Re: [Qemu-devel] [PATCH v2 1/9] ccid-card-passthru: Move assertion in read() to can_read()

[Marc-André Lureau]

Hi

On Thu, Feb 14, 2019 at 9:19 PM Philippe Mathieu-Daudé
<address@hidden> wrote:
>
> chardev::read() depends of what chardev::can_read() returns, move the
> assertion to can_read().
>
> Suggested-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>

Moving to can_read() makes sense, because nothing (except the chardev
BREAK event) should update vscard_in_pos between the can_read() and
read() callback.

Changing the condition from < to <= could use some explanation. The
can_read() callback should handle the case where the vscard_in buffer
is full (adding = is necessary). And the read() callback should not be
called with size == 0, when card->vscard_in_pos == VSCARD_IN_SIZE (no
data to read).

But it wouldn't harm to leave the existing assert().

Reviewed-by: Marc-André Lureau <address@hidden>





> ---
>  hw/usb/ccid-card-passthru.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/hw/usb/ccid-card-passthru.c b/hw/usb/ccid-card-passthru.c
> index 0a6c657228..8bb1314f49 100644
> --- a/hw/usb/ccid-card-passthru.c
> +++ b/hw/usb/ccid-card-passthru.c
> @@ -116,8 +116,8 @@ static int ccid_card_vscard_can_read(void *opaque)
>  {
>      PassthruState *card = opaque;
>
> -    return VSCARD_IN_SIZE >= card->vscard_in_pos ?
> -           VSCARD_IN_SIZE - card->vscard_in_pos : 0;
> +    assert(card->vscard_in_pos <= VSCARD_IN_SIZE);
> +    return VSCARD_IN_SIZE - card->vscard_in_pos;
>  }
>
>  static void ccid_card_vscard_handle_init(
> @@ -282,7 +282,6 @@ static void ccid_card_vscard_read(void *opaque, const 
> uint8_t *buf, int size)
>          ccid_card_vscard_drop_connection(card);
>          return;
>      }
> -    assert(card->vscard_in_pos < VSCARD_IN_SIZE);
>      assert(card->vscard_in_hdr < VSCARD_IN_SIZE);
>      memcpy(card->vscard_in_data + card->vscard_in_pos, buf, size);
>      card->vscard_in_pos += size;
> --
> 2.20.1
>