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Re: [libvirt] [PATCH] Add a virStrSplitQuoted for splitting quoted strings



On Wed, Mar 14, 2012 at 11:10:24AM -0600, Eric Blake wrote:
> On 03/14/2012 10:50 AM, Daniel P. Berrange wrote:
> >> This looks like it is repeating some of the code in
> >> virsh.c:vshCommandStringGetArg; any chance we can combine them?  In
> >> particular, the ability to mimic shell handling of \ escapes, as well as
> >> the difference in behavior of \ inside "" vs. '', seems like it will
> >> come in handy.
> > 
> > Ah I had forgotten about that code. Can you clarify the difference
> > in \ handling.  I guess you mean that inside '', \ can only be used
> > for  \\ and \', while inside "", it can do all the standard shell
> > escapes like \t, \n, etc ?
> 
> Inside '', \ has no special meaning. (There's no way to escape ' inside
> of ').
> 
> Inside "", \ escapes the next byte (important for " and \, but works on
> any byte.
> 
> Outside quotes, \ escapes the next byte.
> 
> And most importantly: concatenating two forms of quoted materials is
> permitted.  Thus:
> 
> foo"b'ar\" "\'' blah\'
> 
> on input becomes this on output:
> 
> foob'ar" ' blah\
> 
> >>
> >> What you have here does neither; although I didn't spot any flaw in the
> >> code, I don't know if it's the algorithm we want to be using.
> > 
> > I should have sent this paired with my other patch for <cmdline>
> > handling in LXC. That is the intended use case for this function.
> > 
> > I'm not sure that anyone has ever clearly defined what escaping
> > syntax is used for /proc/cmdline (which is what <cmdline> is
> > representing.
> 
> Hmm, good point.  If it is /bin/sh doing the parsing, then we know the
> rules (and virsh matches them); but it if is a custom parser in the
> kernel, the we have to match that custom parser.

Hmm, well actually there are multiple consumers of /proc/cmdline
data.

 - kernel
 - init
 - userspace (eg anaconda)

What is the betting that everyone has their own rules :-)

For LXC's purposes though, we don't care about the kernel, only
init. So I guess I should look at what upstart/sysvinit/systemd
do for parsing rules

Daniel
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