readlink.2: srcfix: Note that bufsiz has a signed type at kernel level

So on a direct syscall, the EINVAL could also occur for bufsiz < 0.
But at the moment, the error text is sufficiently vague
("bufsiz is not positive") that a change to the man page text
is probably not needed.

man2/readlink.2

@@ -88,6 +88,11 @@ extends outside the process's allocated address space.
 .B EINVAL
 .I bufsiz
 is not positive.
+.\" At the glibc level, bufsiz is unsigned, so this error can only occur
+.\" if bufsiz==0.  However, the in the kernel syscall, bufsiz is signed,
+.\" and this error can also occur if bufsiz < 0.
+.\" See: http://thread.gmane.org/gmane.linux.man/380
+.\" Subject: [patch 0/3] [RFC] kernel/glibc mismatch of "readlink" syscall?
 .TP
 .B EINVAL
 The named file is not a symbolic link.