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Re: [Qemu-devel] [PATCH] scsi: esp: clean up handle_ti/esp_do_dma if s->
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH] scsi: esp: clean up handle_ti/esp_do_dma if s->do_cmd |
Date: |
Wed, 15 Jun 2016 15:16:22 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
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 <address@hidden>
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 <address@hidden>
> ---
> 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;
> }
> }
>
>