[Qemu-devel] [PULL 02/42] atapi migration: Throw recoverable error to avoid recovery

[Kevin Wolf <kwolf@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

(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>
---
 hw/ide/atapi.c    | 17 +++++++++++++++++
 hw/ide/internal.h |  2 ++
 hw/ide/pci.c      | 11 +++++++++++
 3 files changed, 30 insertions(+)

diff --git a/hw/ide/atapi.c b/hw/ide/atapi.c
index a71e6e0..1bf8b34 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)
 {
diff --git a/hw/ide/internal.h b/hw/ide/internal.h
index c998003..ee9a57f 100644
--- a/hw/ide/internal.h
+++ b/hw/ide/internal.h
@@ -289,6 +289,7 @@ typedef struct IDEDMAOps IDEDMAOps;
 #define ATAPI_INT_REASON_TAG            0xf8
 
 /* same constants as bochs */
+#define ASC_NO_SEEK_COMPLETE                 0x02
 #define ASC_ILLEGAL_OPCODE                   0x20
 #define ASC_LOGICAL_BLOCK_OOR                0x21
 #define ASC_INV_FIELD_IN_CMD_PACKET          0x24
@@ -530,6 +531,7 @@ void ide_dma_error(IDEState *s);
 
 void ide_atapi_cmd_ok(IDEState *s);
 void ide_atapi_cmd_error(IDEState *s, int sense_key, int asc);
+void ide_atapi_dma_restart(IDEState *s);
 void ide_atapi_io_error(IDEState *s, int ret);
 
 void ide_ioport_write(void *opaque, uint32_t addr, uint32_t val);
diff --git a/hw/ide/pci.c b/hw/ide/pci.c
index bee5ad3..e3f2054 100644
--- a/hw/ide/pci.c
+++ b/hw/ide/pci.c
@@ -235,6 +235,17 @@ static void bmdma_restart_bh(void *opaque)
         }
     } else if (error_status & IDE_RETRY_FLUSH) {
         ide_flush_cache(bmdma_active_if(bm));
+    } else {
+        IDEState *s = bmdma_active_if(bm);
+
+        /*
+         * We've not got any bits to tell us about ATAPI - but
+         * we do have the end_transfer_func that tells us what
+         * we're trying to do.
+         */
+        if (s->end_transfer_func == ide_atapi_cmd) {
+            ide_atapi_dma_restart(s);
+        }
     }
 }
 
-- 
1.8.3.1