hurd: Refactor readlinkat()

Make the code flow more linear using early returns where possible. This
makes it so much easier to reason about what runs on error / successful
code paths.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230212111044.610942-2-bugaevc@gmail.com>

diff --git a/sysdeps/mach/hurd/readlinkat.c b/sysdeps/mach/hurd/readlinkat.c
index 1efb09c..dabdbb3 100644 (file)
--- a/sysdeps/mach/hurd/readlinkat.c
+++ b/sysdeps/mach/hurd/readlinkat.c
@@ -31,38 +31,47 @@ __readlinkat (int fd, const char *file_name, char *buf, size_t len)
   error_t err;
   file_t file_stat;
   struct stat64 st;
+  enum retry_type doretry;
+  char retryname[1024];
+  file_t file;
+  char *rbuf = buf;
 
   file_stat = __file_name_lookup_at (fd, 0, file_name, O_NOLINK, 0);
   if (file_stat == MACH_PORT_NULL)
     return -1;
 
   err = __io_stat (file_stat, &st);
-  if (! err)
-    if (S_ISLNK (st.st_mode))
-      {
-       enum retry_type doretry;
-       char retryname[1024];
-       file_t file;
-       char *rbuf = buf;
+  if (err)
+    goto out;
+  if (!S_ISLNK (st.st_mode))
+    {
+      err = EINVAL;
+      goto out;
+    }
 
-       err = __dir_lookup (file_stat, "", O_READ | O_NOLINK, 0, &doretry, retryname, &file);
-       if (! err && (doretry != FS_RETRY_NORMAL || retryname[0] != '\0'))
-         err = EGRATUITOUS;
-       if (! err)
-         {
-           err = __io_read (file, &rbuf, &len, 0, len);
-           if (!err && rbuf != buf)
-             {
-               memcpy (buf, rbuf, len);
-               __vm_deallocate (__mach_task_self (), (vm_address_t)rbuf, len);
-             }
+  err = __dir_lookup (file_stat, "", O_READ | O_NOLINK,
+                      0, &doretry, retryname, &file);
+  if (err)
+    goto out;
+  if (doretry != FS_RETRY_NORMAL || retryname[0] != '\0')
+    {
+      err = EGRATUITOUS;
+      goto out;
+    }
+
+  err = __io_read (file, &rbuf, &len, 0, len);
+  __mach_port_deallocate (__mach_task_self (), file);
+  if (err)
+    goto out;
+
+  if (rbuf != buf)
+    {
+      memcpy (buf, rbuf, len);
+      __vm_deallocate (__mach_task_self (), (vm_address_t) rbuf, len);
+    }
 
-           __mach_port_deallocate (__mach_task_self (), file);
-         }
-      }
-    else
-      err = EINVAL;
 
+ out:
   __mach_port_deallocate (__mach_task_self (), file_stat);
 
   return err ? __hurd_fail (err) : len;