OpenBSD::Vstat(3p) Perl Programmers Reference Guide OpenBSD::Vstat(3p)NAMEOpenBSD::Vstat - virtual filesystem for "pkg_add(1)" simulations
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;
DESCRIPTION
"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 "new" expect a $state object, that is, an object with
"$state->{not}" and "$state->errsay" defined.
Operations on the "Vstat" object can modify "$state->{problems}" and
"$state->{overflow}".
The method "add" (respectively "remove") can be used to add a filename
to the file system (resp. remove a filename from the file system). The
method "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 "-e".
Both "add" and "remove" also know about Unix filesystem semantics,
namely mount(8) points and disk usage. They return a small object
corresponding to the filename's file system with the following methods
ro defined if the filesystem is read-only. Usually hard to add
files there.
nodev defined if the filesystem forbids devices.
noexec defined if the filesystem forbids execution.
nosuid defined if the filesystem forbids SUID files.
avail returns the number of bytes still available on the filesystem.
"exists" returns a true value if the filename exists. If it is a
virtual name added through "add", it returns the $tag specified as an
optional argument. Otherwise, it returns 1.
"tally" displays a summary of filesystem manipulations after a series
of additions and removals.
Due to the way packages get updated, size modifications through
"remove" are delayed until the next call to "synchronize": old files
must be removed before adding the new files in order to properly
account for collisions, but the old files occupy disk space while the
new package gets extracted.
Modifications to the virtual file system are stored until a call to
"synchronize", which assumes the real file system will get those
changes (and thus we can forget them), or "drop_changes", which assumes
the changes won't get through, thus providing transactional semantics.
In case of file system overflow, "remove_first" can be used to indicate
file removal happens before the creation of new files.
Typical use is as follows: do lot of changes to the Vstat object
check for overflow. if so, drop_changes. redo the changes,
with remove_first used instead of remove.
In case "$state->{not}" is true, the real file system will never store
changes, and thus the "Vstat" object is layered to allow full
transactional back-out.
BUGS AND LIMITATIONS
"OpenBSD::Vstat" now handles chroot(8) situations gracefully, but it
doesn't know about symbolic links to directories and will report bogus
results in complicated cases.
"OpenBSD::Vstat" needs an interface to deal with removed directories
that get replaced with files. Currently, it will report a conflict.
perl v5.12.2 June 30, 2010