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Add transaction to containerd #3
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ping @milindchawre I have submit this PR here , please have a look? |
Why we need transaction in containerd: When docker send grpc messages to containerd, it always forward to exec runc to do something. And then send back a event to docker. But if the containerd was killed or crashed after receving grpc message, before sending back the events. These is no way to recover it. This may cause the data of container not the same between docker and containerd. How to implement: We add a transaction mechanism: * Open a transaction: This will return a Transaction interface ``` transaction,err := transactionFactory.OpenTransaction(containerID, transactionType, otherMetada) ``` * Close the transaction: ``` transaction.Close() ``` Signed-off-by: Wentao Zhang <zhangwentao234@huawei.com>
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(below is a quote from my runc commit 6f82d4b)
TL;DR: check for IsExist(err) after a failed MkdirAll() is both
redundant and wrong -- so two reasons to remove it.
Quoting MkdirAll documentation:
> MkdirAll creates a directory named path, along with any necessary
> parents, and returns nil, or else returns an error. If path
> is already a directory, MkdirAll does nothing and returns nil.
This means two things:
1. If a directory to be created already exists, no error is
returned.
2. If the error returned is IsExist (EEXIST), it means there exists
a non-directory with the same name as MkdirAll need to use for
directory. Example: we want to MkdirAll("a/b"), but file "a"
(or "a/b") already exists, so MkdirAll fails.
The above is a theory, based on quoted documentation and my UNIX
knowledge.
3. In practice, though, current MkdirAll implementation [1] returns
ENOTDIR in most of cases described in docker-archive#2, with the exception when
there is a race between MkdirAll and someone else creating the
last component of MkdirAll argument as a file. In this very case
MkdirAll() will indeed return EEXIST.
Because of docker-archive#1, IsExist check after MkdirAll is not needed.
Because of docker-archive#2 and docker-archive#3, ignoring IsExist error is just plain wrong,
as directory we require is not created. It's cleaner to report
the error now.
Note this error is all over the tree, I guess due to copy-paste,
or trying to follow the same usage pattern as for Mkdir(),
or some not quite correct examples on the Internet.
[1] https://github.com/golang/go/blob/f9ed2f75/src/os/path.go
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Why we need transaction in containerd:
When docker send grpc messages to containerd, it always forward to exec runc to do something.
And then send back a event to docker.
But if the containerd was killed or crashed after receving grpc message, before sending back the events.
These is no way to recover it. This may cause the data of container not the same between docker and containerd.
How to implement:
We add a transaction mechanism:
This will return a Transaction interface, When we open a transaction, will write the transaction data into disk by sync mode.
when the event was sent to docker, the transaction will be closed (removing from disk and memory).
Signed-off-by: Wentao Zhang zhangwentao234@huawei.com