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Re: [Xen-devel] [PATCH v1 1/6] docs: add feature document for Xen hypervisor sysfs-like support

On 27.09.19 17:19, Ian Jackson wrote:
Jürgen Groß writes ("Re: [PATCH v1 1/6] docs: add feature document for Xen 
hypervisor sysfs-like support"):
On 27.09.19 15:37, Ian Jackson wrote:
I think this is ASCII printing characters with the exception of
    ! " ` $ % ^ & * = + { } ' ~ < > / \ |

I struggle to find a principled explanation for this particular
exclusion set (apart from /), considering that following are
    - @ _ . : ( ) [ ] # , ;

Could we borrow some existing permitted character set ?  If we are
permitting shell metacharacters why not just permit all printable
ASCII except / ?

Hmm, maybe we should allow just the "Posix portable file name character
set"? That would be [-._0-9A-Za-z]. And we should explicitly not allow
the key names "." and "..".

I agree about "." and "..".

I'm not sure the "Posix portable file name character set" is a very
good guide.  Posix will be pretty restricted there.  What is the legal
set in a Linux sysfs filename ?

Everything but "/" and "\0".

Do you mean "any 7-bit byte", or octet values 32-126 (0x20-0x7e)
inclusive, or something else ?


As I'd like to support e.g. the .config file contents of the hypervisor
build I guess I need (0x01-0xff) inclusive, right?

The .config file I have here does not seem to contain any control
characters.  If it did surely that would be a bug?  If you want this
you obviously do need to permit newlines and spaces and perhaps tabs

.config can contain user supplied strings. While not making much sense
to have unprintable characters in there I don't see how to prevent them.
And I guess we'd want to see them in case such a weird .config was used
(and probably resulted in strange behavior).


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