[Qemu-devel] qemu-img:the sheepdog snapshot vdi's lock will not be released when use qemu-img to create a snapshot vdi

[徐小龙 <nxtxiaolong@gmail.com>]

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hi,all,
     when i use `qemu-img snapshot -c test-s sheepdog:test` to create a
snapshot of sheepdog vdi,the snapshot's lock not be released.

root@hty-compute1:~/qemu# ./qemu-img create sheepdog:test 1G
Formatting 'sheepdog:test', fmt=raw size=1073741824

root@hty-compute1:~/qemu# dog vdi list
  Name        Id    Size    Used  Shared    Creation time   VDI id  Copies
 Tag
  test         0  1.0 GB  0.0 MB  0.0 MB 2014-12-22 17:10   7c2b25      3

root@hty-compute1:~/qemu# ./qemu-img snapshot -c test-s sheepdog:test
WARNING: Image format was not specified for 'sheepdog:test' and probing
guessed raw.
         Automatically detecting the format is dangerous for raw images,
write operations on block 0 will be restricted.
         Specify the 'raw' format explicitly to remove the restrictions.

root@hty-compute1:~/qemu# dog vdi lock list
VDI | Owner node | Tag
s test | IPv4 ip:172.16.17.200 port:7000 test-s

when i create a snapshot ,the src vdi will be open and locked,in the
function `sd_open` read the vdi inode info saved in the struct
BDRVSheepdogState ,and in the function `sd_snapshot_create` the vdi inode
information in the struct BDRVSheepdogState will point to an new vdi ,so
when the function `sd_close` be called,the `sd_close` will try to released
the lock of new vdi.In conclusion,the snapshot vdi will lock forever , so
it's will be failed when i try to create a new vdi base on the snapshot.

root@hty-compute1:~/qemu# ./qemu-img create -b sheepdog:test:test-s
sheepdog:new-vdi
qemu-img: sheepdog:new-vdi: cannot get vdi info, VDI is already locked,
test 0 test-s

There may be some wrong in the function`sd_snapshot_create`.but I'm not
sure the root cause.

Thanks,
Xiaolong Xu

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