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From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Max Reitz <mreitz@redhat.com>
Cc: virtio-fs@redhat.com
Subject: Re: [Virtio-fs] [RFC] Duplicate submounts in the guest
Date: Wed, 6 May 2020 16:52:12 +0100	[thread overview]
Message-ID: <20200506155212.GN2743@work-vm> (raw)
In-Reply-To: <20200506153258.238687-1-mreitz@redhat.com>

* Max Reitz (mreitz@redhat.com) wrote:
> Hi,
> 
> This RFC consists of two patch series, one for virtiofsd (i.e., to be
> applied to the qemu repo), and one for Linux.
> 
> The problem it wants to solve is that virtiofsd just passes through the
> stat.st_ino value from the host to the guest, without taking stat.st_dev
> into account.  Therefore, it is generally impossible to uniquely
> identify nodes in the guest by their st_dev/st_ino combinations.
> 
> One way to fix this would be to derive some algorithm to derive a unique
> st_ino value from the st_dev/st_ino combination on the host, but this is
> not always possible.
> 
> So what this series does it basically passing through st_dev alongside
> st_ino: We can let the guest create auto-mounted submounts for every
> host mount point, so that they get their own dedicated st_dev.  This is
> similar to what NFS does with the crossmnt option.

Nice;  this should probably get cc'd to fuse-devel and/or put as a pull
into their github to see what they have to say.

Dave

> Announcing submounts to the guest (the FUSE client) is done by the FUSE
> server (virtiofsd) of setting st_rdev to a non-zero value (e.g. st_dev)
> for every mount point.
> 
> In this version here, duplicate mounts on the host (same st_dev) will
> not necessarily have the same st_dev in the guest.  That would be more
> complicated to implement, and there is probably no real need to.
> 
> Furthermore, note that virtiofsd identifies files based on
> st_dev/st_ino, so if you do have duplicate mounts on the guest, it is
> very much possible that you will run into problems when trying to pass
> them through to the guest (because virtiofsd may treat them as one and
> the same tree).
> 
> -- 
> 2.26.2
> 
> _______________________________________________
> Virtio-fs mailing list
> Virtio-fs@redhat.com
> https://www.redhat.com/mailman/listinfo/virtio-fs
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK


  parent reply	other threads:[~2020-05-06 15:52 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-06 15:32 [Virtio-fs] [RFC] Duplicate submounts in the guest Max Reitz
2020-05-06 15:35 ` [Virtio-fs] [RFC 0/5] fuse: Auto-mounted submounts Max Reitz
2020-05-06 15:36   ` [Virtio-fs] [RFC 1/5] fuse: Store fuse_conn in fuse_req Max Reitz
2020-05-06 15:36   ` [Virtio-fs] [RFC 2/5] fuse: Drop fuse_conn parameter where possible Max Reitz
2020-05-06 15:36   ` [Virtio-fs] [RFC 3/5] fuse: Split fuse_mount off of fuse_conn Max Reitz
2020-05-07  9:56     ` Miklos Szeredi
2020-05-07 11:16       ` Max Reitz
2020-05-07 11:24         ` Miklos Szeredi
2020-05-07 12:07           ` Max Reitz
2020-05-07 14:05             ` Miklos Szeredi
2020-05-07 15:05               ` Max Reitz
2020-05-07 15:19                 ` Miklos Szeredi
2020-05-06 15:36   ` [Virtio-fs] [RFC 4/5] fuse: Allow fuse_fill_super_common() for submounts Max Reitz
2020-05-06 15:36   ` [Virtio-fs] [RFC 5/5] fuse: Implement crossmounts Max Reitz
2020-05-06 15:38 ` [Virtio-fs] [RFC 0/2] virtiofsd: Announce submounts Max Reitz
2020-05-06 15:40   ` [Virtio-fs] [RFC 1/2] virtiofsd: Store every lo_inode's parent_dev Max Reitz
2020-05-06 15:40   ` [Virtio-fs] [RFC 2/2] virtiofsd: Set st_rdev for sub-mount points Max Reitz
2020-05-06 16:04     ` Dr. David Alan Gilbert
2020-05-07 10:56       ` Max Reitz
2020-05-07 11:43         ` Miklos Szeredi
2020-05-07 12:18           ` Max Reitz
2020-05-07 13:06             ` Dr. David Alan Gilbert
2020-05-07 14:29             ` Miklos Szeredi
2020-05-07 15:15               ` Max Reitz
2020-05-07 15:23                 ` Miklos Szeredi
2020-05-06 15:52 ` Dr. David Alan Gilbert [this message]
2020-05-07 10:50   ` [Virtio-fs] [RFC] Duplicate submounts in the guest Max Reitz
2020-05-07 20:53 ` Vivek Goyal
2020-05-08  7:31   ` Max Reitz

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