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From:   NeilBrown <neilb@suse.de>
To:     Craig Small <csmall@dropbear.xyz>, linux-nfs@vger.kernel.org
Date:   Thu, 21 May 2020 15:12:49 +1000
Subject: Re: How to separate NFS mounts have same device ID
In-Reply-To: <20200521023055.GA1246587@dropbear.xyz>
References: <20200521023055.GA1246587@dropbear.xyz>
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On Thu, May 21 2020, Craig Small wrote:

> Hi,
>   I'm the author of the psmisc programs that include things like killall and fuser.  I have a problem with finding files open on NFS mounts from the same server.  The issue is at https://gitlab.com/psmisc/psmisc/-/issues/10
>
> The way fuser does its job is to find the mounts you specify and collect the device IDs, then scans all /proc/<PID/fd/* for matching devices. However, NFS mounts from the same server have the same device ID so fuser reports every mount has the same file opened.
>
> Putting it another way, if I said "here is file /proc/<PID>/fd/3, dereference the symlink and tell me which of these two NFS mounts from the same server it comes from?" how would you do it?
> A simple string match (/mnt/a vs /mnt/b) does not work because you can have symlinks across mounts.

I would examine /proc/<PID>/fdinfo/3 and extract the 'mnt_id:' number,
then look for that (as the first field) in /proc/<PID>/mountinfo.

NeilBrown


>
> Any help here would be appreciated. I'm not subscribed to the list so hopefully, this makes it through whatever filters there are and please CC me on replies.
>
>  - Craig

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