Re: [PATCH] xl: Check for dependencies in xl

[Ian Campbell <Ian.Campbell@eu.citrix.com>]

On Fri, 2011-01-14 at 18:57 +0000, Kamala Narasimhan wrote:
> 
> > The next thing after this xtl_createlogger_stdiostream(...) is a
> call to
> > libxl_ctx_init which will try and open the xenstore in the same way
> and
> > has error logging already so perhaps we should improve on that
> instead
> > of adding a separate check?
> >
> >
> 
> Aren't we making the following assumptions in doing so -
> 
> 1)  xtl_createlogger_stdiostream would always be the first function
> called that uses xenstore.

You mean "libxl_ctx_init would always be..."?

In that case yes since that it is the function contains opens the
connection to xenstore so it must be called first. A libxl user
shouldn't need to see or use xenstore directly itself since libxl
encapsulates this.

xtl_createlogger_stdiostream does/can not use xenstore since it comes
from libxc which is beneath (or perhaps alongside) libxenstore in the
software stack.

> 2)  There aren't likely to be other dependency checks to be added in
> future that might warrant a separate function to perform such checks? 

It's not clear what other checks there will end up being but those which
are due to libxl's dependencies (e.g. xenstore) should be in a libxl
function. This could be a separate libxl_check_dependencies() but I
can't see any reason not to do it in libxl_ctx_init().

If xl has some dependency of its own independent of libxl which it is
useful to check then it would be appropriate to add those checks to xl
itself.

Ian.