Date: Thu, 12 Jan 2012 20:47:18 +0100 From: Dirk-Willem van Gulik <dirkx@webweaving.org> To: Matthew Story <matthewstory@gmail.com> Cc: freebsd-bugs@freebsd.org, freebsd-gnats-submit@freebsd.org Subject: Re: conf/164048: /etc/rc.d/hostid is not symlink aware Message-ID: <32429C77-4BC1-44E3-BAF8-AB5A97058E9B@webweaving.org> In-Reply-To: <CAB%2B9ogdrZL9znurHyg2=5ST_Szg5aWuGCncSt%2BGtaucknZiikQ@mail.gmail.com> References: <201201120815.q0C8FONo062154@red.freebsd.org> <CAB%2B9ogdrZL9znurHyg2=5ST_Szg5aWuGCncSt%2BGtaucknZiikQ@mail.gmail.com>
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On 12 jan. 2012, at 17:48, Matthew Story wrote:
> On Thu, Jan 12, 2012 at 3:15 AM, Dirk-Willem van Gulik =
<dirkx@webweaving.org> wrote:=20
> [...snip]=20
> # If ${hostid_file} already exists, we take UUID from there.
> - if [ -r ${hostid_file} ]; then
> + # If ${hostid_file} already exists, we take UUID from there. =
We use
> + # a -f rather than a -r check as the histid_file may in fact =
be
> + # a symbolic link.
>=20
> per the test man-page, `-r' tests for readability, regardless of type, =
and `-f' tests for the existence of a regular file. `-r' does include =
an implicit test for existence, so `-r' will in fact work for symlinks, =
and fail reliably if the symlink source_file does not exist (relevant =
bits from the test man-page at the bottom of this message):
=85.
> with this patch, if ${hostid_file} exists, and is non-readable, cat =
${hostid_file} will fail, and yield no $1 to hostid_set (effectively =
identical to a hostid_file that is empty). this is not the desired =
behavior:
Totally understood - but wanted to stay close to the behavior of =
dhclient-script as I understand it. And this happens to also make the =
behavior of /etc/rc.d/sshd on first run the same. Keep in mind that one =
can always set the rc variable.
...
> This line is actually why you are seeing a hostid_file on restart. =
The hostid_file does not exist on your system, and per the comment, and =
implementation, if a hostid_file does not exist, one is generated and =
set via sysctl (via the hostid_set function).
Agreed - as _set is better.
> There is a small race condition in this file (unless rc.d is doing =
some locking on hostid_file in the caller)
=85.
Right - which in this case is one we should not worry about - this is =
during boot - as the rc.d files are ran one by one; and generally not =
twice. However - the lock issue does affect /sbin/dhclient-script - and =
I've seen this behaviour there in the wild.
Dw=
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