Re: [Xen-devel] [PATCH] docs: document handling of metacharacter escape in xl disk format

[Jim Fehlig <jfehlig@xxxxxxxx>]

On 02/19/2016 03:14 AM, Ian Campbell wrote:
> On Thu, 2016-02-18 at 15:44 -0700, Jim Fehlig wrote:
>> Ian Campbell wrote:
>>> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>>> Cc: Jim Fehlig <jfehlig@xxxxxxxx>
>>> ---
>>>  docs/misc/xl-disk-configuration.txt | 18 ++++++++++++++++++
>>>  1 file changed, 18 insertions(+)
>>>
>>> diff --git a/docs/misc/xl-disk-configuration.txt b/docs/misc/xl-disk-
>>> configuration.txt
>>> index 6a2118d..a03ad10 100644
>>> --- a/docs/misc/xl-disk-configuration.txt
>>> +++ b/docs/misc/xl-disk-configuration.txt
>>> @@ -48,6 +48,24 @@ positionally or explicitly).
>>>  
>>>  Whitespace may appear before each parameter and will be ignored.
>>>  
>>> +Metacharacters in a <diskspec> may be escaped using a backslash:
>>> +
>>> +    Escape      HEX     Description
>>> +    ------      ---     -----------
>>> +    \a          0x07    Bell
>>> +    \b          0x08    Backspace
>>> +    \t          0x09    Horizontal Tab
>>> +    \n          0x0A    New Line / Line Feed
>>> +    \f          0x0C    Form Feed
>>> +    \r          0x0D    Carriage Return
>>> +    \v          0x0B    Vertical Tab
>>> +    \"          0x22    A literal double quote
>>> +    \'          0x27    A literal single quote
>>> +    \\          0x5C    A literal backslash
>>> +    \xXX                Character XX in hexadecimal
>>> +    \OOO                Character OOO in octal
>> Do you know how any of these would be useful in a diskspec? I guess I'm
>> struggling to understand when a 'Bell' would be needed :-).
> I've not got a clue -- these are just all the ones handled by
> xlu__cfgl_dequote, perhaps just for completeness?

Maybe this code was copied from elsewhere and the unneeded/unused escapes were
not removed. Regardless, it's probably unwise to remove things like bell, form
feed, and vertical tab now.

>
> This is applied to all strings in a cfg file, not just diskspecs, 

Ah, right. And as such, I agree with your follow-up comment that this info
should then be in xl.cfg(5).

Regards,
Jim

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