Re: [PATCH v3 4/5] virtio: blk: Fix converting the vendor id to a string

[Kuan-Wei Chiu <visitorckw@gmail.com>]

Hi Daniel,

On Thu, Apr 09, 2026 at 07:09:27AM +0900, Daniel Palmer wrote:
> Currently we are trying to work out if the vendor id is from
> a virtio-mmio device and then casting a u32 to a char* and using
> it as a C-string. By chance there is usually a zero after the u32
> and it works.
> 
> Since the vendor id we are trying to convert to a string is QEMU's
> just define a value for the QEMU vendor id, check if the vendor
> id matches and then use a predefined string for "QEMU".
> 
> I don't think we should have been assumming all virtio-mmio vendor
> ids are printable ASCII chars in the first place so do this special
> casing just for QEMU. If the vendor id isn't QEMU print the hex
> value of it.
> 
> Signed-off-by: Daniel Palmer <daniel@thingy.jp>
> ---
>  drivers/virtio/virtio_blk.c | 12 +++++-------
>  include/virtio_mmio.h       |  2 ++
>  2 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> index 3dd0cf36268b..d876c40deb05 100644
> --- a/drivers/virtio/virtio_blk.c
> +++ b/drivers/virtio/virtio_blk.c
> @@ -11,6 +11,7 @@
>  #include <part.h>
>  #include <virtio_types.h>
>  #include <virtio.h>
> +#include <virtio_mmio.h>
>  #include <virtio_ring.h>
>  #include <linux/log2.h>
>  #include "virtio_blk.h"
> @@ -164,14 +165,11 @@ static int virtio_blk_bind(struct udevice *dev)
>  		return devnum;
>  	desc->devnum = devnum;
>  	desc->part_type = PART_TYPE_UNKNOWN;
> -	/*
> -	 * virtio mmio transport supplies string identification for us,
> -	 * while pci trnasport uses a 2-byte subvendor value.
> -	 */
> -	if (uc_priv->vendor >> 16)
> -		sprintf(desc->vendor, "%s", (char *)&uc_priv->vendor);
> +
> +	if (uc_priv->vendor == VIRTIO_MMIO_VENDOR_QEMU)
> +		strcpy(desc->vendor, "QEMU");

Is there a chance that other non qemu virtio-mmio devices also use a
4 character string for their vendor ID? If so, this patch will regress
their output from a human-readable string to a raw hex value.

Regards,
Kuan-Wei

>  	else
> -		sprintf(desc->vendor, "%04x", uc_priv->vendor);
> +		sprintf(desc->vendor, "%08x", uc_priv->vendor);
>  	desc->bdev = dev;
>  
>  	/* Indicate what driver features we support */
> diff --git a/include/virtio_mmio.h b/include/virtio_mmio.h
> index 8c072826db55..cc59bc516c2c 100644
> --- a/include/virtio_mmio.h
> +++ b/include/virtio_mmio.h
> @@ -5,6 +5,8 @@
>  
>  #include <linux/types.h>
>  
> +#define VIRTIO_MMIO_VENDOR_QEMU	0x554d4551
> +
>  struct virtio_mmio_plat {
>  	phys_addr_t base;
>  };
> -- 
> 2.51.0
>