Re: [libvirt] [PATCH 3/3] qemu: Pass file descriptor when using TPM passthrough

On 02/24/2015 09:08 AM, Martin Kletzander wrote: >On Mon, Feb 23, 2015 at 06:50:48AM -0500, Stefan Berger wrote: >>Pass the TPM file descriptor to QEMU via command line. >>Instead of passing /dev/tpm0 we now pass /dev/fdset/10 and the >>additional >>parameters -add-fd set=10,fd=20. >> >>This addresses the use case when QEMU is started with non-root >>privileges >>and QEMU cannot open /dev/tpm0 for example. >> >>Signed-off-by: Stefan Berger <stefanb(a)linux.vnet.ibm.com&gt; >>--- >>src/qemu/qemu_command.c | 121 >>++++++++++++++++++++++++++++++++++++++++++++++-- >>1 file changed, 117 insertions(+), 4 deletions(-) >> >>diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c >>index 539c956..12e2e2f 100644 >>--- a/src/qemu/qemu_command.c >>+++ b/src/qemu/qemu_command.c >>@@ -161,6 +161,58 @@ VIR_ENUM_IMPL(qemuNumaPolicy, >>VIR_DOMAIN_NUMATUNE_MEM_LAST, >> "interleave"); >> >>/** >>+ * qemuVirCommandGetFDSet: >>+ * @cmd: the command to modify >>+ * @fd: fd to reassign to the child >>+ * >>+ * Get the parameters for the QEMU -add-fd command line option >>+ * for the given file descriptor. The file descriptor must previously >>+ * have been 'transferred' in a virCommandPassFD() call. >>+ * This function for example returns "set=10,fd=20". >>+ */ >>+static char * >>+qemuVirCommandGetFDSet(virCommandPtr cmd, int fd) >>+{ >>+ char *result = NULL; >>+ int idx = virCommandPassFDGetFDIndex(cmd, fd); >>+ >>+ if (idx >= 0) { >>+ ignore_value(virAsprintf(&result, "set=%d,fd=%d", idx, >>fd) < 0); >^ >This line doesn't make much sense, I guess you just wanted to do it | >without the comparison to zero here ---------------------------------+ > >Anyway, is there a reason for passing "set=X,fd=Y" instead of just >doing fd=Y and being done with it? I must admit I don't know the >details of /dev/fdset, so that might've just missed me. Passing fd by itself is not supported with this device. I guess back then when I implemented I knew I could pass the fd via this /dev/fdset and so fd= doesn't need to be implemented on top of that.