1 files changed, 22 insertions, 0 deletions

diff --git a/lib/libc/sys/ioctl.2 b/lib/libc/sys/ioctl.2
index 36ce6ff47f652..38c58b9dcf592 100644
--- a/lib/libc/sys/ioctl.2
+++ b/lib/libc/sys/ioctl.2
@@ -68,6 +68,28 @@ Macros and defines used in specifying an ioctl
 .Fa request
 are located in the file
 .Ao Pa sys/ioctl.h Ac .
+.Sh IMPLEMENTATION NOTES
+.Pp
+In the non-threaded library
+.Fn ioctl
+is implemented as the
+.Va ioctl
+syscall.
+.Pp
+In the threaded library, the
+.Va ioctl
+syscall is assembled to
+.Fn _thread_sys_ioctl
+and
+.Fn ioctl
+is implemented as a function which locks
+.Va d
+for read and write, then calls
+.Fn _thread_sys_ioctl .
+Before returning,
+.Fn ioctl
+unlocks
+.Va d .
 .Sh RETURN VALUES
 If an error has occurred, a value of -1 is returned and
 .Va errno