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Re: [Qemu-devel] [PATCH v2] fdc: fix media change detection for windows

From: Pavel Hrdina
Subject: Re: [Qemu-devel] [PATCH v2] fdc: fix media change detection for windows
Date: Wed, 06 Jun 2012 15:43:14 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1

On 06/06/2012 12:35 PM, Kevin Wolf wrote:
Am 05.06.2012 18:34, schrieb Pavel Hrdina:
On 06/05/2012 05:56 PM, Kevin Wolf wrote:
Am 05.06.2012 17:50, schrieb Pavel Hrdina:
Sorry, I forget the qtest. I'll create it and send it again.


On 06/05/2012 05:46 PM, Pavel Hrdina wrote:
The Windows uses 'READ' command at the start of an instalation
without checking the 'dir' register. We have to abort the transfer
with an abnormal termination if there is no media in the drive.

We have to also check the 'media_change' bit in the 'fd_seek'. This
internal seek clears the 'media_change' bit, too, if there is
a media inserted.

Signed-off-by: Pavel Hrdina<address@hidden>
   hw/fdc.c |    7 ++++++-
   1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/hw/fdc.c b/hw/fdc.c
index 30d34e3..2d6dd30 100644
--- a/hw/fdc.c
+++ b/hw/fdc.c
@@ -127,8 +127,13 @@ static int fd_seek(FDrive *drv, uint8_t head, uint8_t track, uint8_t sect,
       uint32_t sector;
       int ret;

+    if (drv->bs != NULL&&   bdrv_is_inserted(drv->bs)) {
+        drv->media_changed = 0;
+    }
       if (track>   drv->max_track ||
-        (head != 0&&   (drv->flags&   FDISK_DBL_SIDES) == 0)) {
+        (head != 0&&   (drv->flags&   FDISK_DBL_SIDES) == 0) ||
+        drv->media_changed) {
Why not directly use bdrv_is_inserted() here?

Fiddling around with media_changed feels rather hacky and is strictly
speaking incorrect because a step pulse is not guaranteed to happen in
the following code. The floppy code doesn't get it quite right today
anyway, but a hack like this would contribute to the problem.

           FLOPPY_DPRINTF("try to read %d %02x %02x (max=%d %d %02x %02x)\n",
                          head, track, sect, 1,
                          (drv->flags&   FDISK_DBL_SIDES) == 0 ? 0 : 1,

I'll move the code into the end of 'fd_seek' function, where a step is 
guaranteed. Internal seek should also reset the 'media_changed' bit if 
there is a media in the drive. I'll create the qtest tomorrow then I'll 
send another version of this patch.
My point is that the success of a seek has nothing to do with the DSKCHG
signal. Even if you move the code around, DSKCHG may start to coincide
with the condition you really want to check, but it's logically still
not what should be checked. What's wrong with !bdrv_is_inserted() in the
if condition?

If something is wrong with the media_changed handling, then it's a
separate bug that should be dealt with in a separate patch.

I don't think that is true. Please read this http://wiki.osdev.org/Floppy_Disk_Controller#DIR_register.2C_Disk_Change_bit and http://wiki.osdev.org/Floppy_Disk_Controller#Seek . Directly it has nothing to do with DSKCHG bit, but indirectly seek to different cylinder fails if there is no media in drive on real FDC. Only successful seek to different cylinder clears the DSKCHG bit.

That's why I do it this way, because in our FDC emulation we clears the DSKCHG bit or not also if you seek to the same cylinder. The function 'fd_seek' stands for implied seek which also clears the DSKCHG bit.


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