Re: [RFC 0/7] [RFC] cramfs: fake write support

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From: Erez Zadok
Date: Sunday, June 1, 2008 - 9:37 pm

> Jan Engelhardt wrote:

I agree w/ Jan E.

Folks, I've said it before: unioning is a deceptively simple idea in
principle, and &^@%*$&^@ hard in practice.  And anyone who thinks otherwise
is welcome to write a *versatile* unioning implementation on their own.  Once
you get through all corner cases and satisfy all the features which users
want, you have a complex large file system.

I believe that implementing unioning inside actual filesystems is totally the
wrong direction: going to lower layers is wrong, instead of going up to a
VFS-based solution.  Unioning is a namespace operation that should not be
done deep inside a lower f/s.

People often wonder why FScache is (reportedly) so complex and big.  It's
b/c in some part it has to deal with similar issues: unioning is
copy-on-write, whereas caching is copy-on-read.

Nevertheless, I can understand if the embedded community wants lightweight
unioning.  Union Mounts initially may not support everything that unionfs
does, but it should be smaller, and it should be enough I believe for the
basic unioning uses --- perhaps even for the embedded community.  If so,
then I suggest people offer to help Bharata and Jan Blunk's efforts, rather
than [sic] cramming unioning into a single file system.

Erez.
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Messages in current thread:
[RFC 0/7] [RFC] cramfs: fake write support, arnd, (Sat May 31, 8:37 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, David Newall, (Sat May 31, 11:56 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Sat May 31, 1:40 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Phillip Lougher, (Sat May 31, 8:19 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Phillip Lougher, (Sat May 31, 8:54 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support, David Newall, (Sat May 31, 11:02 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Sun Jun 1, 1:52 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Jan Engelhardt, (Sun Jun 1, 2:11 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Jamie Lokier, (Sun Jun 1, 5:28 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Sun Jun 1, 2:49 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support , hooanon05, (Sun Jun 1, 7:48 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support , Erez Zadok, (Sun Jun 1, 8:25 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support , Erez Zadok, (Sun Jun 1, 8:51 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support , Erez Zadok, (Sun Jun 1, 9:37 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Bharata B Rao, (Sun Jun 1, 11:07 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Mon Jun 2, 12:12 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support , Jan Engelhardt, (Mon Jun 2, 12:17 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Mon Jun 2, 12:51 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support , hooanon05, (Mon Jun 2, 3:36 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Jamie Lokier, (Mon Jun 2, 4:07 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Mon Jun 2, 4:15 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support , hooanon05, (Mon Jun 2, 5:56 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Mon Jun 2, 7:13 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support , hooanon05, (Mon Jun 2, 7:33 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Evgeniy Polyakov, (Mon Jun 2, 7:54 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Mon Jun 2, 8:01 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support , Erez Zadok, (Mon Jun 2, 8:35 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Arnd Bergmann, (Mon Jun 2, 10:42 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support , Erez Zadok, (Mon Jun 2, 11:13 am)
Re: [RFC 0/7] [RFC] cramfs: fake write support, Phillip Lougher, (Mon Jun 2, 7:02 pm)
Re: [RFC 0/7] [RFC] cramfs: fake write support , hooanon05, (Tue Jun 3, 4:04 am)