Re: [PATCH v5 07/24] util: set the name for the 'main' thread

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Jan 09, 2026 at 12:45:03PM +0100, Paolo Bonzini wrote:
> On 1/8/26 18:03, Daniel P. Berrangé wrote:
> > The default main thread name is undefined, so use a constructor to
> > explicitly set it to 'main'. This constructor is marked to run early
> > as the thread name is intended to be used in error reporting / logs
> > which may be triggered very early in QEMU execution.
> 
> At least on Linux I don't think we want to call the pthread function.
> 
> Since pthread_setname_np writes to /proc/self/task/tid/comm, wouldn't that
> cause ps to show qemu processes as "main" instead of "qemu" or "qemu-kvm"?

Hmmm, it depends on the 'ps' options you use:

$ ./build/qemu-system-x86_64  &
[3] 3859009

⚙️ [oci:fedora-43 qemu]$ ps  | grep 3859009
3859009 pts/10   00:00:04 main
⚙️ [oci:fedora-43 qemu]$ ps -a | grep 3859009
3859009 pts/10   00:00:03 main
⚙️ [oci:fedora-43 qemu]$ ps -ax | grep 3859009
3859009 pts/10   Sl     0:03 ./build/qemu-system-x86_64
⚙️ [oci:fedora-43 qemu]$ ps -au | grep 3859009
berrange 3859009  8.6  0.1 3893224 123700 pts/10 Sl   11:49   0:04 ./build/qemu-system-x86_64
⚙️ [oci:fedora-43 qemu]$ ps -af | grep 3859009
berrange 3859009 2085609  8 11:49 pts/10   00:00:04 ./build/qemu-system-x86_64
⚙️ [oci:fedora-43 qemu]$ ps -axuwf | grep 3859009
berrange 3859009 53.4  0.1 3905536 124108 pts/10 Sl   11:49   0:03  |       \_ ./build/qemu-system-x86_64


and I hadn't noticed since I always use one of the latter
sets of options that give the true name.

> 
> Paolo
> 
> > Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> > Reviewed-by: Dr. David Alan Gilbert <dave@treblig.org>
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >   util/qemu-thread-posix.c | 6 ++++++
> >   util/qemu-thread-win32.c | 6 ++++++
> >   2 files changed, 12 insertions(+)
> > 
> > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> > index b1c127dbe3..afeac9ecad 100644
> > --- a/util/qemu-thread-posix.c
> > +++ b/util/qemu-thread-posix.c
> > @@ -22,6 +22,12 @@
> >   #include <pthread_np.h>
> >   #endif
> > +static void __attribute__((__constructor__(QEMU_CONSTRUCTOR_EARLY)))
> > +qemu_thread_init(void)
> > +{
> > +    qemu_thread_set_name("main");
> > +}
> > +
> >   static void error_exit(int err, const char *msg)
> >   {
> >       fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err));
> > diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
> > index 4d2d663a9a..8ca6429ad3 100644
> > --- a/util/qemu-thread-win32.c
> > +++ b/util/qemu-thread-win32.c
> > @@ -22,6 +22,12 @@ typedef HRESULT (WINAPI *pSetThreadDescription) (HANDLE hThread,
> >   static pSetThreadDescription SetThreadDescriptionFunc;
> >   static HMODULE kernel32_module;
> > +static void __attribute__((__constructor__(QEMU_CONSTRUCTOR_EARLY)))
> > +qemu_thread_init(void)
> > +{
> > +    qemu_thread_set_name("main");
> > +}
> > +
> >   static bool load_set_thread_description(void)
> >   {
> >       static gsize _init_once = 0;
> 

With regards,
Daniel
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