Re: [PATCH] usb: allow max 8192 bytes for desc

[Peter Maydell]

On Tue, 11 Jan 2022 at 10:54, zhenwei pi <pizhenwei@bytedance.com> wrote:
>
> A device of USB video class usually uses larger desc structure, so
> use larger buffer to avoid failure. (dev-video.c is ready)
>
> Allocating memory dynamically by g_malloc of the orignal version of
> this change, Philippe suggested just using the stack. Test the two
> versions of qemu binary, the size of stack gets no change.
>
> CC: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>  hw/usb/desc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/usb/desc.c b/hw/usb/desc.c
> index 8b6eaea407..57d2aedba1 100644
> --- a/hw/usb/desc.c
> +++ b/hw/usb/desc.c
> @@ -632,7 +632,7 @@ int usb_desc_get_descriptor(USBDevice *dev, USBPacket *p,
>      bool msos = (dev->flags & (1 << USB_DEV_FLAG_MSOS_DESC_IN_USE));
>      const USBDesc *desc = usb_device_get_usb_desc(dev);
>      const USBDescDevice *other_dev;
> -    uint8_t buf[256];
> +    uint8_t buf[8192];
>      uint8_t type = value >> 8;
>      uint8_t index = value & 0xff;
>      int flags, ret = -1;

I think 8K is too large to be allocating as an array on
the stack, so if we need this buffer to be larger we should
switch to some other allocation strategy for it.

thanks
-- PMM