[Libguestfs] Proposed changes for OpenStack

[Richard W.M. Jones]

On Wed, Dec 14, 2011 at 02:17:05PM +0000, Matthew Booth wrote:
> I still don't see why we need the guestfish event callbacks.

because ...

> >The guestfish change is only for us to do testing.

[...]

> This is an extension of the libguestfs api in a direction which is
> best served by a different tool. I've failed to convince you of this
> argument several times before though, so I'll try a different tack
> ;)
> 
> The reason this isn't going to work is that a FUSE filesystem
> requires a process to exist which can respond to filesystem events
> as they occur. This means that you would have to additionally add
> functions for managing FUSE events, at the very least calling the
> event handler. The API user would have to integrate these calls into
> their event loop. If they didn't have an event loop, they'd have to
> create one. This isn't the simplicity you're looking for.
> 
> Alternatively, they could fork. The problem is, if you do that you
> either need to create a separate appliance (the performance overhead
> you're trying to avoid), or create an interface to an existing
> appliance over which commands from multiple sources can be
> serialised (my suggestion).

I haven't written any code yet so I don't know for certain that it
will work.  With that in mind, the architecture is as follows:

guestfs_mount_local doesn't return until the filesystem is unmounted.

The thread running guestfs_mount_local is the one which is processing
FUSE requests.  In nuts and bolts terms, guestfs_mount_local calls
fuse_main with certain flags to stop it from forking into the
background (or more likely it'll call some of the lower level libfuse
APIs that fuse_main calls).  No event loop integration is needed.

Rich.

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