gnu: system: file-systems: Add shared flag.

* gnu/build/file-systems.scm (mount-flags->bit-mask, mount-file-system):
Handle shared flag.
* gnu/system/file-systems.scm (invalid-file-system-flags): Add shared to known
flags.
* guix/build/syscalls.scm (MS_SHARED): New variable.
* doc/guix.texi (File Systems): Document shared flag.

4 files changed, 15 insertions, 3 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index eb3a1a4eb5..99321929cc 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -16421,8 +16421,9 @@ include @code{read-only}, @code{bind-mount}, @code{no-dev} (disallow
 access to special files), @code{no-suid} (ignore setuid and setgid
 bits), @code{no-atime} (do not update file access times),
 @code{strict-atime} (update file access time), @code{lazy-time} (only
-update time on the in-memory version of the file inode), and
-@code{no-exec} (disallow program execution).
+update time on the in-memory version of the file inode),
+@code{no-exec} (disallow program execution), and @code{shared} (make the
+mount shared).
 @xref{Mount-Unmount-Remount,,, libc, The GNU C Library Reference
 Manual}, for more information on these flags.
 
diff --git a/gnu/build/file-systems.scm b/gnu/build/file-systems.scm
index 1d3b33e7bd..b9d46c9350 100644
--- a/gnu/build/file-systems.scm
+++ b/gnu/build/file-systems.scm
@@ -6,6 +6,7 @@
 ;;; Copyright © 2019–2021 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;; Copyright © 2019 David C. Trudgian <dave@trudgian.net>
 ;;; Copyright © 2020 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;; Copyright © 2022 Oleg Pykhalov <go.wigust@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -1123,6 +1124,8 @@ corresponds to the symbols listed in FLAGS."
        (logior MS_STRICTATIME (loop rest)))
       (('lazy-time rest ...)
        (logior MS_LAZYTIME (loop rest)))
+      (('shared rest ...)
+       (loop rest))
       (()
        0))))
 
@@ -1186,6 +1189,9 @@ corresponds to the symbols listed in FLAGS."
         (cond
          ((string-prefix? "nfs" type)
           (mount-nfs source target type flags options))
+         ((memq 'shared (file-system-flags fs))
+          (mount source target type flags options)
+          (mount "none" target #f MS_SHARED))
          (else
           (mount source target type flags options)))
 
diff --git a/gnu/system/file-systems.scm b/gnu/system/file-systems.scm
index f8f4276283..464b76a2ca 100644
--- a/gnu/system/file-systems.scm
+++ b/gnu/system/file-systems.scm
@@ -4,6 +4,7 @@
 ;;; Copyright © 2020 Jakub Kądziołka <kuba@kadziolka.net>
 ;;; Copyright © 2020, 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 ;;; Copyright © 2021 Tobias Geerinckx-Rice <me@tobias.gr>
+;;; Copyright © 2022 Oleg Pykhalov <go.wigust@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -121,7 +122,8 @@
     ;; Note: Keep in sync with 'mount-flags->bit-mask'.
     (let ((known-flags '(read-only
                          bind-mount no-suid no-dev no-exec
-                         no-atime strict-atime lazy-time)))
+                         no-atime strict-atime lazy-time
+                         shared)))
       (lambda (flags)
         "Return the subset of FLAGS that is invalid."
         (remove (cut memq <> known-flags) flags))))
diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index a7401fd73f..eda487f52e 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -8,6 +8,7 @@
 ;;; Copyright © 2020 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2021 Chris Marusich <cmmarusich@gmail.com>
 ;;; Copyright © 2021 Tobias Geerinckx-Rice <me@tobias.gr>
+;;; Copyright © 2022 Oleg Pykhalov <go.wigust@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -49,6 +50,7 @@
             MS_RELATIME
             MS_BIND
             MS_MOVE
+            MS_SHARED
             MS_LAZYTIME
             MNT_FORCE
             MNT_DETACH
@@ -537,6 +539,7 @@ the last argument of `mknod'."
 (define MS_NOATIME         1024)
 (define MS_BIND            4096)
 (define MS_MOVE            8192)
+(define MS_SHARED       1048576)
 (define MS_RELATIME     2097152)
 (define MS_STRICTATIME 16777216)
 (define MS_LAZYTIME    33554432)