Message-ID: <CAEivzxf2qH8XBXA2a+U4bQeeVC+eB8m9tDC08jxT=trFEzLpTA@mail.gmail.com>
Date: Fri, 16 Aug 2024 10:58:21 +0200
From: Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To: Christian Brauner <brauner@...nel.org>
Cc: mszeredi@...hat.com, stgraber@...raber.org, linux-fsdevel@...r.kernel.org, 
	Seth Forshee <sforshee@...nel.org>, Miklos Szeredi <miklos@...redi.hu>, Vivek Goyal <vgoyal@...hat.com>, 
	German Maglione <gmaglione@...hat.com>, Amir Goldstein <amir73il@...il.com>, 
	Bernd Schubert <bschubert@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/11] fuse: basic support for idmapped mounts

On Fri, Aug 16, 2024 at 10:02 AM Christian Brauner <brauner@...nel.org> wrote:
>
> On Thu, Aug 15, 2024 at 11:24:17AM GMT, Alexander Mikhalitsyn wrote:
> > Dear friends,
> >
> > This patch series aimed to provide support for idmapped mounts
> > for fuse & virtiofs. We already have idmapped mounts support for almost all
> > widely-used filesystems:
> > * local (ext4, btrfs, xfs, fat, vfat, ntfs3, squashfs, f2fs, erofs, ZFS (out-of-tree))
> > * network (ceph)
> >
> > Git tree (based on torvalds/master):
> > v3: https://github.com/mihalicyn/linux/commits/fuse_idmapped_mounts.v3
> > current: https://github.com/mihalicyn/linux/commits/fuse_idmapped_mounts
> >
> > Changelog for version 3:
> > - introduce and use a new SB_I_NOIDMAP flag (suggested by Christian)
> > - add support for virtiofs (+user space virtiofsd conversion)
> >
> > Changelog for version 2:
> > - removed "fs/namespace: introduce fs_type->allow_idmap hook" and simplified logic
> > to return -EIO if a fuse daemon does not support idmapped mounts (suggested
> > by Christian Brauner)
> > - passed an "idmap" in more cases even when it's not necessary to simplify things (suggested
> > by Christian Brauner)
> > - take ->rename() RENAME_WHITEOUT into account and forbid it for idmapped mount case
> >
> > Links to previous versions:
> > v2: https://lore.kernel.org/linux-fsdevel/20240814114034.113953-1-aleksandr.mikhalitsyn@canonical.com
> > tree: https://github.com/mihalicyn/linux/commits/fuse_idmapped_mounts.v2
> > v1: https://lore.kernel.org/all/20240108120824.122178-1-aleksandr.mikhalitsyn@canonical.com/#r
> > tree: https://github.com/mihalicyn/linux/commits/fuse_idmapped_mounts.v1
> >
> > Having fuse (+virtiofs) supported looks like a good next step. At the same time
> > fuse conceptually close to the network filesystems and supporting it is
> > a quite challenging task.
> >
> > Let me briefly explain what was done in this series and which obstacles we have.
> >
> > With this series, you can use idmapped mounts with fuse if the following
> > conditions are met:
> > 1. The filesystem daemon declares idmap support (new FUSE_INIT response feature
> > flags FUSE_OWNER_UID_GID_EXT and FUSE_ALLOW_IDMAP)
> > 2. The filesystem superblock was mounted with the "default_permissions" parameter
> > 3. The filesystem fuse daemon does not perform any UID/GID-based checks internally
> > and fully trusts the kernel to do that (yes, it's almost the same as 2.)
> >
> > I have prepared a bunch of real-world examples of the user space modifications
> > that can be done to use this extension:
> > - libfuse support
> > https://github.com/mihalicyn/libfuse/commits/idmap_support
> > - fuse-overlayfs support:
> > https://github.com/mihalicyn/fuse-overlayfs/commits/idmap_support
> > - cephfs-fuse conversion example
> > https://github.com/mihalicyn/ceph/commits/fuse_idmap
> > - glusterfs conversion example (there is a conceptual issue)
> > https://github.com/mihalicyn/glusterfs/commits/fuse_idmap
> > - virtiofsd conversion example
> > https://gitlab.com/virtio-fs/virtiofsd/-/merge_requests/245
>
> So I have no further comments on this and from my perspective this is:
>
> Reviewed-by: Christian Brauner <brauner@...nel.org>

Thanks, Christian! ;-)

>
> I would really like to see tests for this feature as this is available
> to unprivileged users.

Sure. I can confirm that this thing passes xfstests for virtiofs.

My setup:

- host machine

Virtiofsd options:

[ virtiofsd sources from
https://gitlab.com/virtio-fs/virtiofsd/-/merge_requests/245 ]
./target/debug/virtiofsd --socket-path=/tmp/vfsd.sock --shared-dir
/home/alex/Documents/dev/tmp --announce-submounts
--inode-file-handles=mandatory --posix-acl

QEMU options:
        -object memory-backend-memfd,id=mem,size=$RAM,share=on \
        -numa node,memdev=mem \
        -chardev socket,id=char0,path=/tmp/vfsd.sock \
        -device vhost-user-fs-pci,queue-size=1024,chardev=char0,tag=myfs \

- guest

xfstests version:

root@...ntu:/home/ubuntu/xfstests-dev# git log | head -n 3
commit f5ada754d5838d29fd270257003d0d123a9d1cd2
Author: Darrick J. Wong <djwong@...nel.org>
Date:   Fri Jul 26 09:51:07 2024 -0700

root@...ntu:/home/ubuntu/xfstests-dev# cat local.config
export TEST_DEV=myfs
export TEST_DIR=/mnt/test
export FSTYP=virtiofs

root@...ntu:/home/ubuntu/xfstests-dev# ./check -g idmapped
FSTYP         -- virtiofs
PLATFORM      -- Linux/x86_64 ubuntu 6.11.0-rc3+ #2 SMP
PREEMPT_DYNAMIC Fri Aug 16 10:23:41 CEST 2024

generic/633 1s ...  0s
generic/644 0s ...  1s
generic/645 18s ...  18s
generic/656       [not run] fsgqa user not defined.
generic/689       [not run] fsgqa user not defined.
generic/696       [not run] this test requires a valid $SCRATCH_DEV
generic/697 0s ...  1s
generic/698       [not run] this test requires a valid $SCRATCH_DEV
generic/699       [not run] this test requires a valid $SCRATCH_DEV
Ran: generic/633 generic/644 generic/645 generic/656 generic/689
generic/696 generic/697 generic/698 generic/699
Not run: generic/656 generic/689 generic/696 generic/698 generic/699
Passed all 9 tests

I'll try to do more tests, for example with fuse-overlayfs and get
back with results.

Kind regards,
Alex

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