Re: How to know when a fuse filesystem is properly unmounted

[songbird <songbird@anthive.com>]

Tim Woodall wrote:
> Short script below that shows my problem.
>
> fusermount -u (and umount) both return before all the data is written 
> out to the backing file on a fuse FS. Is there any way to tell when this 
> is complete? I tried running fuse in the foreground and then doing a 
> wait $PID but that didn't help, I still needed the sleep.
>
> At least on my system, with a fs of 50G it always unmounts quickly 
> enough for the e2fsck to pass, at 500G it sometimes does, and at 5T it 
> seems to always fail without the sleep (which can probably be a bit 
> shorter than 30s but I haven't bothered to try to work out exactly how 
> much shorter it can safely be.
>
> Tim.
>
> #!/bin/bash
>
> set -e
>
> ROOT=mount
> DEV=container_mount/pv1
>
> rm -f container
> rm -fr container_mount
> rm -fr mount
>
> mkdir -p container_mount
>
> # create a container fs that can hold a 5T sparse file
> truncate -s 3G container
> /sbin/mke2fs -t ext4 -O \
>    none,has_journal,ext_attr,dir_index,filetype,extent,64bit,flex_bg,sparse_super,large_file,huge_file,dir_nlink,extra_is
>    -b 4096 container
>
> fuse2fs -o fakeroot container container_mount
>
> mkdir -p "$ROOT"
>
> echo "truncate $(date)"
> truncate -s 5T "${DEV}"
>
> echo "mke2fs $(date)"
> /sbin/mkfs.ext4 -N 1000000 -O \
>    none,has_journal,ext_attr,dir_index,filetype,extent,64bit,flex_bg,sparse_super,large_file,huge_file,dir_nlink,extra_is
>    -b 1024 "$DEV"
>
> echo "fuse2fs ${DEV} ${ROOT} $(date)"
> fuse2fs -o fakeroot "$DEV" "$ROOT"
>
> echo "make filler $(date)"
> touch "${ROOT}/filler"
> echo "fusermount -u $ROOT $(date)"
> fusermount -u "$ROOT"
>
> ### How can I avoid this step
> echo "sleeping"
> sleep 30
>
> /sbin/e2fsck -f "$DEV" || true
>
> fusermount -u container_mount
> rm container
> rmdir $ROOT
> rmdir container_mount
>
> exit 0
>
>


  sync should do it, but there are important details to check
which i hope are explained by the man page or the referenced
items at the bottom:


"BUGS
       Persistence guarantees vary per system.  See the system calls below  for
       more details.

AUTHOR
       Written by Jim Meyering and Giuseppe Scrivano.

REPORTING BUGS
       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
       Report any translation bugs to <https://translationproject.org/team/>

SEE ALSO
       fdatasync(2), fsync(2), sync(2), syncfs(2)

       Full documentation <https://www.gnu.org/software/coreutils/sync>
       or available locally via: info '(coreutils) sync invocation'
"

  songbird