[Qemu-devel] win7 boot failure with commit f68ec83 - ide: Set BSY bit during FLUSH

["Michael S. Tsirkin" <mst@redhat.com>]

Hi!
I am using this command line:
qemu-system-x86_64 -m 512 -enable-kvm -drive
id=disk,file=./images/win7-x86.qcow2,if=none -device ahci,id=ahci
-device ide-drive,drive=disk,bus=ahci.0 -cdrom
./images/en_windows_7_ultimate_x86_dvd_x15-65921.iso  -monitor stdio
-cpu kvm64 -snapshot

and windows 7 does not boot.
This happens starting from this commit:

commit f68ec8379e88502b4841a110c070e9b118d3151c
Author: Andreas Färber <afaerber@suse.de>
Date:   Wed Jun 5 15:17:57 2013 +0200

    ide: Set BSY bit during FLUSH
    
    The implementation of the ATA FLUSH command invokes a flush at the block
    layer, which may on raw files on POSIX entail a synchronous fdatasync().
    This may in some cases take so long that the SLES 11 SP1 guest driver
    reports I/O errors and filesystems get corrupted or remounted read-only.
    
    Avoid this by setting BUSY_STAT, so that the guest is made aware we are
    in the middle of an operation and no ATA commands are attempted to be
    processed concurrently.
    
    Addresses BNC#637297.
    
    Suggested-by: Gonglei (Arei) <arei.gonglei@huawei.com>
    Signed-off-by: Andreas Färber <afaerber@suse.de>
    Signed-off-by: Kevin Wolf <kwolf@redhat.com>
    Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>


guest starts booting but never completes boot - it just keeps flashing
the flag image.  Boots fine with previous commit:
commit c27d565604038c1572b16dd1cd06e277e6ef02e2

However, reverting f68ec8379e88502b4841a110c070e9b118d3151c on
current master still has the hang on boot
behaviour - possibly a separate issue, I'll have to redo the bisect
to find out.

-- 
MST