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From: Andy Shevchenko on 14 Jul 2010 11:10
2010/7/14 Michał Nazarewicz <m.nazarewicz(a)samsung.com>:
> On Wed, 14 Jul 2010 15:44:58 +0200, Andy Shevchenko
> <andy.shevchenko(a)gmail.com> wrote:
>>>> + *     fua=b[,b...]            Default false, booleans for ignore FUA
>>>> flag
>>>> + *                                     in SCSI WRITE(6,10,12) commands
>>>
>>> I wonder if it makes sense to make it per-LUN.  I 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.  This is a
>>> per-device property not really per-LUN.  As 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.  You 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.

>>>> +       if (sscanf(buf, "%d", &i) != 1)
>>>> +               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.  I'd use simpre_strol() myself.  Maybe even patched fsg_store_ro().
Agree, but better to do series of patches then, I guess.

>>>> +
>>>> +       if (curlun->fua)
>>>> +               fsg_lun_fsync_sub(curlun);
>
>>> Shouldn't that read something like:
>>>
>>> +       if (!curlun->fua && i)
>>> +               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.  That's why I proposed the &&.  With fua = 1 meaning
> ignore the flag my proposal would be:
>
> +       if (!i && curlun->fua)
> +               fsg_lun_fsync_sub(curlun);
Makes sense.

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


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With Best Regards,
Andy Shevchenko
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From: Michał Nazarewicz on 14 Jul 2010 13:20
> 2010/7/14 Michał Nazarewicz <m.nazarewicz(a)samsung.com>:
>> Ah, OK, I see why this is per LUN. You want to be able not to ignore
>> FUA if the backing storage is a removable media, right?

On Wed, 14 Jul 2010 17:05:07 +0200, Andy Shevchenko <andy.shevchenko(a)gmail.com> wrote:
> In instance, or vise versa.

I actually see the most sense in disabling FUA on devices with their
own power supply for logical units which backing file is not (on) a
removable device unless the removable device has some kind of lock
(like CD-ROM's door).

Either way, I now see the point of having this option per-LUN.

>>> Actually fua = 1 means ignorance of that flag.

>> ignore_fua would be better name then I think. This also stands for
>> module parameter.

Or even “nofua”. The other solution would be to change the meaning
to the opposite (1 meaning that FUA is not ignored).

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From: Felipe Balbi on 16 Jul 2010 04:00
Hi,

On Wed, Jul 14, 2010 at 04:55:33PM +0300, Roger Quadros wrote:
> file_storage driver does not deal with partitions. only mediums.

it deals with backing files, no matter if it's a medium, partition or a
file on a file system (using a loop-device).

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From: Roger Quadros on 16 Jul 2010 04:40
On 07/16/2010 10:54 AM, ext Felipe Balbi wrote:
> Hi,
>
> On Wed, Jul 14, 2010 at 04:55:33PM +0300, Roger Quadros wrote:
>> file_storage driver does not deal with partitions. only mediums.
>
> it deals with backing files, no matter if it's a medium, partition or a
> file on a file system (using a loop-device).
>
True, you are talking from the device side of the g_files_storage where it
accesses backing files, I was talking from the USB side, where g_file_storage
exposes LUNs or Mediums and not partitions.

br,
-roger
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From: Greg KH on 21 Jul 2010 15:20
On Thu, Jul 15, 2010 at 12:07:21PM +0300, Andy Shevchenko wrote:
> MS Windows mounts removable storage in "Removal optimized mode" by
> default. All the writes to the media are synchronous which is achieved
> by setting FUA (Force Unit Access) bit in SCSI WRITE(10,12) commands.
> This prevents I/O requests aggregation in block layer dramatically
> decreasing performance.
>
> This patch brings an option to accept or ignore mentioned bit
> a) via specifying module parameter "nofua", or
> b) through sysfs entry
> /sys/devices/platform/musb_hdrc/gadget/gadget-lun-N/nofua

Any new sysfs entry needs a matching documentation entry in the
Documentation/ABI/ directory.

Care to resend these two patches, with that documentation change added
as well?

thanks,

greg k-h
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