On Wed, Dec 17, 2008 at 03:13:40PM +0100, Pavel Filipensky wrote:
> 1)
> I am wondering if I should add this comment as a warning for future
> code changes which would go OTW and cause regression of "6675447
> NFSv4 client hangs on shutdown if server is down beforehand."
>
>
> # we cannot us 'df -F nfs $mountp' to test if the given mountpoint has
> NFS on top of it
> # since df could trigger NFS over-the-wire request and cause regression of
> # "6675447 NFSv4 client hangs on shutdown if server is down beforehand."
Sure.
> 2)
> The more I am looking to umountall(1M) the more I think that
> umountall(1M) should get a new syscall and all the work apart from
> parsing the command line options should be done in the kernel.
>
> Now, the kernel exports its state via a special file system in
> /etc/mnttab. Information from /etc/mnttab is parsed as a text in
> umountall(1M) - parsing is error prone - space can do lot of harm -
> see 6786256. After the information is parsed it is processed with low
> efficiency just to get a list of mount points to be unmounted. This
> list goes back to the kernel via umount(1). Current shell
> implementation is slow and hard to maintain.
I wouldn't worry about this too much. If you use the shell built-in
read function, double quote expansions of variables containing mount
point paths, and the kernel backslash-quotes whitespace in mount point
paths in /etc/mnttab then you're OK.
> There are two pending bugs which would profit from the new umounatll
> syscall:
>
> 6733798 manpage umountall(1M) - specify what is a local/remote
> filesystem + Interface stability
> 6786256 umountall(1M) handles incorrectly mounpoints with a space
> character in the path
umountall(1M) uses read, but not correctly:
- first it reads a line at a time from mnttab to reverse the order of
mnttab
- then it echos the reversed list to a pipe to a shell function that
parses each line
The problem with that is that any backslash quoting in the original will
be lost in the first read. The Korn shell has a -r argument to read
that prevents this, but you can't use the Korn shell.
You could move /bin/tac to /usr/sbin and then use tac(1) to do the
reversing. THEN the read in domounts() will see any backslashes and
work correctly.
To make it easier for you I wrote you the attached function to
backslash-quote white-space in strings. That way you can change the
main body of unmountall to:
249 246 while read dev mountp fstype mode dummy
if [ ! -x /usr/bin/tail ]; then
exec < $MNTTAB
REVERSED=
while read dev mountp rest; do
bquote mountp
if [ -n "$REVERSED" ]; then
REVERSED="$dev $bquoted $rest\n$REVERSED"
else
REVERSED="$dev $bquoted $rest"
fi
done
error=`echo $REVERSED | doumounts`
else
error=`tail -r $MNTTAB | doumounts`
fi
Yes, I'm assuming that mnttab backslash-quotes whitespace.
Nico
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