2010/7/14 Michał Nazarewicz <m.nazarewicz@xxxxxxxxxxx>:
> On Wed, 14 Jul 2010 11:05:31 +0200, Andy Shevchenko
> <andy.shevchenko@xxxxxxxxx> 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.
>
>> diff --git a/drivers/usb/gadget/file_storage.c
>> b/drivers/usb/gadget/file_storage.c
>> index b49d86e..45f58d9 100644
>> --- a/drivers/usb/gadget/file_storage.c
>> +++ b/drivers/usb/gadget/file_storage.c
>> @@ -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?
>> @@ -743,6 +752,24 @@ static ssize_t fsg_store_ro(struct device *dev,
>> struct device_attribute *attr,
>> return rc;
>> }
>> +static ssize_t fsg_store_fua(struct device *dev, struct device_attribute
>> *attr,
>> + const char *buf, size_t count)
>> +{
>> + ssize_t rc = count;
>
> Not really needed here.
See below
>
>> + struct fsg_lun *curlun = fsg_lun_from_dev(dev);
>> + int i;
>> +
>> + 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.
>> +
>> + 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.
Actually fua = 1 means ignorance of that flag.
--
With Best Regards,
Andy Shevchenko
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