Date: Fri, 22 Aug 2008 13:29:39 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: Magic symlinks redux Message-ID: <20080822112939.GA58579@onelab2.iet.unipi.it> In-Reply-To: <g8m458$d3$1@ger.gmane.org> References: <g8kv7v$sp2$1@ger.gmane.org> <20080822090448.GB57441@onelab2.iet.unipi.it> <48AE89DC.9080408@yandex.ru> <g8m458$d3$1@ger.gmane.org>
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On Fri, Aug 22, 2008 at 12:24:41PM +0200, Ivan Voras wrote:
> Andrey V. Elsukov wrote:
...
>
> >This was so long ago.. As i remember this patch is a quick port of
> >NetBSD's implementation and uses the same code.
> >
> >Also there was another implementation ported from DragonFlyBSD.
...
> This patch is huge. As far as I can tell DragonflyBSD has a whole
> framework dedicated to varsyms, spread across a fair part of the kernel
> and with at least one special userland utility. It allows the operator
> to define his own variables that can be used in the substitutions, and I
> don't see that it predefines "special" variables like "uid" and
> "hostname". It's not necessarily a bad solution but I consider it overkill.
>
> Anyway, the syntax of DFBSD's varsyms is similar but sufficiently
> different from NetBSD's magicsyms implementation that both can coexist.
> DFBSD uses ${var} and NetBSD uses @var or @{var} so there's no
> ambiguity between them.
>
> Unless a kernel developer is interested in working the DFBSD's
> implementation in, I'll push the NetBSD's variant.
i also believe the simple solution is much more interesting.
However i believe a crucial issue (in terms of implementation) is
to define exactly the behaviour in error or corner cases, namely:
+ what to do if we try to expand @{nonexistentkeyword} ?
i suppose leave the string as-is is the right thing.
+ what to do if, as a result of the expansion, we exceed MAXPATHLEN ?
here it is really unclear whether returning the original
is ok, or there is a way to report some kind of error.
Also what is the exact syntax for @var ? From the code it seems
to be allowed only as the last component of a pathname i.e.
/foo/@bar is valid
/foo/@bar/ is not valid
and this makes me wonder why one should support this syntax at all,
rather than just using
/foo/@{bar}
which achieves the same thing, is legal in all contexts, has
a lower chance of conflicting with existing pathnames and
makes the code simpler!
cheers
luigi
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