[PATCH] man: Fix syscall wrappers in example code

["Martin K. Petersen" <martin.petersen@oracle.com>]

The example code in io_uring.7 provides two wrappers for the io_uring
syscalls. However, the example fails to take into account that glibc's
syscall(2) returns -1 and sets errno on failure. This means that any
errors returned by the provided wrapper functions will be reported as
-EPERM which could lead to incorrect error handling actions being
taken.

Adjust the two example wrappers to match arch/generic/syscall.h. This
makes them follow the documented io_uring calling convention which
reports a call error as a negative return value.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/man/io_uring.7 b/man/io_uring.7
index 49cdc25290e7..b6c092b60201 100644
--- a/man/io_uring.7
+++ b/man/io_uring.7
@@ -651,14 +651,18 @@ off_t offset;
 
 int io_uring_setup(unsigned entries, struct io_uring_params *p)
 {
-    return (int) syscall(__NR_io_uring_setup, entries, p);
+    int ret;
+    ret = syscall(__NR_io_uring_setup, entries, p);
+    return (ret < 0) ? -errno : ret;
 }
 
 int io_uring_enter(int ring_fd, unsigned int to_submit,
                    unsigned int min_complete, unsigned int flags)
 {
-    return (int) syscall(__NR_io_uring_enter, ring_fd, to_submit,
-    			 min_complete, flags, NULL, 0);
+    int ret;
+    ret = syscall(__NR_io_uring_enter, ring_fd, to_submit,
+                  min_complete, flags, NULL, 0);
+    return (ret < 0) ? -errno : ret;
 }
 
 int app_setup_uring(void) {