Re: [Qemu-devel] [PATCH] scsi: esp: clean up handle_ti/esp_do_dma if s->do_cmd

[Laszlo Ersek <lersek@redhat.com>]

On 06/15/16 14:39, Paolo Bonzini wrote:
> Avoid duplicated code between esp_do_dma and handle_ti.  esp_do_dma
> has the same code that handle_ti contains after the call to esp_do_dma;
> but the code in handle_ti is never reached

(... never reached after esp_do_dma() is called -- it is reached in
general... but splitting hairs about this is not important)

> because it is in an "else if".
> Remove the else and also the pointless return.

Yes, this looks correct.

> esp_do_dma also has a partially dead assignment of the to_device
> variable.  Sink it to the point where it's actually used.

You could sink it a bit more, I think, to just before the first use.

> Finally, assert that the other caller of esp_do_dma (esp_transfer_data)
> only transfers data and not a command.  This is true because get_cmd
> cancels the old request synchronously before its caller handle_satn_stop
> sets do_cmd to 1.

I didn't try to verify why the claim is true, but if the claim is true,
then the assert() is valid, and fits in with the changes in esp_do_dma()
and handle_ti() -- the logic taken over by handle_ti() from esp_do_dma()
is not reached when esp_do_dma() is called by esp_transfer_data(), but
then again, on that call path, the original logic was never reached anyway.

(If the claim is wrong, we'll quickly find out with the assert() :))

... So, I think if you wish, you could lower the "to_device" assignment
a bit more. Either way:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

And I guess Prasad will submit a new version of the buffer overflow fix,
on top of this patch, according to your previous message
<http://thread.gmane.org/gmane.comp.emulators.qemu/419113/focus=419155>.

Thanks
Laszlo

> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  hw/scsi/esp.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index 3f08598..2bc5076 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -245,21 +245,17 @@ static void esp_do_dma(ESPState *s)
>      uint32_t len;
>      int to_device;
>  
> -    to_device = (s->ti_size < 0);
>      len = s->dma_left;
>      if (s->do_cmd) {
>          trace_esp_do_dma(s->cmdlen, len);
>          s->dma_memory_read(s->dma_opaque, &s->cmdbuf[s->cmdlen], len);
> -        s->ti_size = 0;
> -        s->cmdlen = 0;
> -        s->do_cmd = 0;
> -        do_cmd(s, s->cmdbuf);
>          return;
>      }
>      if (s->async_len == 0) {
>          /* Defer until data is available.  */
>          return;
>      }
> +    to_device = (s->ti_size < 0);
>      if (len > s->async_len) {
>          len = s->async_len;
>      }
> @@ -318,6 +314,7 @@ void esp_transfer_data(SCSIRequest *req, uint32_t len)
>  {
>      ESPState *s = req->hba_private;
>  
> +    assert(!s->do_cmd);
>      trace_esp_transfer_data(s->dma_left, s->ti_size);
>      s->async_len = len;
>      s->async_buf = scsi_req_get_buf(req);
> @@ -358,13 +355,13 @@ static void handle_ti(ESPState *s)
>          s->dma_left = minlen;
>          s->rregs[ESP_RSTAT] &= ~STAT_TC;
>          esp_do_dma(s);
> -    } else if (s->do_cmd) {
> +    }
> +    if (s->do_cmd) {
>          trace_esp_handle_ti_cmd(s->cmdlen);
>          s->ti_size = 0;
>          s->cmdlen = 0;
>          s->do_cmd = 0;
>          do_cmd(s, s->cmdbuf);
> -        return;
>      }
>  }
>  
>