linux-kernel - Re: [RFC v2 09/16] luo: luo_files: implement file systems callbacks

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Message-ID: <mafs0h60jmzzc.fsf@kernel.org>
Date: Fri, 13 Jun 2025 17:18:47 +0200
From: Pratyush Yadav <pratyush@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: Re: [RFC v2 09/16] luo: luo_files: implement file systems callbacks

On Sun, Jun 08 2025, Pasha Tatashin wrote:

> On Thu, Jun 5, 2025 at 12:04 PM Pratyush Yadav <pratyush@...nel.org> wrote:
>>
>> On Thu, May 15 2025, Pasha Tatashin wrote:
>>
>> > Implements the core logic within luo_files.c to invoke the prepare,
>> > reboot, finish, and cancel callbacks for preserved file instances,
>> > replacing the previous stub implementations. It also handles
>> > the persistence and retrieval of the u64 data payload associated with
>> > each file via the LUO FDT.
>> >
>> > This completes the core mechanism enabling registered filesystem
>> > handlers to actively manage file state across the live update
>> > transition using the LUO framework.
>> >
>> > Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
>> > ---
>> >  drivers/misc/liveupdate/luo_files.c | 105 +++++++++++++++++++++++++++-
>> >  1 file changed, 103 insertions(+), 2 deletions(-)
>> >
>> [...]
>> > @@ -305,7 +369,29 @@ int luo_do_files_prepare_calls(void)
>> >   */
>> >  int luo_do_files_freeze_calls(void)
>> >  {
>> > -     return 0;
>> > +     unsigned long token;
>> > +     struct luo_file *h;
>> > +     int ret;
>> > +
>> > +     xa_for_each(&luo_files_xa_out, token, h) {
>>
>> Should we also ensure at this point that there are no open handles to
>> this file? How else would a file system ensure the file is in quiescent
>> state to do its final serialization?
>
> Do you mean check refcnt here? If so, this is a good idea, but first
> we need to implement the lifecycle of liveupdate agent correctectly,
> where owner of FD must survive through entering into reboot() with
> /dev/liveupdate still open.

Yes, by this point we should ensure refcnt == 1. IIUC you plan to
implement the lifecycle change in the next revision, so this can be
added there as well I suppose.

[...]

-- 
Regards,
Pratyush Yadav