thr_set_name(): silently truncate the given name as needed

Instead of failing with ENAMETOOLONG, which is swallowed by
pthread_set_name_np() anyway, truncate the given name to MAXCOMLEN+1
bytes.  This is more likely what the user wants, and saves the
caller from truncating it before the call (which was the only
recourse).

Polish pthread_set_name_np(3) and add a .Xr to thr_set_name(2)
so the user might find the documentation for this behavior.

Reviewed by:	jilles
MFC after:	3 days
Sponsored by:	Dell EMC

1 files changed, 5 insertions, 2 deletions

diff --git a/sys/kern/kern_thr.c b/sys/kern/kern_thr.c
index 10e7b2d0ecd1..55c4ae4007ce 100644
--- a/sys/kern/kern_thr.c
+++ b/sys/kern/kern_thr.c
@@ -578,8 +578,11 @@ sys_thr_set_name(struct thread *td, struct thr_set_name_args *uap)
 	error = 0;
 	name[0] = '\0';
 	if (uap->name != NULL) {
-		error = copyinstr(uap->name, name, sizeof(name),
-			NULL);
+		error = copyinstr(uap->name, name, sizeof(name), NULL);
+		if (error == ENAMETOOLONG) {
+			error = copyin(uap->name, name, sizeof(name) - 1);
+			name[sizeof(name) - 1] = '\0';
+		}
 		if (error)
 			return (error);
 	}