Re: [PATCH RFC] add pthread_setname_np

[Rich Felker <dalias@libc.org>]

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.

> ---
>  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.

> +	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).

> +
> +	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.

Rich