Re: name_to_handle_at() and persistent filesystem IDs

From: Michael Kerrisk (man-pages)
Date: Mon Mar 17 2014 - 12:17:24 EST

Hello Aneesh,

On Sun, Mar 16, 2014 at 4:08 PM, Aneesh Kumar K.V
<aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
> Michael Kerrisk <mtk.manpages@xxxxxxxxx> writes:
>> Hello Aneesh,
>> I'm currently working on a man page for name_to_handle_at() and
>> open_by_handle_at(), and I have a question relating to a point that
>> probably needs to be covered in the man page.
>> Back in July 2010, in this thread:
>> you said:
>> [[
>> mount id should not be looked at as a persistent identifier. It should
>> be used to derive a persistent identifier from /proc/self/mountinfo. The
>> persistent identifier could be the combination of device properties,
>> file system properties or the uuid which is going to be an optional
>> tag in /proc/self/mountinfo.
>> ]]
>> In the man page, I'd like to briefly describe how one derives such a
>> persistent ID from mountinfo. AFAICS, the optional UUID tag in
>> /proc/self/mountinfo has not come to pass. So, what then is the
>> recommended practice for deriving the persistent ID?
> Anything that work for the application. mount_id will indicate which
> mount it is ie. from /proc/self/mountinfo
> 30 20 8:1 / /boot rw,relatime - ext4 /dev/sda1 rw,data=ordered
> The value 30 helps us to figure out that we are looking at device
> /dev/sda1. With that we can derive the uuid using libblkid. I am not sure we
> concluded anything really about how to identify an nfs mount. May be we
> can do that based on server and mount point details ?.But from the
> syscall point, what we return is mount_id, which gives a hint regarding
> which mount point we are talking about in /proc/self/mountinfo. From
> that information applications can use any method that work for them
> to derivce an unique identifier.
> I know that NFS ganesha use these syscall. May we can check with them
> what worked for them ? (Added to CC:)

Thanks, that helped, as as I hope is evident from the page I just sent.



Michael Kerrisk
Linux man-pages maintainer;
Linux/UNIX System Programming Training:
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