Don't write headers if BDS is INACTIVE

Changes from v2->v3:

Patch 2: Uh... fix that misspelling. Thanks Stefan :) Patch 3: New patch to block migration in parallels

git-backport-diff -r qemu/master.. -u 6dc6acb

001/4:[----] [--] 'block/vhdx.c: Don't blindly update the header' 002/4:[----] [--] 'block/parallels: Do not update header or truncate image when INMIGRATE' 003/4:[down] 'block/parallels: add migration blocker'
004/4:[----] [--] 'qemu-iotests: update unsupported image formats in 194'

Changes from v1->v2:

* Drop previous parallels patches, just check BDRV_O_INACTIVE now (Kevin)

git-backport-diff -r qemu/master.. -u github/master
Key:
[----] : patches are identical
[####] : number of functional differences between upstream/downstream patch [down] : patch is downstream-only
The flags [FC] indicate (F)unctional and (C)ontextual differences, respectively

001/3:[----] [--] 'block/vhdx.c: Don't blindly update the header' 002/3:[down] 'block/parallals: Do not update header or truncate image when INMIGRATE' 003/3:[----] [--] 'qemu-iotests: update unsupported image formats in 194'

v1:

VHDX and Parallels both blindly write headers to the image file if the images are opened R/W. This causes an assert if the QEMU run state is INMIGRATE.

Jeff Cody (4):
block/vhdx.c: Don't blindly update the header block/parallels: Do not update header or truncate image when INMIGRATE block/parallels: add migration blocker
qemu-iotests: update unsupported image formats in 194

 block/parallels.c      | 19 ++++++++++++++-----
 block/vhdx.c           |  7 -------
 tests/qemu-iotests/194 |  2 +-
 3 files changed, 15 insertions(+), 13 deletions(-)

2.9.5

The VHDX specification requires that before user data modification of the vhdx image, the VHDX header file and data GUIDs need to be updated. In vhdx_open(), if the image is set to RDWR, we go ahead and update the header.

However, just because the image is set to RDWR does not mean we can go ahead and write at this point - specifically, if the QEMU run state is INMIGRATE, the underlying file BS may be set to inactive via the BDS open flag of BDRV_O_INACTIVE. Attempting to write under this condition will cause an assert in bdrv_co_pwritev().

We can alternatively latch the first time the image is written. And lo and behold, we do just that, via vhdx_user_visible_write() in vhdx_co_writev(). This means the call to vhdx_update_headers() in vhdx_open() is likely just vestigial, and can be removed.

---
 block/vhdx.c | 7 -------
 1 file changed, 7 deletions(-)

index 7ae4589..9956933 100644
@@ -1008,13 +1008,6 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    if (flags & BDRV_O_RDWR) {
-        ret = vhdx_update_headers(bs, s, false, NULL);
-        if (ret < 0) {
-            goto fail;
-        }
-    }
-
     /* TODO: differencing files */
 
     return 0;

2.9.5

If we write or modify the image file while the QEMU run state is INMIGRATE, then the BDRV_O_INACTIVE BDS flag is set. This will cause an assert, since the image is marked inactive. Make sure we obey this flag.

---
 block/parallels.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

index 2b6c6e5..7b7a3ef 100644
@@ -708,7 +708,7 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
         s->prealloc_mode = PRL_PREALLOC_MODE_FALLOCATE;
     }
 
-    if (flags & BDRV_O_RDWR) {
+    if ((flags & BDRV_O_RDWR) && !(flags & BDRV_O_INACTIVE)) {
         s->header->inuse = cpu_to_le32(HEADER_INUSE_MAGIC);
         ret = parallels_update_header(bs);
         if (ret < 0) {

@@ -741,12 +741,9 @@ static void parallels_close(BlockDriverState *bs)
 {
     BDRVParallelsState *s = bs->opaque;
 
-    if (bs->open_flags & BDRV_O_RDWR) {
+    if ((bs->open_flags & BDRV_O_RDWR) && !(bs->open_flags & BDRV_O_INACTIVE)) {
         s->header->inuse = 0;
         parallels_update_header(bs);
-    }
-
-    if (bs->open_flags & BDRV_O_RDWR) {
         bdrv_truncate(bs->file, s->data_end << BDRV_SECTOR_BITS,
                       PREALLOC_MODE_OFF, NULL);
     }

2.9.5

Migration does not work for parallels, and has been broken for a while (see patch 'block/parallels: Do not update header or truncate image when
INMIGRATE'). The bdrv_invalidate_cache() method needs to be added for
migration to be supported. Until this is done, prohibit migration.

---
 block/parallels.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

index 7b7a3ef..ffe0a79 100644
@@ -35,6 +35,7 @@
 #include "qemu/module.h"
 #include "qemu/bswap.h"
 #include "qemu/bitmap.h"
+#include "migration/blocker.h"
 
 /**************************************************************/
 

@@ -100,6 +101,7 @@ typedef struct BDRVParallelsState {
     unsigned int tracks;
 
     unsigned int off_multiplier;
+    Error *migration_blocker;
 } BDRVParallelsState;
 
 

@@ -720,6 +722,16 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
     s->bat_dirty_bmap =
         bitmap_new(DIV_ROUND_UP(s->header_size, s->bat_dirty_block));
 
+    /* Disable migration until bdrv_invalidate_cache method is added */
+    error_setg(&s->migration_blocker, "The Parallels format used by node '%s' "
+               "does not support live migration",
+               bdrv_get_device_or_node_name(bs));
+    ret = migrate_add_blocker(s->migration_blocker, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        error_free(s->migration_blocker);
+        goto fail;
+    }
     qemu_co_mutex_init(&s->lock);
     return 0;
 

2.9.5

Test 194 checks for 'luks' to exclude as an unsupported format, However, most formats are unsupported, due to migration blockers.

Rather than specifying a blacklist of unsupported formats, whitelist supported formats (specifically, qcow2, qed, raw, dmg).

---
 tests/qemu-iotests/194 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 8d973b4..1d4214a 100755
@@ -21,7 +21,7 @@
 
 import iotests
 
-iotests.verify_image_format(unsupported_fmts=['luks'])
+iotests.verify_image_format(supported_fmts=['qcow2', 'qed', 'raw', 'dmg'])
 iotests.verify_platform(['linux'])
 
 with iotests.FilePath('source.img') as source_img_path, \

2.9.5