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$OpenBSD: OpenBSD::Vstat.pod,v 1.5 2010/01/02 14:13:02 espie Exp $
=head1 NAME
OpenBSD::Vstat - virtual filesystem for C<pkg_add(1)> simulations
=head1 SYNOPSIS
use OpenBSD::Vstat;
my $v = OpenBSD::Vstat->new($state);
$h = $v->add($filename, $size, $tag);
$v->remove($filename, $size);
$e = $v->exists($filename);
$v->tally;
=head1 DESCRIPTION
C<OpenBSD::Vstat> provides methods to layout a virtual file system on top
of the real one. This is generally used to simulate file system manipulations
before doing them for real.
The constructor C<new> expect a C<$state> object, that is, an object with
C<$state-E<gt>{not}> and C<$state-E<gt>errsay> defined.
The method C<add> (respectively C<remove>) can be used to add a filename to
the file system (resp. remove a filename from the file system).
The method C<exists> looks for
a given filename: first it checks if it has been added or removed in
the virtual filesystem. Failing that, it looks into the real file system
using C<-e>.
Both C<add> and C<remove> also know about
Unix filesystem semantics, namely C<mount(8)> points and disk usage.
They return a small object corresponding to the filename's file system with
the following methods
=over 8
=item ro
defined if the filesystem is read-only. Usually hard to add files there.
=item nodev
defined if the filesystem forbids devices.
=item noexec
defined if the filesystem forbids execution.
=item nosuid
defined if the filesystem forbids SUID files.
=item avail
returns the number of bytes still available on the filesystem.
=back
C<exists> returns a true value if the filename exists.
If it is a virtual name added through C<add>, it returns
the C<$tag> specified as an optional argument. Otherwise, it returns 1.
C<tally> displays a summary of filesystem manipulations
after a series of additions and removals.
Due to the way packages get updated, size modifications through
C<remove> are delayed until the next call to
C<synchronize>: old files must be removed before
adding the new files in order to properly account for collisions,
but the old files occupy disk space while the new package gets extracted.
=head1 BUGS AND LIMITATIONS
C<OpenBSD::Vstat> now handles C<chroot(8)> situations gracefully, but
it doesn't know about symbolic links to directories and will report bogus
results in complicated cases.
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