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SubjectRe: [PATCHv2] usb: gadget: storage: optional SCSI WRITE FUA bit
On Wed, 14 Jul 2010 15:44:58 +0200, Andy Shevchenko <> wrote:
>>> @@ -93,6 +93,8 @@
>>> * removable Default false, boolean for removable media
>>> * luns=N Default N = number of filenames, number of
>>> * LUNs to support
>>> + * 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?

>>> + ssize_t rc = count;

>> Not really needed here.

> See below

This still stands. The “rc” is not needed.

>>> + 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().

>>> +
>>> + 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);

> Actually fua = 1 means ignorance of that flag.

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

Best regards, _ _
| Humble Liege of Serenely Enlightened Majesty of o' \,=./ `o
| Computer Science, Michał "mina86" Nazarewicz (o o)
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