Re: [PATCH RFC] add pthread_setname_np

[Felix Janda <felix.janda@posteo.de>]

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)?

> > ---
> >  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.

> > +	ssize_t len;
> > +
> > +	if ((len = strlen(name)) > 15) return ERANGE;
> 
> Storing the result of strlen in a ssize_t is odd. It works because no
> object can be larger than SIZE_MAX/2, but it's ugly. Also using
> strnlen would be preferable if there's a limit (so as not to read
> unboundedly long strings only to reject them).

ssize_t is a remnant from reusing len for the return value of write().
Will fix both issues.

> > +
> > +	snprintf(f, sizeof f, "/proc/self/task/%d/comm", thread->tid);
> > +	if ((fd = open(f, O_WRONLY)) < 0) return errno;
> > +	if (write(fd, name, len) < 0) status = errno;
> > +
> > +	close(fd);
> 
> This needs blocking of the cancellation points, I think.

Will look into it.

Thanks,
Felix