Re: [Qemu-devel] [PATCH 4/7] block: close unused image files at the end of streaming

[Federico Simoncelli]

- Original Message -
 From: Paolo Bonzini pbonz...@redhat.com
 To: qemu-devel@nongnu.org
 Cc: Marcelo Tosatti mtosa...@redhat.com, Federico Simoncelli 
 fsimo...@redhat.com
 Sent: Thursday, April 5, 2012 5:42:58 PM
 Subject: [PATCH 4/7] block: close unused image files at the end of streaming
 
 From: Marcelo Tosatti mtosa...@redhat.com
 
 Close the now unused images that were part of the previous backing
 file
 chain and adjust -backing_hd properly.
 
 Note that this only works with relative paths.

s/relative/absolute/

 Given the images:
 
  /tmp/a/base.raw
  /tmp/a/snap1.qcow2
  /tmp/b/snap2.qcow2
 
 chained as:
 
  base(bak:) - snap1(bak:base.raw) -
  snap2(bak:../a/snap1.qcow2)
 
 merging snap1 and snap2 we will obtain:
 
  base(bak:) - snap2(bak:base.raw)
 
 However this should be maintained by the user/admin: one can also
 screw up relative paths using qemu-img manually.

The patch is fine but I disagree with this comment. The user/admin didn't make
any mistake and he shouldn't be in charge of additional maintenance (which is
also tricky since the VM is running).

-- 
Federico

[Qemu-devel] [PATCH 4/7] block: close unused image files at the end of streaming

[Paolo Bonzini]

From: Marcelo Tosatti mtosa...@redhat.com

Close the now unused images that were part of the previous backing file
chain and adjust -backing_hd properly.

Note that this only works with relative paths.
Given the images:

 /tmp/a/base.raw
 /tmp/a/snap1.qcow2
 /tmp/b/snap2.qcow2

chained as:

 base(bak:) - snap1(bak:base.raw) - snap2(bak:../a/snap1.qcow2)

merging snap1 and snap2 we will obtain:

 base(bak:) - snap2(bak:base.raw)

However this should be maintained by the user/admin: one can also
screw up relative paths using qemu-img manually.

Signed-off-by: Marcelo Tosatti mtosa...@redhat.com
Cc: Federico Simoncelli fsimo...@redhat.com
Signed-off-by: Paolo Bonzini pbonz...@redhat.com
---
 block/stream.c |   23 +++
 1 file changed, 23 insertions(+)

diff --git a/block/stream.c b/block/stream.c
index 61ff7a2..54f2b39 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -76,6 +76,28 @@ static int coroutine_fn stream_populate(BlockDriverState *bs,
 return bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, qiov);
 }
 
+static void close_unused_images(BlockDriverState *top, BlockDriverState *base,
+const char *base_id)
+{
+BlockDriverState *intermediate;
+intermediate = top-backing_hd;
+
+while (intermediate) {
+BlockDriverState *unused;
+
+/* reached base */
+if (intermediate == base) {
+break;
+}
+
+unused = intermediate;
+intermediate = intermediate-backing_hd;
+unused-backing_hd = NULL;
+bdrv_delete(unused);
+}
+top-backing_hd = base;
+}
+
 /*
  * Given an image chain: [BASE] - [INTER1] - [INTER2] - [TOP]
  *
@@ -223,6 +245,7 @@ retry:
 base_id = s-backing_file_id;
 }
 ret = bdrv_change_backing_file(bs, base_id, NULL);
+close_unused_images(bs, base, base_id);
 }
 
 qemu_vfree(buf);
-- 
1.7.9.3