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Re: [PATCH 1/3] virtiofsd: Find original inode ID of mount points
From: |
Connor Kuehl |
Subject: |
Re: [PATCH 1/3] virtiofsd: Find original inode ID of mount points |
Date: |
Wed, 12 May 2021 10:59:28 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 |
On 5/12/21 7:55 AM, Max Reitz wrote:
> Mount point directories represent two inodes: On one hand, they are a
> normal directory on their parent filesystem. On the other, they are
> the
> root node of the filesystem mounted there. Thus, they have two inode
> IDs.
>
> Right now, we only report the latter inode ID (i.e. the inode ID of
> the
> mounted filesystem's root node). This is fine once the guest has
> auto-mounted a submount there (so this inode ID goes with a device ID
> that is distinct from the parent filesystem), but before the
> auto-mount,
> they have the device ID of the parent and the inode ID for the
> submount.
> This is problematic because this is likely exactly the same
> st_dev/st_ino combination as the parent filesystem's root node. This
> leads to problems for example with `find`, which will thus complain
> about a filesystem loop if it has visited the parent filesystem's root
> node before, and then refuse to descend into the submount.
>
> There is a way to find the mount directory's original inode ID, and
> that
> is to readdir(3) the parent directory, look for the mount directory,
> and
> read the dirent.d_ino field. Using this, we can let lookup and
> readdirplus return that original inode ID, which the guest will thus
> show until the submount is auto-mounted. (Then, it will invoke
> getattr
> and that stat(2) call will return the inode ID for the submount.)
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
This is a clever way of uncovering the inode ID.
Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
[PATCH 2/3] virtiofs_submounts.py: Do not generate ssh key, Max Reitz, 2021/05/12
[PATCH 3/3] virtiofs_submounts.py: Check `find`, Max Reitz, 2021/05/12