[linux-lvm] lvm filter regex format

[linux-lvm] lvm filter regex format

[Thanos Makatos]

I'm trying to be very specific in the global_filter of lvm.conf and
ignore devices under /dev/mapper of the format
'^/dev/mapper/[a-z0-9]{14}$', however the repetition count '{14}' does
not seem to be honored?

Currently I have to repeat '[a-z0-9]' fourteen times, which works but
it's a bit ugly.

Does the filter use some standarized regex format?

-- 
Thanos Makatos

Re: [linux-lvm] lvm filter regex format

[Joe Thornber]

On Mon, Dec 18, 2017 at 05:16:14PM +0000, Thanos Makatos wrote:
> I'm trying to be very specific in the global_filter of lvm.conf and
> ignore devices under /dev/mapper of the format
> '^/dev/mapper/[a-z0-9]{14}$', however the repetition count '{14}' does
> not seem to be honored?
> 
> Currently I have to repeat '[a-z0-9]' fourteen times, which works but
> it's a bit ugly.
> 
> Does the filter use some standarized regex format?

It's a custom engine that I wrote which matches all the regexs in the
filters at the same time (so is pretty fast).  Looking at the header here:

   https://github.com/jthornber/lvm2-ejt/blob/master/libdm/regex/parse_rx.h

It seems to support just catenation, |, *, +, ?, [<charset>], ^ and $

Out of interest why are you using the length of the device name as a discriminator?

- Joe

Re: [linux-lvm] lvm filter regex format

[Thanos Makatos]

> Out of interest why are you using the length of the device name as a discriminator?

In my case I am the one who creates these devices so I fully control
the naming scheme, however there are other components in our product
that might create device mapper targets and I shouldn't filter them
out.

Re: [linux-lvm] lvm filter regex format

[Joe Thornber]

On Mon, Dec 18, 2017 at 06:53:06PM +0000, matthew patton wrote:
> > �  https://github.com/jthornber/lvm2-ejt/blob/master/libdm/regex/parse_rx.h
>  
> not to be ungrateful but why on earth would one NOT use the glibc standard regex library? Nobody cares about pointless optimization. Surprises like "well, we only implemented most of the spec" are what drives people nuts!

It was written about 17 years ago, and the optimisation was not pointless at that time.

- Joe

Re: [linux-lvm] lvm filter regex format

[Zdenek Kabelac]

Dne 18.12.2017 v 19:53 matthew patton napsal(a):
>>     https://github.com/jthornber/lvm2-ejt/blob/master/libdm/regex/parse_rx.h
>   
> not to be ungrateful but why on earth would one NOT use the glibc standard regex library? Nobody cares about pointless optimization. Surprises like "well, we only implemented most of the spec" are what drives people nuts!
> 
> I agree this particular length-based match is rather odd but there are plenty of useful examples I am sure that could benefit from {x,y} notation.


Such code was actually written long time ago - but since the syntax of 
standard glibc  regex accepts slightly different strings - it would be an 
incompatible change - so it's been considered now worth breaking the 
compatibility at that time...


Regards

Zdenek

Re: [linux-lvm] lvm filter regex format

[matthew patton]

>    https://github.com/jthornber/lvm2-ejt/blob/master/libdm/regex/parse_rx.h
 
not to be ungrateful but why on earth would one NOT use the glibc standard regex library? Nobody cares about pointless optimization. Surprises like "well, we only implemented most of the spec" are what drives people nuts!

I agree this particular length-based match is rather odd but there are plenty of useful examples I am sure that could benefit from {x,y} notation.