[PATCH] build: file-systems: Allow for bind mounting regular files.

[David Thompson]

As I was working on my container implementation I noticed that
'mount-file-system' doesn't support bind mounting regular files because
it assumes that all mount points are directories.  This patch fixes
that.

>From f94fec6cde3826f20c0d69a45c2aa1928c1d0a78 Mon Sep 17 00:00:00 2001
From: David Thompson <address@hidden>
Date: Sat, 1 Aug 2015 13:43:33 -0400
Subject: [PATCH] build: file-systems: Allow for bind mounting regular files.

* gnu/build/file-systems.scm (regular-file?): New procedure.
  (mount-file-system): Create a regular file instead of a directory when bind
  mounting a regular file.
---
 gnu/build/file-systems.scm | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/gnu/build/file-systems.scm b/gnu/build/file-systems.scm
index c58d23c..f0d6f70 100644
--- a/gnu/build/file-systems.scm
+++ b/gnu/build/file-systems.scm
@@ -305,6 +305,10 @@ the following:
                fsck code device)
        (start-repl)))))
 
+(define (regular-file? file-name)
+  "Return #t if FILE-NAME is a regular file."
+  (eq? (stat:type (stat file-name)) 'regular))
+
 (define (mount-flags->bit-mask flags)
   "Return the number suitable for the 'flags' argument of 'mount' that
 corresponds to the symbols listed in FLAGS."
@@ -339,7 +343,16 @@ run a file system check."
            (flags       (mount-flags->bit-mask flags)))
        (when check?
          (check-file-system source type))
-       (mkdir-p mount-point)
+
+       ;; Create the mount point.  Most of the time this is a directory, but
+       ;; in the case of a bind mount, a regular file may be needed.
+       (if (and (= MS_BIND (logand flags MS_BIND))
+                (regular-file? source))
+           (begin
+             (mkdir-p (dirname mount-point))
+             (call-with-output-file mount-point (const #t)))
+           (mkdir-p mount-point))
+
        (mount source mount-point type flags options)
 
        ;; For read-only bind mounts, an extra remount is needed, as per
-- 
2.4.3

-- 
David Thompson
GPG Key: 0FF1D807