[PATCH] block: Return the soft block size for compat BLKBSZGET

[PATCH] block: Return the soft block size for compat BLKBSZGET

[Hungyu Lin]

BLKBSZGET returns the block device's soft block size, while BLKSSZGET
returns its logical sector size. The compat BLKBSZGET_32 handler uses
bdev_logical_block_size(), so it returns the wrong value when these
sizes differ.

For example, on an x86_64 kernel a native query of a RAM or loop device
with 512-byte logical sectors returns the initial soft block size of
4096 bytes, but an i386 process gets 512 bytes. This makes 32-bit
blockdev --getbsz and the BSZ column of --report disagree with native
queries, even without a preceding BLKBSZSET.

Use block_size() as the native handler and the pre-regression compat
handler do, and correct the case comment to describe the soft size.

Fixes: 9b81648cb5e3 ("compat_ioctl: simplify up block/ioctl.c")
Cc: stable@vger.kernel.org
Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
---
 block/ioctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index 64b4e6c0f696..fb2f4b4d2505 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -835,8 +835,8 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 		return compat_put_ulong(argp, bdev_nr_sectors(bdev));
 
 	/* The data is compatible, but the command number is different */
-	case BLKBSZGET_32: /* get the logical block size (cf. BLKSSZGET) */
-		return put_int(argp, bdev_logical_block_size(bdev));
+	case BLKBSZGET_32: /* get the soft block size (cf. BLKSSZGET) */
+		return put_int(argp, block_size(bdev));
 	case BLKBSZSET_32:
 		return blkdev_bszset(file, mode, argp);
 	case BLKGETSIZE64_32:

base-commit: 734bef548a96e8774d6eef5dfa2026c6edc4e80b
-- 
2.43.0

Re: [PATCH] block: Return the soft block size for compat BLKBSZGET

[Arnd Bergmann]

On Fri, Oct 23, 2026, at 17:36, Hungyu Lin wrote:
> BLKBSZGET returns the block device's soft block size, while BLKSSZGET
> returns its logical sector size. The compat BLKBSZGET_32 handler uses
> bdev_logical_block_size(), so it returns the wrong value when these
> sizes differ.
>
> For example, on an x86_64 kernel a native query of a RAM or loop device
> with 512-byte logical sectors returns the initial soft block size of
> 4096 bytes, but an i386 process gets 512 bytes. This makes 32-bit
> blockdev --getbsz and the BSZ column of --report disagree with native
> queries, even without a preceding BLKBSZSET.
>
> Use block_size() as the native handler and the pre-regression compat
> handler do, and correct the case comment to describe the soft size.
>
> Fixes: 9b81648cb5e3 ("compat_ioctl: simplify up block/ioctl.c")
> Cc: stable@vger.kernel.org
> Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>

Reviewed-by: Arnd Bergmann <arnd@arndb.de>