Re: [Qemu-block] [PATCH 1/4] IDE: Do not flush empty CDROM drives

[Stefan Hajnoczi]

On Tue, Aug 08, 2017 at 01:57:08PM -0400, John Snow wrote:
> The block backend changed in a way that flushing empty CDROM drives
> is now an error. Amend IDE to avoid doing so until the root problem
> can be addressed for 2.11.
> 
> Reported-by: Kieron Shorrock 
> Signed-off-by: John Snow 
> ---
>  hw/ide/core.c | 11 +++
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index 0b48b64..6cbca43 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -1053,17 +1053,21 @@ static void ide_flush_cb(void *opaque, int ret)
>  ide_set_irq(s->bus);
>  }
>  
> -static void ide_flush_cache(IDEState *s)
> +static bool ide_flush_cache(IDEState *s)

Previously this function invoked ide_flush_cb() to complete the request
and raise an IRQ.  Now it may return true instead of invoking
ide_flush_cb().  It's no longer a helper function, it's more like an IDE
command handler.

cmd_set_features() must be updated:

  case 0x82: /* write cache disable */
  blk_set_enable_write_cache(s->blk, false);
  identify_data = (uint16_t *)s->identify_data;
  put_le16(identify_data + 85, (1 << 14) | 1);
  ide_flush_cache(s);
  return false;  <--- should be "return ide_flush_cache(s)"

To make the code clearer I suggest deleting ide_flush_cache() and
calling cmd_flush_cache() directly instead.  That way it's obvious that
this is an IDE command handler and it may return true to indicate the
the command completed immediately.

>  {
>  if (s->blk == NULL) {
>  ide_flush_cb(s, 0);
> -return;
> +return false;
> +} else if (!blk_bs(s->blk)) {
> +/* Nothing to flush */

Please move information from the commit description into this comment if
you respin.  Someone looking at the code might think this is a nop that
is safe to remove.  Once blk_*() is fixed this code path can be removed
again.


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[Qemu-block] [PATCH 1/4] IDE: Do not flush empty CDROM drives

[John Snow]

The block backend changed in a way that flushing empty CDROM drives
is now an error. Amend IDE to avoid doing so until the root problem
can be addressed for 2.11.

Reported-by: Kieron Shorrock 
Signed-off-by: John Snow 
---
 hw/ide/core.c | 11 +++
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/hw/ide/core.c b/hw/ide/core.c
index 0b48b64..6cbca43 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -1053,17 +1053,21 @@ static void ide_flush_cb(void *opaque, int ret)
 ide_set_irq(s->bus);
 }
 
-static void ide_flush_cache(IDEState *s)
+static bool ide_flush_cache(IDEState *s)
 {
 if (s->blk == NULL) {
 ide_flush_cb(s, 0);
-return;
+return false;
+} else if (!blk_bs(s->blk)) {
+/* Nothing to flush */
+return true;
 }
 
 s->status |= BUSY_STAT;
 ide_set_retry(s);
 block_acct_start(blk_get_stats(s->blk), &s->acct, 0, BLOCK_ACCT_FLUSH);
 s->pio_aiocb = blk_aio_flush(s->blk, ide_flush_cb, s);
+return false;
 }
 
 static void ide_cfata_metadata_inquiry(IDEState *s)
@@ -1508,8 +1512,7 @@ static bool cmd_write_dma(IDEState *s, uint8_t cmd)
 
 static bool cmd_flush_cache(IDEState *s, uint8_t cmd)
 {
-ide_flush_cache(s);
-return false;
+return ide_flush_cache(s);
 }
 
 static bool cmd_seek(IDEState *s, uint8_t cmd)
-- 
2.9.4