Date: Wed, 23 May 2007 11:11:54 +0200 (CEST)
From: Oliver Fromme <olli@lurza.secnetix.de>
To: freebsd-current@FreeBSD.ORG, "Ralf S. Engelschall" <rse@FreeBSD.ORG>
Subject: Re: etc/rc.d/{var,tmp} and sub-shell usage?!
Message-ID: <200705230911.l4N9Bssl015397@lurza.secnetix.de>
In-Reply-To: <20070523081749.GA18197@engelschall.com>
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Ralf S. Engelschall wrote:
> I've just stumbled over a confusing sub-shell usage in our
> src/etc/rc.d/{var,tmp} scripts where I'm sure the sub-shells are totally
> unnecessary and useless. I also do not see any difference under run-time
> except that the sub-shell usage is slower, of course ;-)
>
> Nevertheless, I'm a little bit curious whether someone else sees _ANY_
> reason to keep those sub-shell constructs? If nobody has any objections
> I would just cleanup these two scripts by removing the sub-shell
> constructs...
> [...]
> [Nn][Oo])
> ;;
> *)
> - if (/bin/mkdir -p /tmp/.diskless 2> /dev/null); then
> + if /bin/mkdir -p /tmp/.diskless 2> /dev/null; then
> rmdir /tmp/.diskless
> else
> if [ -h /tmp ]; then
Additionally, I think it's not a good idea to use
"mkdir -p" to check if a directory is writable.
If the directory already exists (for whatever
reason), "mkdir -p" succeeds even if the file
system is not writable.
Normally you would use touch(1), but the problem
is that touch is in /usr, so it might not be
available in single-user mode (which is probably
the reason why the original author used mkdir in
the first place).
The best solution is probably to use /bin/ln, and
include the PID in the name to reduce the risk of
accidental file name collisions. (Note that this
code is running before the system is multi-user,
so writing to /tmp as root doesn't introduce a
security issue here, as far as I can tell.)
test_file=/tmp/.diskless.$$
if /bin/ln -sf foo $test_file 2>/dev/null; then
rm $test_file
else
[...]
fi
Well ... Thinking about it, there's a good chance
that the PID is always the same during the boot
sequence of scripts (some low number anyway), so
maybe something like $(/bin/date +%s) should be
used in the name of the test file instead od the
PID. But maybe that's just overkill.
Best regards
Oliver
PS: I also noticed that there's really a lot of
redundant (i.e. superfluous) use of braces "${}"
for variable expansion in the scripts, which makes
them more difficult to read (IMHO). Is there some
style guideline that requires it? Just wondering ...
--
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
Handelsregister: Registergericht Muenchen, HRA 74606, Geschäftsfuehrung:
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