Re: [PATCHv2] usb: gadget: storage: optional SCSI WRITE FUA bit

[Andy Shevchenko]

2010/7/14 MichaÅ Nazarewicz <m.nazarewicz@xxxxxxxxxxx>:
> On Wed, 14 Jul 2010 15:44:58 +0200, Andy Shevchenko
> <andy.shevchenko@xxxxxxxxx> wrote:
>>>> + * Â Â fua=b[,b...] Â Â Â Â Â ÂDefault false, booleans for ignore FUA
>>>> flag
>>>> + * Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â in SCSI WRITE(6,10,12) commands
>>>
>>> I wonder if it makes sense to make it per-LUN. ÂI would imagine
>>> that it's great to ignore FUA if the device has its own power supply
>>> in which case after disconnect the data won't be lost. ÂThis is a
>>> per-device property not really per-LUN. ÂAs such I'd make this option
>>> global for the gadget.
>
>> Make sense only for removable media with one partition.
>> Otherwise. why we have sync option per partition f.e., not per device?
>
> Ah, OK, I see why this is per LUN. ÂYou want to be able not to ignore
> FUA if the backing storage is a removable media, right?
In instance, or vise versa.
So, the user could decide if he wants to avoid this flag for one LUN
or for another.

>>>> + Â Â Â if (sscanf(buf, "%d", &i) != 1)
>>>> + Â Â Â Â Â Â Â return -EINVAL;
>>> Why not simple_strtol() directly?
>> I did it in the same way like fsg_store_ro() does.
>> I have no objections to back to previous solution.
> OK. ÂI'd use simpre_strol() myself. ÂMaybe even patched fsg_store_ro().
Agree, but better to do series of patches then, I guess.

>>>> +
>>>> + Â Â Â if (curlun->fua)
>>>> + Â Â Â Â Â Â Â fsg_lun_fsync_sub(curlun);
>
>>> Shouldn't that read something like:
>>>
>>> + Â Â Â if (!curlun->fua && i)
>>> + Â Â Â Â Â Â Â fsg_lun_fsync_sub(curlun);
>>>
>>> ie. there is no sense in syncing if FUA was active (in which case all
>>> writes were synced already, right?) or if the new value is false (since
>>> then user does not won't syncing).
>
>> The idea is to sync data before switching from async mode.
>
> But there can be a case of switching from async to async when syncing
> is not necessary. ÂThat's why I proposed the &&. ÂWith fua = 1 meaning
> ignore the flag my proposal would be:
>
> + Â Â Â if (!i && curlun->fua)
> + Â Â Â Â Â Â Â fsg_lun_fsync_sub(curlun);
Makes sense.

>> Actually fua = 1 means ignorance of that flag.
> ignore_fua would be better name then I think. ÂThis also stands for
> module parameter.
I already thought about. Rather I agree with you.


-- 
With Best Regards,
Andy Shevchenko
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