Re: [Qemu-devel] [PATCH] Modify qemu-img can not create local filename contain ":"

[Max Reitz <mreitz@redhat.com>]

On 03.03.2014 19:03, Eric Blake wrote:
> On 03/03/2014 10:47 AM, Max Reitz wrote:
>
>> Currently, a protocol prefix is only defined to end with a colon, not
>> with ":/" or "://". There are already protocol block drivers which do
>> not require a slash after the colon such as blkdebug or blkverify and I
>> deem it rather impossible to redefine their filename format now (in
>> order to make them use ":/").
> It should ALWAYS be possible to open a file via absolute path, or via
> './file:with:colon'.  That is, our check for a protocol should be any
> prefix that contains a ':' prior to a '/'.

Oh, yes, you are right, I forgot about that.

Max

>
>> Thus, I do not think it will be this easy. I am in fact not even sure
>> whether it is possible at all (automagically doing the right thing) –
>> currently, a colon simpy is the separator between protocol and filename.
>> Just using the "file" protocol per default for the whole filename if
>> there is no protocol with a name equal to the pre-colon part is probably
>> not what we want, since the user may actually be referring to some
>> protocol that the qemu version he/she is using does not support (yet),
>> in which case creating a file with a name including the pre-colon part
>> (the protocol name) is most probably not the right thing to do.
> If the user wants a file name that contains a colon, use either an
> absolute path name, or prefix the relative name with './'.  Either way
> should cause a '/' to occur before the first ':', and since a protocol
> consists only of a prefix prior to ':' without '/', it then becomes
> obvious that a file name is intended.
>
>> Henceforth, in my opinion, we either have to ask the user in that case
>> or we introduce some new option which disables protocol prefixes. I
>> think the easiest way to do the latter is to introduce a
>> bdrv_parse_filename() function for the "file" protocol drivers which
>> remove a "file:" prefix if given. Then, the user could just specify
>> "file:foo:bar.img" to reference a file named "foo:bar.img".
> Yes, this would also make sense, if you can't live with './foo:bar.img'.
>
>> Currently, the behavior is that such a prefix will be interpreted
>> correctly (the "file" protocol is selected) but it is not removed. Thus,
>> "file:foo:bar.img" will actually reference a file named
>> "file:foo:bar.img". One could argue that removing the prefix therefore
>> breaks current behavior, but I sincerely hope nobody has relied on that
>> behavior so far.
> I think the fact that the file: prefix is NOT removed before hitting the
> filesystem is a bug worth fixing - it should be fairly obvious that the
> relative name in the filesystem should not include the 'file:' prefix,
> but that 'file:' was the protocol that forced interpretation of the rest
> of the string as a local filename.
>