From 461064da9e169df3dd939b734bb2860598d113f4 Mon Sep 17 00:00:00 2001
From: Caleb Ristvedt <caleb.ristvedt@cune.org>
Date: Wed, 24 Jun 2020 00:56:50 -0500
Subject: [PATCH 1/2] deduplication: retry on ENOENT.

It's possible for the garbage collector to remove the "canonical" link after
it's been detected as existing by 'deduplicate'.  This would cause an ENOENT
error when replace-with-link attempts to create the temporary link.  This
changes it so that it will properly handle that by retrying.

* guix/store/deduplication.scm (deduplicate): retry on ENOENT.
---
 guix/store/deduplication.scm | 64 +++++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 23 deletions(-)

diff --git a/guix/store/deduplication.scm b/guix/store/deduplication.scm
index 6784ee0b92..b6d94e49c2 100644
--- a/guix/store/deduplication.scm
+++ b/guix/store/deduplication.scm
@@ -161,26 +161,44 @@ under STORE."
                   (scandir* path))
         (let ((link-file (string-append links-directory "/"
                                         (bytevector->nix-base32-string hash))))
-          (if (file-exists? link-file)
-              (replace-with-link link-file path
-                                 #:swap-directory links-directory)
-              (catch 'system-error
-                (lambda ()
-                  (link path link-file))
-                (lambda args
-                  (let ((errno (system-error-errno args)))
-                    (cond ((= errno EEXIST)
-                           ;; Someone else put an entry for PATH in
-                           ;; LINKS-DIRECTORY before we could.  Let's use it.
-                           (replace-with-link path link-file
-                                              #:swap-directory links-directory))
-                          ((= errno ENOSPC)
-                           ;; There's not enough room in the directory index for
-                           ;; more entries in .links, but that's fine: we can
-                           ;; just stop.
-                           #f)
-                          ((= errno EMLINK)
-                           ;; PATH has reached the maximum number of links, but
-                           ;; that's OK: we just can't deduplicate it more.
-                           #f)
-                          (else (apply throw args)))))))))))
+          (let retry ()
+            (if (file-exists? link-file)
+                (catch 'system-error
+                  (lambda ()
+                    (replace-with-link link-file path
+                                       #:swap-directory links-directory))
+                  (lambda args
+                    (if (and (= (system-error-errno args) ENOENT)
+                             ;; ENOENT can be produced because:
+                             ;; - LINK-FILE has missing directory components
+                             ;; - LINKS-DIRECTORY has missing directory
+                             ;;   components
+                             ;; - PATH has missing directory components
+                             ;;
+                             ;; the last two are errors, the first just
+                             ;; requires a retry.
+                             (file-exists? (dirname path))
+                             (file-exists? links-directory))
+                        (retry)
+                        (apply throw args))))
+                (catch 'system-error
+                  (lambda ()
+                    (link path link-file))
+                  (lambda args
+                    (let ((errno (system-error-errno args)))
+                      (cond ((= errno EEXIST)
+                             ;; Someone else put an entry for PATH in
+                             ;; LINKS-DIRECTORY before we could.  Let's use
+                             ;; it.
+                             (retry))
+                            ((= errno ENOSPC)
+                             ;; There's not enough room in the directory index
+                             ;; for more entries in .links, but that's fine:
+                             ;; we can just stop.
+                             #f)
+                            ((= errno EMLINK)
+                             ;; PATH has reached the maximum number of links,
+                             ;; but that's OK: we just can't deduplicate it
+                             ;; more.
+                             #f)
+                            (else (apply throw args))))))))))))
-- 
2.26.2