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Allow distinguishing between umount and abort #122

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Nikratio opened this issue Nov 23, 2016 · 3 comments
Open

Allow distinguishing between umount and abort #122

Nikratio opened this issue Nov 23, 2016 · 3 comments
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enhancement

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@Nikratio
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Currently, both a call to umount(2) and writing "1" to /sys/fs/fuse/connections/NNN/abort will put the /dev/fuse fd into the same state: reading from it returns ENODEV, and polling on it returns POLLERR.

This causes problems for filesystems that want to ensure that the mountpoint is free when they exit. If accessing the device fd gives the above errors, they have to do an additional check to determine if they still need to unmount the mountpoint. This is difficult to do without
race conditions (think of someone unmounting and immediately re-starting a new filesystem instance).
@Nikratio
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Discussion on linux-fsdevel: http://www.spinics.net/lists/linux-fsdevel/msg104665.html

mscherer pushed a commit to gluster/glusterfs that referenced this issue May 23, 2017
@csabahenk @ShyamsundarR
fuse: implement "-oauto_unmount"
461888b 
libfuse has an auto_unmount option which,
if enabled, ensures that the file system
is unmounted at FUSE server termination
by running a separate monitor process
that performs the unmount when that
occurs. (This feature would probably
better be called "robust auto-unmount",
as FUSE servers usually do try to unmount
their file systems upon termination,
it's just this mechanism is not crash
resilient.)

This change implements that option and
behavior for glusterfs.

Note that "auto unmount" (robust or not) is
a leaky abstraction, as the kernel cannot
guarantee that at the path where the FUSE
fs is mounted is actually the toplevel mount
at the time of the umount(2) call, for
multiple reasons, among others, see:

  fuse-devel: "fuse: feasible to distinguish between umount and abort?"
  http://fuse.996288.n3.nabble.com/fuse-feasible-to-distinguish-between-umount-and-abort-tt14358.html
  libfuse/libfuse#122

Updates #153

Change-Id: Ia4432580c9fd2c156d9c73c3a44f4bfd42437599
Signed-off-by: Csaba Henk <csaba@redhat.com>
Reviewed-on: https://review.gluster.org/17230
Tested-by: Amar Tumballi <amarts@redhat.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
mscherer pushed a commit to gluster/glusterfs that referenced this issue Jun 20, 2017
@csabahenk @ShyamsundarR
fuse: implement "-oauto_unmount"
cd5c913 
libfuse has an auto_unmount option which,
if enabled, ensures that the file system
is unmounted at FUSE server termination
by running a separate monitor process
that performs the unmount when that
occurs. (This feature would probably
better be called "robust auto-unmount",
as FUSE servers usually do try to unmount
their file systems upon termination,
it's just this mechanism is not crash
resilient.)

This change implements that option and
behavior for glusterfs.

Note that "auto unmount" (robust or not) is
a leaky abstraction, as the kernel cannot
guarantee that at the path where the FUSE
fs is mounted is actually the toplevel mount
at the time of the umount(2) call, for
multiple reasons, among others, see:

  fuse-devel: "fuse: feasible to distinguish between umount and abort?"
  http://fuse.996288.n3.nabble.com/fuse-feasible-to-distinguish-between-umount-and-abort-tt14358.html
  libfuse/libfuse#122

Updates #153

> Change-Id: Ia4432580c9fd2c156d9c73c3a44f4bfd42437599
> Signed-off-by: Csaba Henk <csaba@redhat.com>
> Reviewed-on: https://review.gluster.org/17230
> Tested-by: Amar Tumballi <amarts@redhat.com>
> CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
> Smoke: Gluster Build System <jenkins@build.gluster.org>
> Reviewed-by: Amar Tumballi <amarts@redhat.com>
> NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
(cherry picked from commit 461888b)

Change-Id: Ia4432580c9fd2c156d9c73c3a44f4bfd42437599
Signed-off-by: Csaba Henk <csaba@redhat.com>
Reviewed-on: https://review.gluster.org/17573
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Amar Tumballi <amarts@redhat.com>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
amarts pushed a commit to amarts/glusterfs_fork that referenced this issue Oct 31, 2017
@csabahenk @amarts
fuse: implement "-oauto_unmount"
f433e1a 
libfuse has an auto_unmount option which,
if enabled, ensures that the file system
is unmounted at FUSE server termination
by running a separate monitor process
that performs the unmount when that
occurs. (This feature would probably
better be called "robust auto-unmount",
as FUSE servers usually do try to unmount
their file systems upon termination,
it's just this mechanism is not crash
resilient.)

This change implements that option and
behavior for glusterfs.

Note that "auto unmount" (robust or not) is
a leaky abstraction, as the kernel cannot
guarantee that at the path where the FUSE
fs is mounted is actually the toplevel mount
at the time of the umount(2) call, for
multiple reasons, among others, see:

  fuse-devel: "fuse: feasible to distinguish between umount and abort?"
  http://fuse.996288.n3.nabble.com/fuse-feasible-to-distinguish-between-umount-and-abort-tt14358.html
  libfuse/libfuse#122

Updates gluster#153

Change-Id: Ia4432580c9fd2c156d9c73c3a44f4bfd42437599
Signed-off-by: Csaba Henk <csaba@redhat.com>
Reviewed-on: https://review.gluster.org/17230
Tested-by: Amar Tumballi <amarts@redhat.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
@szmi
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szmi commented Jul 26, 2018

Should be fixed in upcoming 4.18:
commit 3b7008b226f3 fuse: return -ECONNABORTED on /dev/fuse read after abort

@Nikratio
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Nice!

@Nikratio Nikratio removed the kernel label Jul 27, 2018
@Nikratio Nikratio changed the title Filesystems cannot distinguish between umount and abort Allow distinguishing between umount and abort Jul 27, 2018
csabahenk added a commit to csabahenk/glusterfs that referenced this issue Mar 7, 2023
@csabahenk
fuse: implement "-oauto_unmount"
f859f28 
libfuse has an auto_unmount option which,
if enabled, ensures that the file system
is unmounted at FUSE server termination
by running a separate monitor process
that performs the unmount when that
occurs. (This feature would probably
better be called "robust auto-unmount",
as FUSE servers usually do try to unmount
their file systems upon termination,
it's just this mechanism is not crash
resilient.)

This change implements that option and
behavior for glusterfs.

Note that "auto unmount" (robust or not) is
a leaky abstraction, as the kernel cannot
guarantee that at the path where the FUSE
fs is mounted is actually the toplevel mount
at the time of the umount(2) call, for
multiple reasons, among others, see:

  fuse-devel: "fuse: feasible to distinguish between umount and abort?"
  http://fuse.996288.n3.nabble.com/fuse-feasible-to-distinguish-between-umount-and-abort-tt14358.html
  libfuse/libfuse#122

Updates gluster#153

> Change-Id: Ia4432580c9fd2c156d9c73c3a44f4bfd42437599
> Signed-off-by: Csaba Henk <csaba@redhat.com>
> Reviewed-on: https://review.gluster.org/17230
> Tested-by: Amar Tumballi <amarts@redhat.com>
> CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
> Smoke: Gluster Build System <jenkins@build.gluster.org>
> Reviewed-by: Amar Tumballi <amarts@redhat.com>
> NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
(cherry picked from commit 461888b)

Change-Id: Ia4432580c9fd2c156d9c73c3a44f4bfd42437599
Signed-off-by: Csaba Henk <csaba@redhat.com>
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@Nikratio @szmi