Re: [PATCHv2] usb: gadget: storage: optional SCSI WRITE FUA bit
From: Roger Quadros
Date: Wed Jul 14 2010 - 09:55:55 EST
On 07/14/2010 04:44 PM, ext Andy Shevchenko wrote:
2010/7/14 MichaÅ 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?
by partition do you mean medium? They are different terms.
A storage medium may have 1 or more logical partitions. It is left upto the
Host/user to decide how he wants to partition the medium.
file_storage driver does not deal with partitions. only mediums.
regards,
-roger
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