Re: [Qemu-devel] [RFC PATCH 0/4] block: file descriptor passing using -filefd and getfd_file

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

On 05/22/2012 04:18 AM, Kevin Wolf wrote:
> Am 21.05.2012 22:19, schrieb Corey Bryant:
>> libvirt's sVirt security driver provides SELinux MAC isolation for
>> Qemu guest processes and their corresponding image files.  In other
>> words, sVirt uses SELinux to prevent a QEMU process from opening
>> files that do not belong to it.
>>
>> sVirt provides this support by labeling guests and resources with
>> security labels that are stored in file system extended attributes.
>> Some file systems, such as NFS, do not support the extended
>> attribute security namespace, and therefore cannot support sVirt
>> isolation.
>>
>> A solution to this problem is to provide fd passing support, where
>> libvirt opens files and passes file descriptors to QEMU.  This,
>> along with SELinux policy to prevent QEMU from opening files, can
>> provide image file isolation for NFS files.
>>
>> This patch series adds the -filefd command-line option and the
>> getfd_file monitor command.  This will enable libvirt to open a
>> file and push the corresponding filename and file descriptor to
>> QEMU.  When QEMU needs to "open" a file, it will first check if the
>> file descriptor was passed by either of these methods before
>> attempting to actually open the file.
>
> I thought we decided to avoid making some file names magic, and instead
> go for the obvious /dev/fd/42?
>
> Kevin
>

I understand that open("/dev/fd/42") would be the same as dup(42), but 
I'm not sure that I'm entirely clear on how this would work.  Could you 
give an example?

-- 
Regards,
Corey