[Qemu-devel] [PATCH 1/3] ide: don't loose pending dma state

["Denis V. Lunev" <den@openvz.org>]

From: Pavel Butsykin <pbutsykin@virtuozzo.com>

If the migration occurs after the IDE DMA has been set up but before it
has been initiated, the state gets lost upon save/restore. Specifically,
->dma_cb callback gets cleared, so, when the guest eventually starts bus
mastering, the DMA never completes, causing the guest to time out the
operation.

OTOH all the infrastructure is already in place to restart the DMA if
the migration happens while the DMA is in progress.

So reuse that infrastructure, by calling the DMA callback with an
artificial error code in pre_save if the callback is already set but
DMAING is clear. The callback then sets bus->error_status to indicate
the need for restart; however since DMAING is clear the state upon
restore will be exactly "ready forDMA" as before the save.

This patch only fixes the IDE DMA case; the ATAPI DMA is left with a stub
for now since its restart hadn't been implemented yet. It will be
addressed in the followup patch.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: John Snow <jsnow@redhat.com>
---
 hw/ide/atapi.c    | 9 ++++++++-
 hw/ide/core.c     | 9 ++++++++-
 hw/ide/internal.h | 7 +++++++
 hw/ide/pci.c      | 3 +++
 4 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/hw/ide/atapi.c b/hw/ide/atapi.c
index 1fe58ab..268220d 100644
--- a/hw/ide/atapi.c
+++ b/hw/ide/atapi.c
@@ -381,7 +381,14 @@ static void ide_atapi_cmd_read_dma_cb(void *opaque, int ret)
     IDEState *s = opaque;
     int data_offset, n;
 
-    if (ret < 0) {
+    if (ret < 0) { /* XXX: handle -ESTATESAVE for migration */
+        if (ret == -ESTATESAVE) {
+            /*
+             * This case is not really an error
+             * but a request to save the state.
+             */
+            return;
+        }
         ide_atapi_io_error(s, ret);
         goto eot;
     }
diff --git a/hw/ide/core.c b/hw/ide/core.c
index 241e840..872e11f 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -810,7 +810,14 @@ static void ide_dma_cb(void *opaque, int ret)
         else if (s->dma_cmd == IDE_DMA_TRIM)
             op |= IDE_RETRY_TRIM;
 
-        if (ide_handle_rw_error(s, -ret, op)) {
+        if (ret == -ESTATESAVE) {
+            /*
+             * This case is not really an error
+             * but a request to save the state.
+             */
+            s->bus->error_status = op;
+            return;
+        } else if (ide_handle_rw_error(s, -ret, op)) {
             return;
         }
     }
diff --git a/hw/ide/internal.h b/hw/ide/internal.h
index 86bde26..dcd8627 100644
--- a/hw/ide/internal.h
+++ b/hw/ide/internal.h
@@ -513,6 +513,13 @@ struct IDEDevice {
 #define IDE_RETRY_TRIM 0x80
 #define IDE_RETRY_HBA  0x100
 
+/*
+ * a code to trigger entering error path and save/restore the "ready to DMA"
+ * state just like DMA-ing state. (Ab)use EINPROGRESS as it's not supposed to
+ * come from the block layer
+ */
+#define ESTATESAVE EINPROGRESS
+
 static inline IDEState *idebus_active_if(IDEBus *bus)
 {
     return bus->ifs + bus->unit;
diff --git a/hw/ide/pci.c b/hw/ide/pci.c
index 92ffee7..e1f89fa 100644
--- a/hw/ide/pci.c
+++ b/hw/ide/pci.c
@@ -308,6 +308,9 @@ static void ide_bmdma_pre_save(void *opaque)
     BMDMAState *bm = opaque;
     uint8_t abused_bits = BM_MIGRATION_COMPAT_STATUS_BITS;
 
+    if (!(bm->status & BM_STATUS_DMAING) && bm->dma_cb) {
+        bm->dma_cb(bmdma_active_if(bm), -ESTATESAVE);
+    }
     bm->migration_retry_unit = bm->bus->retry_unit;
     bm->migration_retry_sector_num = bm->bus->retry_sector_num;
     bm->migration_retry_nsector = bm->bus->retry_nsector;
-- 
2.1.4