Fixes Incorrect documentation docker volume create - Issue #47606

[Anish-M]

fixes #47606
- What I did
I changed the adapter.go file to throw an error if a container with the name already exists

- How I did it
I get the volume based on the name, and if the volume is returned (i.e. err is null) it means that a volume of the given name exists. Since err is null, this means such a volume exists, which means an error and corresponding error message according to the docker documentation outlined in the issue is thrown.

- How to verify it

Run the docker volume create [NAME] and use the name of an already existing volume.

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

Signed-off-by: Anish Mankal anish.mankal@gmail.com

[thaJeztah]

Hm.. I don't think this change is correct, but the documentation may need a more complete example; https://docs.docker.com/reference/cli/docker/volume/create/

The important part here is that the name must be unique across drivers, so no 2 volumes should be allowed with the same name across multiple drivers, but for the same driver, it's treated as an idempotent action;

If you specify a volume name already in use on the current driver, Docker assumes you want to re-use the existing volume and doesn't return an error.

I once opened a ticket to suggest it should always be an error, but that ship likely sailed, and may be too late now to change that behavior;

• Docker volume create should not be idempotent (by default) #16068

[Anish-M]

I see, if its decided upon not to always raise an error, I changed it to only raise the error if it's not the same driver name; if it is the same driver, let the current behavior continue. Is this an acceptable implementation?

[thaJeztah]

I wonder if this is already handled; looking at

moby/volume/service/store.go

Lines 511 to 524 in 8e14f27

	// checkConflict checks the local cache for name collisions with the passed in name,
	// for existing volumes with the same name but in a different driver.
	// This is used by `Create` as a best effort to prevent name collisions for volumes.
	// If a matching volume is found that is not a conflict that is returned so the caller
	// does not need to perform an additional lookup.
	// When no matching volume is found, both returns will be nil
	//
	// Note: This does not probe all the drivers for name collisions because v1 plugins
	// are very slow, particularly if the plugin is down, and cause other issues,
	// particularly around locking the store.
	// TODO(cpuguy83): With v2 plugins this shouldn't be a problem. Could also potentially
	// use a connect timeout for this kind of check to ensure we aren't blocking for a
	// long time.
	func (s *VolumeStore) checkConflict(ctx context.Context, name, driverName string) (volume.Volume, error) {

And, more specifically, these lines

moby/volume/service/store.go

Lines 553 to 558 in 8e14f27

	if exists {
	if conflict {
	return nil, errors.Wrapf(errNameConflict, "driver '%s' already has volume '%s'", vDriverName, name)
	}
	return v, nil
	}