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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