On Fri, 14 Oct 2022 10:51:36 +0200
Paolo Bonzini <pbonz...@redhat.com> wrote:
> On 10/14/22 08:08, Greg Kurz wrote:
> >
> > + need_to_open_file = log_flags && !per_thread;
>
> Pre-existing, but I think this should check log_per_thread instead of
> per_thread.
>
Yes I agree, and also check qemu_loglevel instead of log_flags for
the same reason (and to match the comment just above).
> > + } else if (filename) {
> > + /*
> > + * If we are daemonized, we will only log if there is a filename.
> > + */
> > + need_to_open_file = true;
>
> Slightly nicer:
>
> } else {
> /*
> * If daemonized, always log to the -D file if present.
> */
> need_to_open_file = filename != NULL;
> }
>
Sure.
> > @@ -271,10 +276,22 @@ static bool qemu_set_log_internal(const char
> > *filename, bool changed_name,
> >
> > if (!logfile && need_to_open_file) {
> > if (filename) {
> > - logfile = fopen(filename, log_append ? "a" : "w");
> > + g_autofree char *fname = NULL;
> > +
> > + /*
> > + * If per-thread, filename contains a single %d that should be
> > + * converted.
> > + */
> > + if (per_thread) {
> > + fname = g_strdup_printf(filename, getpid());
> > + } else {
> > + fname = g_strdup(filename);
> > + }
> > +
> > + logfile = fopen(fname, log_append ? "a" : "w");
> > if (!logfile) {
> > error_setg_errno(errp, errno, "Error opening logfile %s",
> > - filename);
> > + fname);
> > return false;
> > }
> > /* In case we are a daemon redirect stderr to logfile */
>
> This could conflict with the file opened by qemu_log_trylock() when
> per-thread logging is enabled *and* QEMU is daemonized. Perhaps
> something like:
>
Yeah... if the main thread happens to call qemu_log(), it then opens
a file with the same name indeed. Thanks for catching that !
> 1) change qemu_log_trylock() to
>
> - if (log_per_thread) {
> + if (log_per_thread && log_thread_id() != getpid()) {
>
> i.e. use the global_file for the main thread
>
> 2) change qemu_log_unlock() to
>
> - if (!log_per_thread) {
> + if (!thread_file) {
>
> to match (1)
>
> 3) change log_thread_id() to something like
>
> ...
> #else
> static __thread int my_id = -1;
> static int counter;
> if (my_id == -1) {
> my_id = getpid() + qatomic_fetch_inc(&counter);
> }
> return my_id;
> #endif
>
> and perhaps do a dummy trylock/unlock late in qemu_set_log_internal(),
> to ensure that the main thread is the one with log_thread_id() == getpid()?
>
> I think this can be a separate patch before this one.
>
2) and 3) can certainly be preparatory work but I think 1)
should be squashed in my patch. Because of the !per_thread
check in need_to_open_file, the existing code in
qemu_set_log_internal() doesn't even open the global file
and qemu_log_trylock() would always return NULL for the
main thread.
Thanks for the quick answer and suggestions !
> Paolo
>
