GNU bug report logs - #56880
[PATCH] gnu: system: file-systems: Add shared flag.

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Oleg Pykhalov <go.wigust <at> gmail.com>
Subject: bug#56880: closed (Re: bug#56880: [PATCH] gnu: system:
 file-systems: Add shared flag.)
Date: Wed, 10 Aug 2022 04:20:03 +0000

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Your bug report

#56880: [PATCH] gnu: system: file-systems: Add shared flag.

which was filed against the guix-patches package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 56880 <at> debbugs.gnu.org.

-- 
56880: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=56880
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Oleg Pykhalov <go.wigust <at> gmail.com>
To: Ludovic Courtès <ludo <at> gnu.org>
Cc: 56880-done <at> debbugs.gnu.org
Subject: Re: bug#56880: [PATCH] gnu: system: file-systems: Add shared flag.
Date: Wed, 10 Aug 2022 07:19:38 +0300

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Ludovic Courtès <ludo <at> gnu.org> writes:

[…]

>> I looked again on this procedure before merge.  With applied patch it
>> will return a wrong bitmask according to the manual page:
>>
>> mount(2)
>>
>>     The  only other flags that can be specified while changing the propaga‐
>>     tion type are MS_REC (described below)  and  MS_SILENT  (which  is  ig‐
>>     nored).
>>
>> Also I tried to invoke 'mount' from C code, if MS_SHARED specified and
>> mountpoint does not exist (not mounted without MS_SHARED before), then
>> nothing will happen.
>
> Hmm not sure I follow.

[…]

>> 2. Modify option-string->mount-flags in such way, that it will return
>> multiple bitmasks or in some other way.

[…]

> I’m not sure what option #2 means concretely?

We need to call mount(2) two times, which is not handled by
option-string->mount-flags which returns only one mount(2) bitmask.

I pushed #1 as 4b494878380920c8c7eecccd1f299164dd4a2c3f to master.


Oleg.

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From: Oleg Pykhalov <go.wigust <at> gmail.com>
To: guix-patches <at> gnu.org
Cc: Oleg Pykhalov <go.wigust <at> gmail.com>
Subject: [PATCH] gnu: system: file-systems: Add shared flag.
Date: Tue,  2 Aug 2022 14:23:09 +0300

* 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.
(option-string->mount-flags): Handle shared flag.
* doc/guix.texi (File Systems): Document shared flag.
---
 doc/guix.texi               | 5 +++--
 gnu/build/file-systems.scm  | 6 ++++++
 gnu/system/file-systems.scm | 4 +++-
 guix/build/syscalls.scm     | 6 +++++-
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 9d17050ffc..106ab428d9 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -16376,8 +16376,9 @@ 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 <at> tobias.gr>
 ;;; Copyright © 2019 David C. Trudgian <dave <at> trudgian.net>
 ;;; Copyright © 2020 Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
+;;; Copyright © 2022 Oleg Pykhalov <go.wigust <at> gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -1123,6 +1124,8 @@ (define (mount-flags->bit-mask flags)
        (logior MS_STRICTATIME (loop rest)))
       (('lazy-time rest ...)
        (logior MS_LAZYTIME (loop rest)))
+      (('shared rest ...)
+       (loop rest))
       (()
        0))))
 
@@ -1186,6 +1189,9 @@ (define (mount-nfs source mount-point type flags options)
         (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 <at> kadziolka.net>
 ;;; Copyright © 2020, 2021 Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
 ;;; Copyright © 2021 Tobias Geerinckx-Rice <me <at> tobias.gr>
+;;; Copyright © 2022 Oleg Pykhalov <go.wigust <at> gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -121,7 +122,8 @@ (define invalid-file-system-flags
     ;; 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..ef0b1d67fd 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -8,6 +8,7 @@
 ;;; Copyright © 2020 Jan (janneke) Nieuwenhuizen <janneke <at> gnu.org>
 ;;; Copyright © 2021 Chris Marusich <cmmarusich <at> gmail.com>
 ;;; Copyright © 2021 Tobias Geerinckx-Rice <me <at> tobias.gr>
+;;; Copyright © 2022 Oleg Pykhalov <go.wigust <at> gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -49,6 +50,7 @@ (define-module (guix build syscalls)
             MS_RELATIME
             MS_BIND
             MS_MOVE
+            MS_SHARED
             MS_LAZYTIME
             MNT_FORCE
             MNT_DETACH
@@ -537,6 +539,7 @@ (define MS_REMOUNT           32)
 (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)
@@ -637,7 +640,8 @@ (define lst
                         ("nodev"      => MS_NODEV)
                         ("noexec"     => MS_NOEXEC)
                         ("relatime"   => MS_RELATIME)
-                        ("noatime"    => MS_NOATIME)))))))
+                        ("noatime"    => MS_NOATIME)
+                        ("shared"     => MS_SHARED)))))))
 
 (define (mount-flags mount)
   "Return the mount flags of MOUNT, a <mount> record, as an inclusive or of
-- 
2.37.0

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