Re: [Bacula-devel] New project : relocate files and directories when restoring

[Kern S. <ke...@si...>]

On Friday 02 March 2007 10:52, BOLLENGIER Eric wrote:
> Hi,
>
> > first, the idea is a good one and would allow important things to
> > happen. One example you missed: backing up from a linux LVM snapshot
> > (where the snapshot for /home might be in /.snapshot/home) and restoring
> > to the right originallocation (/home in this example).
> >
> > >           When i use Linux or SAN snapshot, i mount them to
> > > /mnt/snap_xxx so, when a restore a file, i have to move by hand
> > >           from /mnt/snap_xxx/file to /xxx/file. I can't replace a file
> > >           easily.
> > >
> > >
> > >
> > >   Notes:  I think we can enhance the where= option very easily by
> > >           allowing regexp expression. (by replacing bregex by libpcre
> > >           see http://en.wikipedia.org/wiki/PCRE and
> > > http://www.pcre.org/)
> > >
> > >           Since, many users think that regexp are not user friendly,
> >
> > I don't know much about many users, but I do know that I at the same
> > time like REs for their power, but hate them for all the thinking and
> > trying I have to invest before they work.
>
> It's ok, but regexp is a common language, you find them with :
>  - shell (with sed)
>  - perl
>  - python
>  - php
>  - java
>  - bacula (in fileset)
>  - vi, emacs
>  - Exim, postfix
>  - Apache
>  - etc.
>
> If you do not know them, I advise you to throw a glance, it is a tool very
> much used and very powerful.
>
> > >           i think
> > >           that bat, bconsole or brestore must provide a simple way to
> > >           configure where= option (i think to something like in
> > >           openoffice "search and replace").
> > >
> > >           Ie, if user uses where=/tmp/bacula-restore, we keep the old
> > >           fashion.
> >
> > The above - sure thing.
> > Your below suggestions - not so sure. I don't especially like the syntax
> > you suggest, and I don't think it is very user-friendly.
> >
> > A GUI could spare the user any contact with the textual representation
> > of the where= clause.
>
> I think that bat can have 2 fields like
> Replace =
> With =
>
> and bat will send the good where= to director
>
> > For input, I thought about something where you can use special path
> > elements.
> >
> > the idea: A path consists of a number of elements, separated by path
> > delimiters (/ in unix, \ in windows, always a forward slash in Bacula).
>
> I don't agree with you, you want to rewrite a new langage just for bacula
> restoration ? Sure, you will have to invest before they work.
>
> It will need lots of new code, instead of using a common
> library.
>
> > So, you can disassemble any path into a number of path elements.
> >
> > There are not many characters that can be used to mark a path element
> > descriptor in Bacula, so we need something that is both readily
> > available on all or most keyboard layouts and seldomly used in path
> > names.
> >
> > Several characters to mark path elements would be available:
> > \   good choice, because it's commonly used as an escape character.
> >      bad chioce because windows users will make more mistakes than
> >      necessary
> > #   possibly usable
> > {}  possibly usable.
> >
> > I prefer the braces because I imagine we will need to group things
> > together, which suggests some sort of parentheses.
> >
> > The syntax I imagine could be somehing like this:
> > - Take a path as given in the where clause.
> > - normal path elements remain unchanged, i.e. /home/arno remains
> > /home/arno - a path element can be a simple number, where the number
> > represents the path element number from the beginning, counting with 1.
> > Take this original path for the examples:
> >
> > /var/spool/imap/user/its-al/Mailinglists/bacula-devel/
> >
> > If I wrote /tmp/{7}/ I would refer to the directory /tmp/bacula-devel.
>
> where=/tmp/{7}/ instead of
>
> where=s!/var/spool/imap/user/its-al/Mailinglists!/tmp!
> or
> where=s!.*bacula-devel!/tmp/bacula-devel!
>
> I don't think it's more easy to read (and to write).
>
> And in bacula it's more simple and less buggy to check the first char to
> know it bacula must use regexp.

I want to hear more about regex vs some other proposal (i.e. I'm still open on 
this subject), but unfortunately, Eric, s is a perfectly legal first 
character for a where, so assuming we did regexes, which are very powerfull, 
but not very user friendly, we need another mechanism to distinguish it from 
a path specification -- it will probably be necessary to add something like a 
regexwhere command, in which case, I don't think the s will even be needed.


>
> > A negative number would indicate to take the elements from the end of
> > the path elements list, so /{-1}/ would refer to the direcetory
> > /bacula-devel.
> > Non-existing path elements would be the empty string, so /tmp/{5}/{12}
> > would refer to /tmp/its-al, just like /tmp/{5}/{-18} would.
> >
> > Note that you could also use a clause like
> > /tmp/{5}_{7} which would refer to a path /tmp/its-al_bacula-devel
> >
> > The {0} should refer to the whole, original path.
> > - A path element could also be a special operation. The following
> > operations look reasonable:
> > * drop an element
> > * replace an element
> > * modify an element
> > Such an operation could be noted in the path element reference as
> > introduced, or could be written separately.
> > I use the following operation designators:
> > ! drop an element
> > = replace an element (simple form suitable to people without RE
> > experience) s///-syntax as known from pcre, sed, or whatever can be
> > implemented for more sophisticated use.
> >
> > You could write things like
> > /{2!}{0} which would drop path element 2 and keep all others unchanged,
> > creating /var/imap/user/its-al/Mailinglists/bacula-devel/ as a path.
> >
> > This syntax would be perfect for LVM snapshot backups: you backup from
> > /.snapshot/home and restore to /{1!}{0}.
>
> where=/{1!}{0} instead of where=s!/.snapshot!!       (or
> where=s/.snapshot//)
>
> which is a very common thing for unix user
>
> (with regexp, you can choose your separator s/toto/titi/ is like
> s!toto!titi!, it's more path friendly)
>
> > Replacing a path element would look like this: /{1=/restore}{0} which
> > would restore a backup taken from /.snapshot/home to /restore/home.
> >
> > (I'll leave the s///-syntax to your imagination; I don't want to wrap my
> > mind around REs now)
> >
> > Finally, you could do things like a restore to
> > {3!}{4!}{5!}{6!}{7!}{8!}{9!}/tmp/{1}/{2=oldspool}/which would really mix
> > up all my mail, but we do need an option for the users to really need
> > our support :-)
> >
> > - finally, we need a way to attach a suffix or prefix to the file name
> > (I don't think more modifications are useful; that would make it too
> > hard to understand which file was what). I'd use the special operations
> > + and - for that, plus for a suffix, minus for a prefix.
>
> Stop please, my brain will explode :)
>
> > So, for my mail, you could restore to {+-old}{0} which would add "-old"
> > to the file name restored to the original location, or {-old-}{0} which
> > would prefix "old-" to the mail files.
> >
> > >           If user uses something like where=s!/prod!/test!, files will
> > >           be restored from /prod/xxx to /test/xxx.
> > >
> > >           If user uses something like where=s/$/.old/, files will
> > >           be restored from /prod/xxx.txt to /prod/xxx.txt.old.
> > >
> > >           If user uses something like where=s/txt$/old.txt/, files will
> > >           be restored from /prod/xxx.txt to /prod/xxx.old.txt
> > >
> > >           if user uses something like where=s/([a-z]+)$/old.$1/, files
> > > will be restored from /prod/xxx.ext to /prod/xxx.old.ext
> > >
> > >
> > > Nice, isn't it ?
> >
> > Nah, I don't like your syntax suggestions :-)
>
> Me too :)
>
> > But apart from that - yes.
> >
> > (Oh, and I've been thinking about something similar, of course... I
> > didn't invent all that stuff above in a few minutes. Which doesn't mean
> > there can't be misconceptions in there that others note in a minute ;-)
> >
> > Arno
>
> Thanks for your feedback
>
> Bye
>
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