atapi migration: Throw recoverable error to avoid recovery

(With the previous atapi_dma flag recovery)
If migration happens between the ATAPI command being written and the
bmdma being started, the DMA is dropped.  Eventually the guest times
out and recovers, but that can take many seconds.
(This is rare, on a pingpong reading the CD continuously I hit
this about ~1/30-1/50 migrates)

I don't think we've got enough state to be able to recover safely
at this point, so I throw a 'medium error, no seek complete'
that I'm assuming guests will try and recover from an apparently
dirty CD.

OK, it's a hack, the real solution is probably to push a lot of
ATAPI state into the migration stream, but this is a fix that
works with no stream changes. Tested only on Linux (both RHEL5
(pre-libata) and RHEL7).

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/hw/ide/atapi.c b/hw/ide/atapi.c
index a71e6e014f..1bf8b34528 100644
--- a/hw/ide/atapi.c
+++ b/hw/ide/atapi.c
@@ -394,6 +394,23 @@ static void ide_atapi_cmd_read(IDEState *s, int lba, int nb_sectors,
     }
 }
 
+
+/* Called by *_restart_bh when the transfer function points
+ * to ide_atapi_cmd
+ */
+void ide_atapi_dma_restart(IDEState *s)
+{
+    /*
+     * I'm not sure we have enough stored to restart the command
+     * safely, so give the guest an error it should recover from.
+     * I'm assuming most guests will try to recover from something
+     * listed as a medium error on a CD; it seems to work on Linux.
+     * This would be more of a problem if we did any other type of
+     * DMA operation.
+     */
+    ide_atapi_cmd_error(s, MEDIUM_ERROR, ASC_NO_SEEK_COMPLETE);
+}
+
 static inline uint8_t ide_atapi_set_profile(uint8_t *buf, uint8_t *index,
                                             uint16_t profile)
 {