[Devel] Re: [BUG][cryo] Create file on restart ?

[Matt Helsley]

On Wed, 2008-07-16 at 14:26 -0700, sukadev at us.ibm.com wrote:
> Serge E. Hallyn [serue at us.ibm.com] wrote:
> | Quoting sukadev at us.ibm.com (sukadev at us.ibm.com):
> | > Serge E. Hallyn [serue at us.ibm.com] wrote:
> | > | Quoting sukadev at us.ibm.com (sukadev at us.ibm.com):
> | > | > 
> | > | > cryo does not (cannot ?) recreate files if the application created
> | > | 
> | > | I think that's for the best.
> | > | 
> | > | Don't you?
> | > 
> | > I can understand that configuration or data files should exist, but
> | > not sure about temporary or log files that an application created
> | > upon start-up and expects to be present. Should the admin find
> | > out about them and create them by hand before restart ?
> | 
> | I think the admin should have set the destination environment such that
> | the task is restarted in the same network fs in the same directory, with
> | no files having been deleted.

[Assuming Serge meant: s/network fs/network, fs,/]

> or new files created ? For instance if the application was checkpointed
> before it created a temporary file with O_EXCL flag, that temporary
> file must not exist when restarting ?

	I think that's not a problem given my assumptions above. The filesystem
that the application restarts in would be the same because the admin
should have set up the restart environment as Serge suggested. The admin
can't rely on restart in an alternate environment. However, given
knowledge of the application and environment, using an alternate
environment may be a risk the admin is willing to take.

> | 
> | Am I wrong?
> 
> So we take a snapshot of the FS and checkpoint the application. Do they
> need to be atomic ?

	If all the applications in a container are frozen then I think we can
get fs snapshots consistent with checkpointed applications.
Otherwise, yes, I think we'd be gambling that the checkpointed
application isn't interacting with another, running, application via an
intermittently-shared file.

Cheers,
	-Matt

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