Re: [PATCH 2/4] hw/block/fdc: Remove the check_media_rate property

[John Snow]

On 2/5/21 1:37 AM, Thomas Huth wrote:
On 05/02/2021 01.40, John Snow wrote:
On 2/3/21 12:18 PM, Thomas Huth wrote:
This was only required for the pc-1.0 and earlier machine types.
Now that these have been removed, we can also drop the corresponding
code from the FDC device.
Signed-off-by: Thomas Huth <th...@redhat.com>
---
  hw/block/fdc.c             | 17 ++---------------
  tests/qemu-iotests/172.out | 35 -----------------------------------
  2 files changed, 2 insertions(+), 50 deletions(-)

diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index 292ea87805..198940e737 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -874,7 +874,6 @@ struct FDCtrl {
          FloppyDriveType type;
      } qdev_for_drives[MAX_FD];
      int reset_sensei;
-    uint32_t check_media_rate;

I am a bit of a dunce when it comes to the compatibility properties... 
does this mess with the migration format?

I guess it doesn't, since it's not in the VMSTATE declaration.

Hmmmm, alright.

I think that should be fine, yes.

      FloppyDriveType fallback; /* type=auto failure fallback */
      /* Timers state */
      uint8_t timer0;
@@ -1021,18 +1020,10 @@ static const VMStateDescription 
vmstate_fdrive_media_changed = {
      }
  };
-static bool fdrive_media_rate_needed(void *opaque)
-{
-    FDrive *drive = opaque;
-
-    return drive->fdctrl->check_media_rate;
-}
-
  static const VMStateDescription vmstate_fdrive_media_rate = {
      .name = "fdrive/media_rate",
      .version_id = 1,
      .minimum_version_id = 1,
-    .needed = fdrive_media_rate_needed,
      .fields = (VMStateField[]) {
          VMSTATE_UINT8(media_rate, FDrive),
          VMSTATE_END_OF_LIST()
@@ -1689,8 +1680,7 @@ static void fdctrl_start_transfer(FDCtrl 
*fdctrl, int direction)
      /* Check the data rate. If the programmed data rate does not match
       * the currently inserted medium, the operation has to fail. */
-    if (fdctrl->check_media_rate &&
-        (fdctrl->dsr & FD_DSR_DRATEMASK) != cur_drv->media_rate) {
+    if ((fdctrl->dsr & FD_DSR_DRATEMASK) != cur_drv->media_rate) {
          FLOPPY_DPRINTF("data rate mismatch (fdc=%d, media=%d)\n",
                         fdctrl->dsr & FD_DSR_DRATEMASK, 
cur_drv->media_rate);
          fdctrl_stop_transfer(fdctrl, FD_SR0_ABNTERM, FD_SR1_MA, 0x00);
@@ -2489,8 +2479,7 @@ static void fdctrl_result_timer(void *opaque)
          cur_drv->sect = (cur_drv->sect % cur_drv->last_sect) + 1;
      }
      /* READ_ID can't automatically succeed! */
-    if (fdctrl->check_media_rate &&
-        (fdctrl->dsr & FD_DSR_DRATEMASK) != cur_drv->media_rate) {
+    if ((fdctrl->dsr & FD_DSR_DRATEMASK) != cur_drv->media_rate) {
          FLOPPY_DPRINTF("read id rate mismatch (fdc=%d, media=%d)\n",
                         fdctrl->dsr & FD_DSR_DRATEMASK, 
cur_drv->media_rate);
          fdctrl_stop_transfer(fdctrl, FD_SR0_ABNTERM, FD_SR1_MA, 0x00);
@@ -2895,8 +2884,6 @@ static Property isa_fdc_properties[] = {
      DEFINE_PROP_UINT32("dma", FDCtrlISABus, dma, 2),
      DEFINE_PROP_DRIVE("driveA", FDCtrlISABus, 
state.qdev_for_drives[0].blk),
      DEFINE_PROP_DRIVE("driveB", FDCtrlISABus, 
state.qdev_for_drives[1].blk),
-    DEFINE_PROP_BIT("check_media_rate", FDCtrlISABus, 
state.check_media_rate,
-                    0, true),

Could you theoretically set this via QOM commands in QMP, and claim 
that this is a break in behavior?

Though, it's ENTIRELY undocumented, so ... it's probably fine, I 
think. Probably. (Please soothe my troubled mind.)

A user actually could mess with this property even on the command line, 
e.g. by using:

  qemu-system-x86_64 -global isa-fdc.check_media_rate=false

... but, as you said, it's completely undocumented, the property is 
really just there for the internal use of machine type compatibility. 
We've done such clean-ups in the past already, see e.g. 
c6026998eef382d7ad76 or 2a4dbaf1c0db2453ab78f, so I think this should be 
fine. But if you disagree, I could replace this by a patch that adds 
this property to the list of deprecated features instead, so we could at 
least remove it after it has been deprecated for two releases?


I don't think it's necessary, personally -- just wanted to make sure I 
knew the exact stakes here.

Reviewed-by: John Snow <js...@redhat.com>
Acked-by: John Snow <js...@redhat.com>