Re: [PATCH RFC] add pthread_setname_np

[Rich Felker <dalias@libc.org>]

On Wed, Sep 14, 2016 at 11:43:51PM -0400, Felix Janda wrote:
> Rich Felker wrote:
> 
> Thanks for the review!
> 
> > On Wed, Sep 14, 2016 at 11:02:16PM -0400, Felix Janda wrote:
> > > gdb's "info threads" displays the thread name.
> > > ---
> > > Should this function care about interrupted syscalls?
> > 
> > Unless it's specified not to return EINTR I'm fine with it returning
> > EINTR.
> 
> ok. Is it possible that write() is interrupted with partial data
> written (so that it won't return -1)?

That won't happen with these proc pseudo-files because the write is
required by the kernel to be atomic. If it's broken up into multiple
parts, the kernel only uses the last one.

> > >  include/pthread.h               |  1 +
> > >  src/thread/pthread_setname_np.c | 21 +++++++++++++++++++++
> > >  2 files changed, 22 insertions(+)
> > >  create mode 100644 src/thread/pthread_setname_np.c
> > > 
> > > diff --git a/include/pthread.h b/include/pthread.h
> > > index 3d2e0c4..94ef919 100644
> > > --- a/include/pthread.h
> > > +++ b/include/pthread.h
> > > @@ -214,6 +214,7 @@ struct cpu_set_t;
> > >  int pthread_getaffinity_np(pthread_t, size_t, struct cpu_set_t *);
> > >  int pthread_setaffinity_np(pthread_t, size_t, const struct cpu_set_t *);
> > >  int pthread_getattr_np(pthread_t, pthread_attr_t *);
> > > +int pthread_setname_np(pthread_t, const char *);
> > >  int pthread_tryjoin_np(pthread_t, void **);
> > >  int pthread_timedjoin_np(pthread_t, void **, const struct timespec *);
> > >  #endif
> > > diff --git a/src/thread/pthread_setname_np.c b/src/thread/pthread_setname_np.c
> > > new file mode 100644
> > > index 0000000..b7f7a4b
> > > --- /dev/null
> > > +++ b/src/thread/pthread_setname_np.c
> > > @@ -0,0 +1,21 @@
> > > +#include <fcntl.h>
> > > +#include <string.h>
> > > +#include <unistd.h>
> > > +
> > > +#include "pthread_impl.h"
> > > +
> > > +int pthread_setname_np(pthread_t thread, const char *name)
> > > +{
> > > +	int fd, status = 0;
> > > +	char f[sizeof "/proc/self/task//comm" + 7];
> > 
> > Where does 7 come from? I don't think it's correct. 3*sizeof(int) is
> > the normal lazy bound we use for %d's.
> 
> man 5 proc
> 
> says that the maximum value for a pid is about 4 million. I'm fine with
> to changing it to the usual lazy bound, though.

Ah. That may be true for all current versions of Linux, but I don't
think it counts as part of the API/ABI. The ABI limit on pids is 512M
IIRC (because high bits have special meaning in robust/PI futex ABI).

Rich