Re: [PATCH v2 5/5] qemu_passt: Let passt write the PID file

[Laine Stump <laine@redhat.com>]

On 2/16/23 8:32 AM, Michal Privoznik wrote:
> The way we start passt currently is: we use
> virCommandSetPidFile() to use our virCommand machinery to acquire
> the PID file and leak opened FD into passt. Then, we use
> virPidFile*() APIs to read the PID file (which is needed when
> placing it into CGroups or killing it). But this does not fly
> really because passt daemonizes itself. Thus the process we
> started dies soon and thus the PID file is closed and unlocked.
> 
> We could work around this by passing '--foreground' argument, but
> that weakens passt as it can't create new PID namespace (because
> it doesn't fork()).
> 
> The solution is to let passt write the PID file, but since it
> does not lock the file and closes it as soon as it is written, we
> have to switch to those virPidFile APIs which don't expect PID
> file to be locked.

So *this* is the part that was functionally wrong after my earlier patch 
was applied - I had switched to using an externally-generated pidfile, 
but was still using the APIs that should have only been used for 
pidfiles created by libvirt.

(You had mentioned some sort of cgroup issue last week. Did that solve 
itself? I never saw the problem, and passt has been starting/stopping 
fine for me all along (both before and after I changed the daemonizing) 
as long as selinux is disabled - still need to fix that).

> 
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

Reviewed-by: Laine Stump <laine@redhat.com>

> ---
>   src/qemu/qemu_passt.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/src/qemu/qemu_passt.c b/src/qemu/qemu_passt.c
> index a4cc9e7166..47f4b5fcae 100644
> --- a/src/qemu/qemu_passt.c
> +++ b/src/qemu/qemu_passt.c
> @@ -72,7 +72,7 @@ qemuPasstGetPid(virDomainObj *vm,
>   {
>       g_autofree char *pidfile = qemuPasstCreatePidFilename(vm, net);
>   
> -    return virPidFileReadPathIfLocked(pidfile, pid);
> +    return virPidFileReadPath(pidfile, pid);
>   }
>   
>   
> @@ -106,11 +106,14 @@ static void
>   qemuPasstKill(const char *pidfile)
>   {
>       virErrorPtr orig_err;
> +    pid_t pid = 0;
>   
>       virErrorPreserveLast(&orig_err);
>   
> -    if (virPidFileForceCleanupPath(pidfile) < 0)
> -        VIR_WARN("Unable to kill passt process");
> +    ignore_value(virPidFileReadPath(pidfile, &pid));
> +    if (pid != 0)
> +        virProcessKillPainfully(pid, true);
> +    unlink(pidfile);
>   
>       virErrorRestore(&orig_err);
>   }
> @@ -161,13 +164,13 @@ qemuPasstStart(virDomainObj *vm,
>       cmd = virCommandNew(PASST);
>   
>       virCommandClearCaps(cmd);
> -    virCommandSetPidFile(cmd, pidfile);
>       virCommandSetErrorBuffer(cmd, &errbuf);
>   
>       virCommandAddArgList(cmd,
>                            "--one-off",
>                            "--socket", passtSocketName,
>                            "--mac-addr", virMacAddrFormat(&net->mac, macaddr),
> +                         "--pid", pidfile,
>                            NULL);
>   
>       if (net->mtu) {