[rtems-users] Re: tar filesystem

[Joel Sherrill <joel@OARcorp.com>]

Till Straumann wrote:
> Joel Sherrill wrote:
> 
>>  Till Straumann wrote:
>>
>> > D. Peter Siddons wrote:
>> >
>> >> It has been on my to-do list to use this feature for some time,
>> >> for a similar application to Eric's. Since the calls are
>> >> documented in the manuals I had assumed they existed! Naive, I
>> >> suppose... Pete.
>> >
>> >
>> >
>> >
>> > I am using rtems_tarfs_load() in my GeSys application
>> > (RTEMS-4.6.2/psim) and it works fine... It also builds without
>> > hacking.
>>
>>
>>  It was accidentally dropped from a Makefile.am in the post 4.6
>>  Makefile.am reduction. Just unlucky that no one noticed it.
>>
>>  Just to repeat.. libmisc/untar loads a tar image generically into a
>>  filesystem of any type and should be portable. It forces the
>>  filesystem to create new fiels and storage for them.
>>
>>  The IMFS load tar code is similar and from the same author if I
>>  recall correctly. But it has a critical difference -- it leaves the
>>  file contents in Flash/ROM and only allocates the IMFS control
>>  information from RAM. So you an 90+% of the benefit of a true ROM
>>  filesystem with a fraction of the code of a new filesystem.
> 
> 
> Nice, indeed -- there's a caveat, however: if the file in the tarball has
> user write permission it is actually copied into RAM. So make sure to
> turn write permissions off if you want the data to reside in ROM.

Eric Norum suggested offline that the copy could be deferred until
this type of file (linear) was opened for writing or truncated.
This would require making a subroutine to convert linear memfile to
a regular memfile and calling it from the IMFS open() and truncate()
handlers.

Probably on the low end of the difficulty scale.
--joel

> -- Till
> 
>>  Plus you
>>  use tar to create the ROM image -- not some new host tool which we
>>  would have to develop and keep in sync.
>>
>>  --joel
>>
>> > -- Till
>> >
>> >
>> >>
>> >>
>> >> Ralf Corsepius wrote:
>> >>
>> >>> On Fri, 2005-02-04 at 13:41 -0600, Joel Sherrill wrote:
>> >>>
>> >>>
>> >>>> FYI .. this was sent to rtems-users at OARcorp.com not
>> >>>> rtems.com. They are separate domains and machines now. :)
>> >>>>
>> >>>> Eric Norum wrote:
>> >>>>
>> >>>>
>> >>>>> Why is cpukit/libfs/src/imfs/imfs_load_tar.c no longer
>> >>>>> being built? It looks like just the thing I need for my
>> >>>>> standalone EPICS IOC.
>> >>>>>
>> >>>>
>> >>>> My guess is probably just an accidental oversight in some
>> >>>> Makefile.am updates.
>> >>>>
>> >>>
>> >>> Probably, I don't know. Digging CVS-history shows it had been
>> >>> disabled a very long time ago, and nobody seems to have missed
>> >>> it :(
>> >>>
>> >>>
>> >>>
>> >>>> The 4.7 tree uses a lot fewer Makefile.am's and something
>> >>>> might have been missed.
>> >>>>
>> >>>> From what I see it also could be some unfinished work,
>> >>>> because it shares
>> >>>
>> >>> a lot of code with libmisc/untar (Definitely something to be
>> >>> worth looking after).
>> >>>
>> >>> Ralf
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >
>> >
>> >
>> >
>> >
>>
>>
> 
> 
> 


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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