->npages);
+	for (i = 0; i < bufsize; ++i)
+		data->buffer[i] = pattern(i);
+	memset(data->scratch, 0, bufsize);
+}
+
+static void __init
+iov_kunit_iter_to_sg_check(struct kunit *test, struct iov_iter *iter,
+			   size_t bufsize,
+			   struct iov_kunit_iter_to_sg_data *data)
+{
+	size_t i;
+
+	i = extract_iter_to_sg(iter, bufsize, &data->sgt, 0, 0);
+	KUNIT_EXPECT_EQ(test, i, 0);
+	KUNIT_EXPECT_EQ(test, data->sgt.nents, 0);
+
+	i = extract_iter_to_sg(iter, bufsize, &data->sgt, 1, 0);
+	KUNIT_EXPECT_LE(test, i, bufsize);
+	KUNIT_EXPECT_EQ(test, data->sgt.nents, 1);
+
+	i += extract_iter_to_sg(iter, bufsize - i, &data->sgt,
+				data->npages - data->sgt.nents, 0);
+
+	KUNIT_EXPECT_EQ(test, i, bufsize);
+	KUNIT_EXPECT_LE(test, data->sgt.nents, data->npages);
+	sg_mark_end(&data->sgt.sgl[data->sgt.nents - 1]);
+
+
+	i = sg_copy_to_buffer(data->sgt.sgl, data->sgt.nents,
+			      data->scratch, bufsize);
+	KUNIT_EXPECT_EQ(test, i, bufsize);
+
+	for (i = 0; i < bufsize; ++i) {
+		KUNIT_EXPECT_EQ_MSG(test, data->buffer[i], data->scratch[i],
+				    "at i=%zx", i);
+		if (data->buffer[i] != data->scratch[i])
+			break;
+	}
+
+	KUNIT_EXPECT_EQ(test, i, bufsize);
+}
+
+static void __init iov_kunit_iter_to_sg_kvec(struct kunit *test)
+{
+	struct iov_kunit_iter_to_sg_data data;
+	struct iov_iter iter;
+	struct kvec kvec;
+	size_t bufsize;
+
+	bufsize = 0x100000;
+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
+
+	kvec.iov_base = data.buffer;
+	kvec.iov_len = bufsize;
+	iov_iter_kvec(&iter, READ, &kvec, 1, bufsize);
+
+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
+}
+
+static void __init iov_kunit_iter_to_sg_bvec(struct kunit *test)
+{
+	struct iov_kunit_iter_to_sg_data data;
+	struct page *p, *can_merge = NULL;
+	size_t i, k, bufsize;
+	struct bio_vec *bvec;
+	struct iov_iter iter;
+
+	bufsize = 0x100000;
+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
+
+	bvec = kunit_kmalloc_array(test, data.npages, sizeof(*bvec),
+				   GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, bvec);
+	k = 0;
+	for (i = 0; i < data.npages; ++i) {
+		p = data.pages[i];
+		if (p == can_merge)
+			bvec[k-1].bv_len += PAGE_SIZE;
+		else
+			bvec_set_page(&bvec[k++], p, PAGE_SIZE, 0);
+		can_merge = p + 1;
+	}
+	iov_iter_bvec(&iter, READ, bvec, k, bufsize);
+
+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
+}
+
+static void __init iov_kunit_iter_to_sg_folioq(struct kunit *test)
+{
+	struct iov_kunit_iter_to_sg_data data;
+	struct folio_queue *folioq;
+	struct iov_iter iter;
+	size_t bufsize;
+
+	bufsize = 0x100000;
+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
+
+	folioq = iov_kunit_create_folioq(test);
+	iov_kunit_load_folioq(test, &iter, READ, folioq, data.pages,
+			      data.npages);
+
+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
+}
+
+static void __init iov_kunit_iter_to_sg_xarray(struct kunit *test)
+{
+	struct iov_kunit_iter_to_sg_data data;
+	struct xarray *xarray;
+	struct iov_iter iter;
+	size_t bufsize;
+
+	bufsize = 0x100000;
+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
+
+	xarray = iov_kunit_create_xarray(test);
+	iov_kunit_load_xarray(test, &iter, READ, xarray, data.pages,
+			      data.npages);
+
+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
+}
+
 static struct kunit_case __refdata iov_kunit_cases[] = {
 	KUNIT_CASE(iov_kunit_copy_to_kvec),
 	KUNIT_CASE(iov_kunit_copy_from_kvec),
@@ -1027,6 +1175,10 @@ static struct kunit_case __refdata iov_kunit_cases[] = {
 	KUNIT_CASE(iov_kunit_extract_pages_bvec),
 	KUNIT_CASE(iov_kunit_extract_pages_folioq),
 	KUNIT_CASE(iov_kunit_extract_pages_xarray),
+	KUNIT_CASE(iov_kunit_iter_to_sg_kvec),
+	KUNIT_CASE(iov_kunit_iter_to_sg_bvec),
+	KUNIT_CASE(iov_kunit_iter_to_sg_folioq),
+	KUNIT_CASE(iov_kunit_iter_to_sg_xarray),
 	{}
 };
 
-- 
2.43.0

On 24 March 2026 20:34:53 GMT, "Christian A. Ehrhardt" <lk@c--e.de> wrote:
>Add test cases that test extract_iter_to_sg.
>
>For each iterator type an iterator is loaded with a kernel
>buffer. The iterator is then extracted to a scatterlist with
>multiple calls to extract_iter_to_sg. The final scatterlist
>is copied into a scratch buffer.
>
>The test passes if the scratch buffer compares equal to the
>original buffer.
>
>The new tests demostrate bugs in extract_iter_to_sg
>for kvec iterators that are fixed by the previous
>commit.

Nit: just a quick typo here: change demostrate to demonstrate.

>Cc: David Howells <dhowells@redhat.com>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Signed-off-by: Christian A. Ehrhardt <lk@c--e.de>
>---
> lib/tests/kunit_iov_iter.c | 152 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 152 insertions(+)
>
>diff --git a/lib/tests/kunit_iov_iter.c b/lib/tests/kunit_iov_iter.c
>index c42b9235f57a..159f61c9a30f 100644
>--- a/lib/tests/kunit_iov_iter.c
>+++ b/lib/tests/kunit_iov_iter.c
>@@ -13,6 +13,7 @@
> #include <linux/uio.h>
> #include <linux/bvec.h>
> #include <linux/folio_queue.h>
>+#include <linux/scatterlist.h>
> #include <linux/minmax.h>
> #include <kunit/test.h>
> 
>@@ -1014,6 +1015,153 @@ static void __init iov_kunit_extract_pages_xarray(struct kunit *test)
> 	KUNIT_SUCCEED(test);
> }
> 
>+struct iov_kunit_iter_to_sg_data {
>+	struct sg_table sgt;
>+	u8 *buffer, *scratch;
>+	struct page **pages;
>+	size_t npages;
>+};
>+
>+static void __init
>+iov_kunit_iter_to_sg_init(struct kunit *test, size_t bufsize,
>+			  struct iov_kunit_iter_to_sg_data *data)
>+{
>+	struct page **spages;
>+	struct scatterlist *sg;
>+	size_t i;
>+
>+	data->npages = bufsize / PAGE_SIZE;
>+	sg = kunit_kmalloc_array(test, data->npages, sizeof(*sg), GFP_KERNEL);
>+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, sg);
>+	sg_init_table(sg, data->npages);
>+	memset(&data->sgt, 0, sizeof(data->sgt));
>+	data->sgt.orig_nents = data->npages;
>+	data->sgt.sgl = sg;

Good code here

>+
>+	data->buffer = iov_kunit_create_buffer(test, &data->pages,
>+					       data->npages);
>+	data->scratch = iov_kunit_create_buffer(test, &spages, data->npages);
>+	for (i = 0; i < bufsize; ++i)
>+		data->buffer[i] = pattern(i);
>+	memset(data->scratch, 0, bufsize);
>+}
>+
>+static void __init
>+iov_kunit_iter_to_sg_check(struct kunit *test, struct iov_iter *iter,
>+			   size_t bufsize,
>+			   struct iov_kunit_iter_to_sg_data *data)
>+{
>+	size_t i;
>+
>+	i = extract_iter_to_sg(iter, bufsize, &data->sgt, 0, 0);
>+	KUNIT_EXPECT_EQ(test, i, 0);
>+	KUNIT_EXPECT_EQ(test, data->sgt.nents, 0);
>+
>+	i = extract_iter_to_sg(iter, bufsize, &data->sgt, 1, 0);
>+	KUNIT_EXPECT_LE(test, i, bufsize);
>+	KUNIT_EXPECT_EQ(test, data->sgt.nents, 1);
>+
>+	i += extract_iter_to_sg(iter, bufsize - i, &data->sgt,
>+				data->npages - data->sgt.nents, 0);
>+
>+	KUNIT_EXPECT_EQ(test, i, bufsize);
>+	KUNIT_EXPECT_LE(test, data->sgt.nents, data->npages);
>+	sg_mark_end(&data->sgt.sgl[data->sgt.nents - 1]);
>+
>+
>+	i = sg_copy_to_buffer(data->sgt.sgl, data->sgt.nents,
>+			      data->scratch, bufsize);
>+	KUNIT_EXPECT_EQ(test, i, bufsize);
>+
>+	for (i = 0; i < bufsize; ++i) {
>+		KUNIT_EXPECT_EQ_MSG(test, data->buffer[i], data->scratch[i],
>+				    "at i=%zx", i);
>+		if (data->buffer[i] != data->scratch[i])
>+			break;
>+	}

Nit: While KUNIT_EXPECT_EQ_MSG is great, checking byte-by-byte for a 1MB buffer (bufsize = 0x100000) inside a loop can be a bit slow in KUnit if failures occur and it tries to print thousands of messages before breaking. 
The if (...) break; handles the spew perfectly, but you could also just use a memcmp() first, and only drop into the loop to find the exact offset if the memcmp() fails.

    if (memcmp(data->buffer, data->scratch, bufsize)) {
        for (i = 0; i < bufsize; ++i) {
            KUNIT_EXPECT_EQ_MSG(test, data->buffer[i], data->scratch[i],
                        "at i=%zx", i);
            if (data->buffer[i] != data->scratch[i])
                break;
        }
    }

Could be good? (Completely optional!)

>+
>+	KUNIT_EXPECT_EQ(test, i, bufsize);
>+}
>+
>+static void __init iov_kunit_iter_to_sg_kvec(struct kunit *test)
>+{
>+	struct iov_kunit_iter_to_sg_data data;
>+	struct iov_iter iter;
>+	struct kvec kvec;
>+	size_t bufsize;
>+
>+	bufsize = 0x100000;
>+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
>+
>+	kvec.iov_base = data.buffer;
>+	kvec.iov_len = bufsize;
>+	iov_iter_kvec(&iter, READ, &kvec, 1, bufsize);
>+
>+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
>+}
>+
>+static void __init iov_kunit_iter_to_sg_bvec(struct kunit *test)
>+{
>+	struct iov_kunit_iter_to_sg_data data;
>+	struct page *p, *can_merge = NULL;
>+	size_t i, k, bufsize;
>+	struct bio_vec *bvec;
>+	struct iov_iter iter;
>+
>+	bufsize = 0x100000;
>+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
>+
>+	bvec = kunit_kmalloc_array(test, data.npages, sizeof(*bvec),
>+				   GFP_KERNEL);
>+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, bvec);
>+	k = 0;
>+	for (i = 0; i < data.npages; ++i) {
>+		p = data.pages[i];
>+		if (p == can_merge)
>+			bvec[k-1].bv_len += PAGE_SIZE;
>+		else
>+			bvec_set_page(&bvec[k++], p, PAGE_SIZE, 0);
>+		can_merge = p + 1;
>+	}
>+	iov_iter_bvec(&iter, READ, bvec, k, bufsize);
>+
>+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
>+}
>+
>+static void __init iov_kunit_iter_to_sg_folioq(struct kunit *test)
>+{
>+	struct iov_kunit_iter_to_sg_data data;
>+	struct folio_queue *folioq;
>+	struct iov_iter iter;
>+	size_t bufsize;
>+
>+	bufsize = 0x100000;
>+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
>+
>+	folioq = iov_kunit_create_folioq(test);
>+	iov_kunit_load_folioq(test, &iter, READ, folioq, data.pages,
>+			      data.npages);
>+
>+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
>+}
>+
>+static void __init iov_kunit_iter_to_sg_xarray(struct kunit *test)
>+{
>+	struct iov_kunit_iter_to_sg_data data;
>+	struct xarray *xarray;
>+	struct iov_iter iter;
>+	size_t bufsize;
>+
>+	bufsize = 0x100000;
>+	iov_kunit_iter_to_sg_init(test, bufsize, &data);
>+
>+	xarray = iov_kunit_create_xarray(test);
>+	iov_kunit_load_xarray(test, &iter, READ, xarray, data.pages,
>+			      data.npages);
>+
>+	iov_kunit_iter_to_sg_check(test, &iter, bufsize, &data);
>+}
>+
> static struct kunit_case __refdata iov_kunit_cases[] = {
> 	KUNIT_CASE(iov_kunit_copy_to_kvec),
> 	KUNIT_CASE(iov_kunit_copy_from_kvec),
>@@ -1027,6 +1175,10 @@ static struct kunit_case __refdata iov_kunit_cases[] = {
> 	KUNIT_CASE(iov_kunit_extract_pages_bvec),
> 	KUNIT_CASE(iov_kunit_extract_pages_folioq),
> 	KUNIT_CASE(iov_kunit_extract_pages_xarray),
>+	KUNIT_CASE(iov_kunit_iter_to_sg_kvec),
>+	KUNIT_CASE(iov_kunit_iter_to_sg_bvec),
>+	KUNIT_CASE(iov_kunit_iter_to_sg_folioq),
>+	KUNIT_CASE(iov_kunit_iter_to_sg_xarray),
> 	{}
> };
> 



Good enough, my reviewed by isn't affected


V/R


Josh Law

Josh Law <objecting@objecting.org> wrote:

>     if (memcmp(data->buffer, data->scratch, bufsize)) {

If you do this, please do "memcmp(...) != 0".  It's not a boolean function and
the sense is effectively inverted.

David

On 24 March 2026 23:14:31 GMT, David Howells <dhowells@redhat.com> wrote:
>Josh Law <objecting@objecting.org> wrote:
>
>>     if (memcmp(data->buffer, data->scratch, bufsize)) {
>
>If you do this, please do "memcmp(...) != 0".  It's not a boolean function and
>the sense is effectively inverted.
>
>David
>


Oh yeah, good catch. My mistake

Yeah, David is right


V/R


Josh Law