GNU bug report logs - #37884
27.0.50; Cannot write to a file in VirtualBox shared directory

Previous Next

Full log

View this message in rfc822 format

From: Robert Pluim <rpluim <at> gmail.com>
To: Bernardo <bernardo.bacic <at> pobox.com>
Cc: 37884 <at> debbugs.gnu.org
Subject: bug#37884: 27.0.50; Cannot write to a file in VirtualBox shared directory
Date: Thu, 24 Oct 2019 18:10:59 +0200

>>>>> On Wed, 23 Oct 2019 21:28:06 +1100, Bernardo <bernardo.bacic <at> pobox.com> said:

    Bernardo> When Emacs is started with strace ( $ strace emacs -Q ) it can be seen
    Bernardo> that there are issues with the lock file that's created -
    Bernardo> /media/sf_Home/.#zz_stuff

    Bernardo> The strace messages are in the attachement.

Weʼre getting EPERM when doing unlink on the lock file, which is very
strange.

    Bernardo> The 'shared directory' is a feature of Virtual Box which allows both the
    Bernardo> host and applications running in a virtual machine to have access to
    Bernardo> files in the same directory.

    Bernardo> The file system type of the shared directory is vboxsf which seems to be
    Bernardo> a layer on top of NTFS.
    Bernardo>   $ mount | grep vbox
    Bernardo>   Home on /media/sf_Home type vboxsf (rw,nodev,relatime,<snip>

    Bernardo> It looks like symbolic links are not allowed on
    Bernardo> this FS type; from terminal:
    Bernardo>   $ ln -s zz_stuff my_link
    Bernardo>   ln: failed to create symbolic link 'my_link': Operation not permitted

Right, so emacs switches to a regular file instead:

symlink fails:
    symlink("mk7 <at> deb.2246:1571819801", "/media/sf_Home/.#zz_stuff") = -1 EPERM (Operation not permitted)

so use a regular file:

    open("/media/sf_Home/.#-emacsvxLcB2", O_RDWR|O_CREAT|O_EXCL|O_CLOEXEC, 0600) = 13

and put the lock information inside the file, and make it read-only:

    write(13, "mk7 <at> deb.2246:1571819801", 23) = 23
    fchmod(13, 0444)                        = 0

and then rename it:

    "/media/sf_Home/.#zz_stuff", RENAME_NOREPLACE) = 0

Later on when emacs saves the file, it tries to get rid of the lock
file, which fails:

    unlink("/media/sf_Home/.#zz_stuff")     = -1 EPERM (Operation not permitted)

So your filesystem doesnʼt let you call unlink() on read-only files? I
guess we could try adjusting the chmod to 664 or similar if that helps here.

Robert

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.