pkgCacheFile

$\texttt{pkgCacheFile}$ is a wrapper class for opening, generating and closing the cache. It is the main actor of the ``cache operations'' category. $\texttt{pkgCacheFile}$ implements a simple mechanism to open various sorts of caches. It can operate as root, as non-root, show progress and so on, it transparently handles everything is necessary. This means it can rebuild caches from the source list and instantiates and prepares the standard policy mechanism. It is defined in the header file $\texttt{<apt-pkg/cachefile.h>}$. The methods we use are:

• $\texttt{bool Open(OpProgress \&}$Progress, $\texttt{bool}$ Withlock $\texttt{= true)}$: it is used to open the packages cache. The first input parameter is a progress indicator that, in our case, it set not to display ouput (to hide the typical ``Reading Package Lists...'' and ``Building Dependency Tree...''). The second one is a lock flag that is true by default. Since PackageFS opens the cache only for reading purposes, no lock is needed. This function is called into the $\texttt{PkgDebian::readCache()}$ method;
• $\texttt{void Close()}$: it simply closes the cache;
• $\texttt{PkgIterator PkgBegin()}$: it initializes an iterator to the first cache entry;
• $\texttt{PkgIterator FindPkg(string}$ Name $\texttt{)}$: this method belongs to the $\texttt{pkgCache}$ class which is defined in $\texttt{<apt-pkg/pkgcache.h>}$. The developer can transparently access it through the $\texttt{pkgCacheFile}$ class. As the reader can imagine, this method is used inside $\texttt{PkgDebian::findPkg()}$ to reach a particular package entry.