[Qemu-devel] [PATCH v4] floppy: save and restore DIR register

[Jason Wang <jasowang@redhat.com>]

We need to keep DIR register unchanged across migration, but currently it
depends on the media_changed flags from block layer. Since we do not
save/restore it and the bdrv_open() called in dest node may set the
media_changed flag when trying to open floppy image, guest driver may think the
floppy have changed after migration. To fix this, a new filed media_changed in
FDrive strcutre was introduced in order to save and restore the it from block
layer through pre_save/post_load callbacks.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---

Changed from V3:
According to Juan's suggestions, back to v2 and just add the checking for
media_changed "changed" in .needed.
Do not fail the migration when src have a drive but dest does not, we can treat
it as user ejected the floppy.

Changed from V2:
According to Paolo's suggestions, a default_migration_media_changed property was
added to avoid saving subsections as much as possible. Its was set media_changed
in pre_load callback and then we can avoid the saving when it was equal to the
media_changed when migrating the FDrive. Behaviors of elder machine types are
also kept through compat_props.

Changed from V1:
Check the drive->bs during post_load.

 hw/fdc.c |   51 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 50 insertions(+), 1 deletions(-)

diff --git a/hw/fdc.c b/hw/fdc.c
index 9fdbc75..edf0360 100644
--- a/hw/fdc.c
+++ b/hw/fdc.c
@@ -36,6 +36,7 @@
 #include "qdev-addr.h"
 #include "blockdev.h"
 #include "sysemu.h"
+#include "block_int.h"
 
 /********************************************************/
 /* debug Floppy devices */
@@ -82,6 +83,7 @@ typedef struct FDrive {
     uint8_t max_track;        /* Nb of tracks           */
     uint16_t bps;             /* Bytes per sector       */
     uint8_t ro;               /* Is read-only           */
+    uint8_t media_changed;    /* Is media changed       */
 } FDrive;
 
 static void fd_init(FDrive *drv)
@@ -533,16 +535,63 @@ static CPUWriteMemoryFunc * const fdctrl_mem_write_strict[3] = {
     NULL,
 };
 
+static void fdrive_media_changed_pre_save(void *opaque)
+{
+    FDrive *drive = opaque;
+
+    drive->media_changed = drive->bs->media_changed;
+}
+
+static int fdrive_media_changed_post_load(void *opaque, int version_id)
+{
+    FDrive *drive = opaque;
+
+    if (drive->bs != NULL) {
+        drive->bs->media_changed = drive->media_changed;
+    }
+
+    /* User ejected the floppy when drive->bs == NULL */
+    return 0;
+}
+
+static bool fdrive_media_changed_needed(void *opaque)
+{
+    FDrive *drive = opaque;
+
+    return (drive->bs != NULL && drive->bs->media_changed != 1);
+}
+
+static const VMStateDescription vmstate_fdrive_media_changed = {
+    .name = "fdrive/media_changed",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .pre_save = fdrive_media_changed_pre_save,
+    .post_load = fdrive_media_changed_post_load,
+    .fields      = (VMStateField[]) {
+        VMSTATE_UINT8(media_changed, FDrive),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_fdrive = {
     .name = "fdrive",
     .version_id = 1,
     .minimum_version_id = 1,
     .minimum_version_id_old = 1,
-    .fields      = (VMStateField []) {
+    .fields      = (VMStateField[]) {
         VMSTATE_UINT8(head, FDrive),
         VMSTATE_UINT8(track, FDrive),
         VMSTATE_UINT8(sect, FDrive),
         VMSTATE_END_OF_LIST()
+    },
+    .subsections = (VMStateSubsection[]) {
+        {
+            .vmsd = &vmstate_fdrive_media_changed,
+            .needed = &fdrive_media_changed_needed,
+        } , {
+            /* empty */
+        }
     }
 };
 
-- 
1.7.1