Public methods implementation

• $\texttt{PkgDebian()}$: the constructor configures the object pointed by $\texttt{*\_config}$ through the functions $\texttt{pkgInitConfig()}$ and $\texttt{pkgInitSystem()}$. They must be invoked before calling many APT library functions. Both these functions are defined in $\texttt{<apt-pkg/init.h>}$;
• $\texttt{string CachePath()}$: it returns the pathname of the APT packages cache;
• $\texttt{int getInfo(void *}$pkgPtr, $\texttt{string \&}$buffer $\texttt{)}$: it fills the buffer with the metadata of the package identified by pkgPtr. Currently they are: name, version, section, priority, dependencies, packages provided, description, maintainer and filename in the pool of packages repository. We described how to get most of them in the $\texttt{PkgIterator}$ class description;
• $\texttt{int getDepends(void *}$pkgPtr, $\texttt{string \&}$buffer $\texttt{)}$ and
  $\texttt{int getRDepends(void *}$pkgPtr, $\texttt{string \&}$buffer $\texttt{)}$: these methods
  mainly use a $\texttt{DepIterator}$ instance. As we have shown in section 5.3.4.2, this kind of object can iterate over lists of version dependencies and package reverse dependencies. Thus, the only difference between them consists in the set of data being iterated. If we consider $\texttt{Pkg}$ a $\texttt{PkgIterator}$ instance, the version dependencies are iterated by
  $\texttt{Pkg.VersionList().DependsList()}$, the package reverse dependencies by $\texttt{Pkg.RevDependsList()}$;
• $\texttt{int getOwnedFiles(string }$pkg_name, $\texttt{string \&}$buffer $\texttt{)}$: it fills the buffer with the names of the files owned by the package pkg_name. It slightly differs from the other functions since the package is not identified by the cache entry pointer, but by its name. This is due to the Debian particular way in managing owned files. They are
  stored in the files $\texttt{/var/lib/dpkg/info/}$pkg_name $\texttt{.list}$ and
  $\texttt{/var/lib/dpkg/info/}$pkg_name $\texttt{.conffiles}$. Caching of $\texttt{info/*}$ files content will be the next step in APT development[Gun03]. Although this facility is not supported, it does not represent a big problem to PackageFS, since in the next version our implementation will provide overloading functions for some PkgManager methods. They will be useful for other package managers;
• $\texttt{int install(string}$ pkg_name, $\texttt{string}$ options $\texttt{)}$ and
  $\texttt{int remove(string}$ pkg_name, $\texttt{string}$ options $\texttt{)}$: these methods call respectively the command apt-get install and apt-get remove.
  By default the -qq option is given to make APT silent and ever assuming positive answers. The other associated options are retrieved by $\texttt{*\_config}$ methods. While a package is being installed, it is pre-configured by debconf, which arises the interactivity problem: we repeat here that the daemon process has to raise neither input, nor output requests through its standard communication channels. Thus we check for the $\texttt{DISPLAY}$ environment value, so that we set the $\texttt{DEBIAN\_FRONTEND}$ variable to make debconf using the appropriate frontend. If the debconf graphical interface can be run, the administrator is able to set the configuration options, since he is asked for them in a separate window. If $\texttt{DISPLAY}$ is not set, the debconf frontend becomes non-interactive and the administrator has to subsequently run the configuration procedure by himself (i.e. with the command $\texttt{dpkg-reconfigure}$ pkg_name);
• $\texttt{int update()}$ : it runs apt-get update;
• $\texttt{int upgrade()}$ : it runs apt-get upgrade.