man/io_uring_get_probe.3: make a note of returning NULL if not supported
5.5 and earlier don't have the register probe opcode, and hence the
library function will return NULL in that case.
@@ -18,6 +18,10 @@ The function io_uring_get_probe() returns an allocated io_uring_probe
structure to the caller. The caller is responsible for freeing the
structure with the function io_uring_free_probe().
+.SH NOTES
+Earlier versions of the Linux kernel does not support probe. If the kernel
+doesn't support probe, this function will return NULL.
+
.SH RETURN VALUE
On success it returns an allocated io_uring_probe structure, otherwise
it returns NULL.
