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

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? 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?