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.
A point in your favor, for at least testing what you parse! If we change our mind to mimic shell or C parsing, then we'd have to update these tests.
Yes, escaping rules blow my mind unless I can test them :-)
You're not the only one - I added loads of tests when I added shell parsing to virsh.
Overall, I like the idea of the new function, but I'm worried that introducing yet another parser could hurt us (users will be asking "now which escape style is in effect here, and how does it differ from standardized escape styles that I'm used to?").
I think that perhaps we should have virStrSplitQuoted just return the split pieces, with *no* unescaping. And then have separate functions to escape/unescape individual string pieces after the fact.
Except that you then have to know what quoting styles were in use to know whether \ was a literal or an escape. -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org