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

[Martin Kletzander]

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 at linux.vnet.ibm.com>
>---
> 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.
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