[PATCH blktests] block/045: respect dma_alignment

Since the kernel commit 14b007e17881 ("block: validate user space
vectors during extraction"), the test case block/045 fails with the
error message below:

 block/045 (test direct I/O full-trim bvec alignment)         [failed]
     runtime  0.550s  ...  0.630s
     --- tests/block/045.out     2026-08-03 19:26:40.407053612 +0900
     +++ /home/shin/Blktests/blktests/results/nodev/block/045.out.bad    2026-08-05 20:48:33.366932845 +0900
     @@ -1,2 +1,4 @@
      Running block/045
     +bio-full-trim: pread returned -1 (errno 22)
     +bio-full-trim helper failed
      Test complete

The errno 22 means EINVAL. The commit introduced the dma_alignment check
and returns EINVAL when the check is not fulfilled. The test case calls
pread() with one byte offset. This offset is not aligned to the
dma_alignment, then EINVAL is returned.

To avoid the failure, respect the dma_alignment check. Get the
dma_alignment value and pass it to bio-full-trim command. Use the
alignment to decide the offset value.

Link: https://lore.kernel.org/linux-block/anMscoGkR5BYjSGy@shinmob/
Signed-off-by: Shin'ichiro Kawasaki <[email protected]>
---
I confirmed that block/045 can detect the KASAN stack-out-of-bounds
that was caused by the v1 kernel patch titled "block: fix aligning of
bounced dio read bios" [*], regardless of whether this blktests patch
is applied or not.

[*] https://lore.kernel.org/linux-block/[email protected]/

 src/bio-full-trim.c | 27 +++++++++++++++++++++++++--
 tests/block/045     |  3 ++-
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/bio-full-trim.c b/src/bio-full-trim.c
index e304b2c..a3dda4c 100644
--- a/src/bio-full-trim.c
+++ b/src/bio-full-trim.c
@@ -12,26 +12,49 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+static int msb(unsigned int v)
+{
+	unsigned int b = 0;
+
+	while (v >>= 1)
+		b++;
+
+	return b;
+}
+
 int main(int argc, char **argv)
 {
 	unsigned int block_size;
 	unsigned char *p;
 	long page_size;
+	unsigned int dma_alignment;
+	unsigned int dma_aligned_offset;
 	ssize_t ret;
 	int fd;
 
-	if (argc != 2)
+	if (argc != 3)
 		return EXIT_FAILURE;
+
 	page_size = sysconf(_SC_PAGESIZE);
 	if (page_size <= 0)
 		errx(EXIT_FAILURE, "invalid page size");
 
+	dma_alignment = atoi(argv[2]);
+	if (dma_alignment == 0)
+		errx(EXIT_FAILURE, "unexpected dma_alignment");
+
 	fd = open(argv[1], O_RDONLY | O_DIRECT);
 	if (fd < 0)
 		err(EXIT_FAILURE, "open %s", argv[1]);
 	if (ioctl(fd, BLKSSZGET, &block_size))
 		err(EXIT_FAILURE, "BLKSSZGET");
 
+	dma_aligned_offset = 1 << (msb(dma_alignment) + 1);
+	if (dma_aligned_offset >= block_size)
+		errx(EXIT_FAILURE,
+		     "unexpected dma_alignment %u for block size %u",
+		     dma_alignment, block_size);
+
 	p = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE,
 		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 	if (p == MAP_FAILED)
@@ -40,7 +63,7 @@ int main(int argc, char **argv)
 		err(EXIT_FAILURE, "mprotect");
 
 	errno = 0;
-	ret = pread(fd, p + page_size - 1, block_size, 0);
+	ret = pread(fd, p + page_size - dma_aligned_offset, block_size, 0);
 	if (ret == -1 && errno == EFAULT)
 		return EXIT_SUCCESS;
 	errx(EXIT_FAILURE, "pread returned %zd (errno %d)", ret, errno);
diff --git a/tests/block/045 b/tests/block/045
index 65bfcb9..6e112b6 100755
--- a/tests/block/045
+++ b/tests/block/045
@@ -25,7 +25,8 @@ test() {
 		return 1
 	fi
 
-	if ! src/bio-full-trim /dev/nullb1; then
+	if ! src/bio-full-trim /dev/nullb1 \
+	     $(< /sys/block/nullb1/queue/dma_alignment); then
 		echo "bio-full-trim helper failed"
 	fi
 
-- 
2.54.0