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Re: [Qemu-devel] [PATCH v20 13/30] block: new bdrv_reopen_bitmaps_rw int


From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-devel] [PATCH v20 13/30] block: new bdrv_reopen_bitmaps_rw interface
Date: Tue, 13 Jun 2017 13:25:13 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1

09.06.2017 16:27, Max Reitz wrote:
On 2017-06-02 13:21, Vladimir Sementsov-Ogievskiy wrote:
Add format driver handler, which should mark loaded read-only
bitmaps as 'IN_USE' in the image and unset read_only field in
corresponding BdrvDirtyBitmap's.

Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
  block.c                   | 17 +++++++++++++++++
  include/block/block_int.h |  7 +++++++
  2 files changed, 24 insertions(+)

diff --git a/block.c b/block.c
index 04af7697dc..161db9e32a 100644
--- a/block.c
+++ b/block.c
@@ -2946,12 +2946,16 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
  {
      BlockDriver *drv;
      BlockDriverState *bs;
+    bool old_can_write, new_can_write;
assert(reopen_state != NULL);
      bs = reopen_state->bs;
      drv = bs->drv;
      assert(drv != NULL);
+ old_can_write =
+        !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) & BDRV_O_INACTIVE);
+
      /* If there are any driver level actions to take */
      if (drv->bdrv_reopen_commit) {
          drv->bdrv_reopen_commit(reopen_state);
@@ -2965,6 +2969,19 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
      bs->read_only = !(reopen_state->flags & BDRV_O_RDWR);
bdrv_refresh_limits(bs, NULL);
+
+    new_can_write =
+        !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) & BDRV_O_INACTIVE);
+    if (!old_can_write && new_can_write && drv->bdrv_reopen_bitmaps_rw) {
+        Error *local_err = NULL;
+        if (drv->bdrv_reopen_bitmaps_rw(bs, &local_err) < 0) {
+            /* This is not fatal, bitmaps just left read-only, so all following
+             * writes will fail. User can remove read-only bitmaps to unblock
+             * writes.
+             */
In a sense, it pretty much is fatal. We were asked to make the image
non-read-only but we failed because it effectively still is read-only.

But I can't think of anything better, and you're right, removing the
bitmaps would resolve the situation. This would require the user to know
that updating the bitmaps was the issue, and local_err may not actually
reflect that.

+            error_report_err(local_err);
So I'd prepend this with something like "$node_name: Failed to make
dirty bitmaps writable", and maybe append a hint like "Removing all
persistent dirty bitmaps from this node will allow writing to it".

Ok for prepending, but I don't want to add last note, as for the user it may better to retry an operation, leading reopening image rw..


Max

+        }
+    }
  }
/*
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 8d3724cce6..1dc6f2e90d 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -380,6 +380,13 @@ struct BlockDriver {
                               uint64_t parent_perm, uint64_t parent_shared,
                               uint64_t *nperm, uint64_t *nshared);
+ /**
+     * Bitmaps should be marked as 'IN_USE' in the image on reopening image
+     * as rw. This handler should realize it. It also should unset readonly
+     * field of BlockDirtyBitmap's in case of success.
+     */
+    int (*bdrv_reopen_bitmaps_rw)(BlockDriverState *bs, Error **errp);
+
      QLIST_ENTRY(BlockDriver) list;
  };


--
Best regards,
Vladimir




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