[bug#67238] [PATCH] derivations: Avoid readlink syscalls in read-derivation-from-file.

[Christopher Baines]

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.

* guix/derivations.scm (read-derivation-from-file): Set
%file-port-name-canonicalization to 'none when calling call-with-input-file.

Change-Id: I1ff16a059160576a576f2e9ed881379596e66af3
---
 guix/derivations.scm | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/guix/derivations.scm b/guix/derivations.scm
index 9fec7f4f0b..e6ecb570c4 100644
--- a/guix/derivations.scm
+++ b/guix/derivations.scm
@@ -556,7 +556,12 @@ (define (read-derivation-from-file file)
   ;; and because the same argument is read more than 15 times on average
   ;; during something like (package-derivation s gdb).
   (or (and file (hash-ref %derivation-cache file))
-      (let ((drv (call-with-input-file file read-derivation)))
+      (let ((drv
+             ;; 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 read-derivation))))
         (hash-set! %derivation-cache file drv)
         drv)))
 

base-commit: e35b7c5386c1bfacf47ed31bac9b503373dd26fc
-- 
2.41.0