Re: [Qemu-devel] [RFC PATCH 2/4] qmp/hmp: Add getfd_file monitor command

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

On 05/21/2012 05:48 PM, Eric Blake wrote:
> On 05/21/2012 02:19 PM, Corey Bryant wrote:
>> This patch provides support for the getfd_file monitor command.
>> This command will allow passing of a filename and its corresponding
>> file descriptor to a guest via the monitor.  This command could be
>> followed, for example, by a drive_add command to hot attach a disk
>> drive.
>>
>> Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>
>
> Is the only difference between 'getfd' and 'getfd_file' the fact that
> 'getfd' introduces an abstract namespace usable only by the fd:
> protocol, while the 'getfd_file' introduces a name identical to the
> absolute naming of the file system and usable by the file: protocol?

The only difference is that getfd passes an fdname to associate to the 
fd, and getfd_file passes a filename to associate to the fd.  These 
name/fd pairs are stored separately so there won't be any conflicts (ie. 
fdname == filename).

> What happens if I pass 'getfd_file' a relative file name?  Must the
> filename passed to 'getfd_file' be in canonical form, or may it contain
> symlinks, .., and other non-canonical constructs?

As the code is now, the 'getfd_file' filename has to be the same as the 
'drive_add' filename, for example.  And the same goes for the '-drive' 
filename and the '-filfd' filename.  I didn't introduce any special 
handling to canonicalize the filenames, but I think it is necessary. 
Either in QEMU or libvirt, but it probably makes more sense to 
canonicalize in QEMU.

>
> Can the 'closefd' command be used to close the fd originally given to
> qemu via 'getfd_file'?
>

No, 'closefd' won't close an fd passed in by 'getfd_file'.  I was 
thinking I should probably add a 'closefd_file' that could do this.


-- 
Regards,
Corey