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

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.