add pthread_getname_np function

based on the pthread_setname_np implementation

include/pthread.h

@@ -221,6 +221,7 @@ 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_getname_np(pthread_t, char *, size_t);
 int pthread_getattr_default_np(pthread_attr_t *);
 int pthread_setattr_default_np(const pthread_attr_t *);
 int pthread_tryjoin_np(pthread_t, void **);

src/thread/pthread_getname_np.c

@@ -0,0 +1,25 @@
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/prctl.h>
+
+#include "pthread_impl.h"
+
+int pthread_getname_np(pthread_t thread, char *name, size_t len)
+{
+	int fd, cs, status = 0;
+	char f[sizeof "/proc/self/task//comm" + 3*sizeof(int)];
+
+	if (len < 16) return ERANGE;
+
+	if (thread == pthread_self())
+		return prctl(PR_GET_NAME, (unsigned long)name, 0UL, 0UL, 0UL) ? errno : 0;
+
+	snprintf(f, sizeof f, "/proc/self/task/%d/comm", thread->tid);
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+	if ((fd = open(f, O_RDONLY|O_CLOEXEC)) < 0 || (len = read(fd, name, len)) < 0) status = errno;
+	else name[len-1] = 0; /* remove trailing new line only if successful */
+	if (fd >= 0) close(fd);
+	pthread_setcancelstate(cs, 0);
+	return status;
+}