Re: [PATCH v2 03/14] system: unconditionally enable thread naming

["Ján Tomko" <jtomko@redhat.com>]

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On a Friday in 2025, Daniel P. Berrangé wrote:
>When thread naming was introduced years ago, it was disabled by
>default and put behind a command line flag:
>
>  commit 8f480de0c91a18d550721f8d9af969ebfbda0793
>  Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
>  Date:   Thu Jan 30 10:20:31 2014 +0000
>
>    Add 'debug-threads' suboption to --name
>
>This was done based on a concern that something might depend
>on the historical thread naming. Thread names, however, were
>never promised to be part of QEMU's public API. The defaults
>will vary across platforms, so no assumptions should ever be
>made about naming.
>
>An opt-in behaviour is also unfortunately incompatible with
>RCU which creates its thread from an constructor function
>which is run before command line args are parsed. Thus the
>RCU thread lacks any name.
>
>libvirt has unconditionally enabled debug-threads=yes on all
>VMs it creates for 10 years. Interestingly this DID expose a
>bug in libvirt, as it parsed /proc/$PID/stat and could not
>cope with a space in the thread name. This was a latent
>pre-existing bug in libvirt though, and not a part of QEMU's
>API.
>
>Having thread names always available, will allow thread names
>to be included in error reports and log messags QEMU prints
>by default, which will improve ability to triage QEMU bugs.
>
>Reviewed-by: Dr. David Alan Gilbert <dave@treblig.org>
>Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
>---
> docs/about/deprecated.rst |  7 +++++++
> include/qemu/thread.h     |  1 -
> system/vl.c               | 11 ++++++-----
> util/qemu-thread-posix.c  | 18 +-----------------
> util/qemu-thread-win32.c  | 27 ++++++---------------------
> 5 files changed, 20 insertions(+), 44 deletions(-)
>
>diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
>index d50645a071..bd6f865558 100644
>--- a/docs/about/deprecated.rst
>+++ b/docs/about/deprecated.rst
>@@ -81,6 +81,13 @@ kernel since 2001. None of the board types QEMU supports need
> ``param_struct`` support, so this option has been deprecated and will
> be removed in a future QEMU version.
>
>+``debug-threads`` option for ``-name``

(since 10.2)

Jano

>+''''''''''''''''''''''''''''''''''''''
>+
>+Thread ``debug-threads`` option for the ``-name`` argument is now
>+ignored. Thread naming is unconditionally enabled for all platforms
>+where it is supported.
>+
> User-mode emulator command line arguments
> -----------------------------------------
>

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