Upgrades and image manifests

[Alexander Larsson]

On Fri, 2007-06-29 at 08:22 -0400, Dan Williams wrote:
> Two questions here:
> 
> 1) what does the scheme do in the case where the file it's about to
> replace on the local machine isn't the same as what the manifest on the
> local machine says?  ie, local changes have changed the sha1 hash of the
> local file.  That's essentially a policy decision, do we replace when
> there are local changes or don't we.  A %config-type thing could work
> here to mark files that you may/may not always want to replace.

At the moment it only touches the files that are affected by the diff in
the manifest. If a file wasn't changed in the manifests we don't even
look at it. However, if the file we're replacing has changed locally, we
currently throw that away.

> 2) After downloading a blob, I assume the tool sha1s the downloaded file
> to ensure that it's content matches the name, right?

Yeah, or rather, while downloading.

> > We need a library to do http downloads. I see we're shipping libcurl on
> > the laptop. Is it ok to use this library? 
> 
> Yeah, though the ironic thing just occurred to me that libcurl is (along
> with Mozilla) one of the more frequently updated pieces of a linux
> distro :)

I ended up using urllib2 in python.

> > (We also need a very simple http sever that maps sha1 -> file in system
> > image for laptop-to-laptop upgrades, but I think we can do that without
> > using a library.)
> 
> "simple" means lighttpd in my mind, but apache has a longer track
> record.

simple means 300 lines of C code in serve-manifest.c...