[Qemu-devel] [PATCH 4/5] Reopen files after migration

[Juan Quintela]

We need to invalidate the Read Cache on the destination, otherwise we
have corruption.  Easy way to reproduce it is:

- create an qcow2 images
- start qemu on destination of migration (qemu .... -incoming tcp:...)
- start qemu on source of migration and do one install.
- migrate at the end of install (when lot of disk IO has happened).

Destination of migration has a local copy of the L1/L2 tables that existed
at the beginning, before the install started.  We have disk corruption at
this point.  The solution (for NFS) is to just re-open the file.  Operations
have to happen in this order:

- source of migration: flush()
- destination: close(file);
- destination: open(file)

it is not necesary that source of migration close the file.

Signed-off-by: Juan Quintela <address@hidden>
---
 blockdev.c  |   42 +++++++++++++++++++++++++++++++++++++-----
 blockdev.h  |    6 ++++++
 migration.c |    6 ++++++
 3 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index f9bb659..3f3df7a 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -116,6 +116,7 @@ void drive_uninit(DriveInfo *dinfo)
     bdrv_delete(dinfo->bdrv);
     QTAILQ_REMOVE(&drives, dinfo, next);
     qemu_free(dinfo->id);
+    qemu_free(dinfo->file);
     qemu_free(dinfo);
 }

@@ -136,6 +137,36 @@ static int parse_block_error_action(const char *buf, int 
is_read)
     }
 }

+static int drive_open(DriveInfo *dinfo)
+{
+    int res = bdrv_open(dinfo->bdrv, dinfo->file, dinfo->bdrv_flags, 
dinfo->drv);
+
+    if (res < 0) {
+        fprintf(stderr, "qemu: could not open disk image %s: %s\n",
+                        dinfo->file, strerror(errno));
+    }
+    return res;
+}
+
+int drives_reinit(void)
+{
+    DriveInfo *dinfo;
+
+    QTAILQ_FOREACH(dinfo, &drives, next) {
+        if (dinfo->opened && !bdrv_is_read_only(dinfo->bdrv)) {
+            int res;
+            bdrv_close(dinfo->bdrv);
+            res = drive_open(dinfo);
+            if (res) {
+                   fprintf(stderr, "qemu: re-open of %s failed wth error %d\n",
+                           dinfo->file, res);
+                   return res;
+           }
+        }
+    }
+    return 0;
+}
+
 DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi, int *fatal_error)
 {
     const char *buf;
@@ -156,7 +187,6 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi, 
int *fatal_error)
     const char *devaddr;
     DriveInfo *dinfo;
     int snapshot = 0;
-    int ret;

     *fatal_error = 1;

@@ -487,10 +517,12 @@ DriveInfo *drive_init(QemuOpts *opts, int 
default_to_scsi, int *fatal_error)

     bdrv_flags |= ro ? 0 : BDRV_O_RDWR;

-    ret = bdrv_open(dinfo->bdrv, file, bdrv_flags, drv);
-    if (ret < 0) {
-        fprintf(stderr, "qemu: could not open disk image %s: %s\n",
-                        file, strerror(-ret));
+    dinfo->file = qemu_strdup(file);
+    dinfo->bdrv_flags = bdrv_flags;
+    dinfo->drv = drv;
+    dinfo->opened = 1;
+
+    if (drive_open(dinfo) < 0) {
         goto error;
     }

diff --git a/blockdev.h b/blockdev.h
index 4536b5c..e009fee 100644
--- a/blockdev.h
+++ b/blockdev.h
@@ -29,6 +29,10 @@ struct DriveInfo {
     QemuOpts *opts;
     char serial[BLOCK_SERIAL_STRLEN + 1];
     QTAILQ_ENTRY(DriveInfo) next;
+    int opened;
+    int bdrv_flags;
+    char *file;
+    BlockDriver *drv;
 };

 #define MAX_IDE_DEVS   2
@@ -42,6 +46,8 @@ DriveInfo *drive_get_by_blockdev(BlockDriverState *bs);
 QemuOpts *drive_add(const char *file, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
 DriveInfo *drive_init(QemuOpts *arg, int default_to_scsi, int *fatal_error);

+extern int drives_reinit(void);
+
 /* device-hotplug */

 DriveInfo *add_init_drive(const char *opts);
diff --git a/migration.c b/migration.c
index a8b65e5..fdff804 100644
--- a/migration.c
+++ b/migration.c
@@ -17,6 +17,7 @@
 #include "buffered_file.h"
 #include "sysemu.h"
 #include "block.h"
+#include "blockdev.h"
 #include "qemu_socket.h"
 #include "block-migration.h"
 #include "qemu-objects.h"
@@ -69,6 +70,11 @@ void process_incoming_migration(QEMUFile *f)

     incoming_expected = false;

+    if (drives_reinit() != 0) {
+        fprintf(stderr, "reopening of drives failed\n");
+        exit(1);
+    }
+
     if (autostart)
         vm_start();
 }
-- 
1.7.3.4