Avoid readlink syscalls when reading derivations

strace -c reports over 10,000 readlink syscalls when reading the derivation
for the hello package. By just setting the %file-port-name-canonicalization
fluid, this drops to less than 10.

I'm not sure if this actually improves performance, but doing less is surely
better.

1 files changed, 6 insertions, 2 deletions

diff --git a/guix-build-coordinator/utils.scm b/guix-build-coordinator/utils.scm
index fdd7ee3..1d5ddbd 100644
--- a/guix-build-coordinator/utils.scm
+++ b/guix-build-coordinator/utils.scm
@@ -474,8 +474,12 @@ context."
                  ;; avoid having many open files when reading a derivation with
                  ;; inputs, read it in to a string first.
                  (call-with-input-string
-                     (call-with-input-file file
-                       get-string-all)
+                     ;; Avoid calling scm_i_relativize_path in
+                     ;; fport_canonicalize_filename since this leads to lots
+                     ;; of readlink calls
+                     (with-fluids ((%file-port-name-canonicalization 'none))
+                       (call-with-input-file file
+                         get-string-all))
                    (lambda (port)
                      (set-port-filename! port file)
                      (read-derivation port read-derivation-from-file*)))))