[PATCH] shadow_copy2: Allow configurable prefix for snapshots

[Rajesh Joseph]

Hi all,

I would really appreciate if I get some review comments or better an ack on
this patch :-)

Thanks & regards,
Rajesh

On Mon, Apr 18, 2016 at 7:48 PM, Rajesh Joseph <rjoseph at redhat.com> wrote:

> Hi all,
>
> Current shadow_copy2 module provide a configurable time format
> (shadow:format) to specify snapshot names. But this seems little
> restrictive in nature where your snapshot name can only be a time string.
>
> I updated shadow_copy2 module to take a new prefix option. With this now
> user can also provide a configurable prefix along with time format.
>
> Implementation detail:
> Let's say the underlying file-system creates snapshots in the following
> format
> <snap_name>_GMT-%Y.%m.%d-%H.%M.%S
>
> Windows expect snapshot names to be in the following format
> @GMT-%Y.%m.%d-%H.%M.%S
>
> VFS using shadow_copy2 module converts underlying file-system format  to
> the Windows format and vice-versa.
>
> Earlier with just a time and the shadow:format you can create a unique
> file-name and access that file. With the addition of prefix this is no more
> valid. Now with given time we also need to find a unique file which will
> match the prefix.
>
> One way to address this is to scan the directory every time we access
> snapshot. Another way, which I have chosen, is to store the list of
> snapshot on the first scan and use this list for subsequent access.
>
> The implementation currently uses a global list to save the list of
> snapshot names so that we
> can get actual snapshot name with a given time-stamp. Currently I am using
> VFS handle's private
> variable to store this list.
>
> This approach was already discussed with Michael Adam (obnox) and Ira
> Cooper. I got some internal review comments from Ira, which I addressed.
>
> Ira also raised a question on this approach and how well it can work
> durable handles and persistent handles. I am saving or creating the
> snapshot list in shadow_copy2_get_shadow_copy_data function. Ira suspected
> that there is no guarantee shadow_copy2_get_shadow_copy_data function will
> be called before shadow_copy2_get_real_filename, and other routines like
> it. Especially in case of a reconnect.
>
> Since I am not very well versed with this part of code, I like to have
> opinion of others here.
>
> Also review the patch and let me know if you have any comments.
>
> Thanks & Regards,
> Rajesh
>