Re: g_mass_storage module with large drives?

Re: g_mass_storage module with large drives?

[Felipe Balbi]

Hi Kim,

(please keep linux-usb@vger.kernel.org in Cc)

Kim Bak <kim.bak@gamereactor.dk> writes:

> Hi Felipe
>
> I'm not sure who or where to ask this question so i write directly to
> you.

we should include the mailing list ;-)

> I'm trying to get g_mass_storage to work with a large backing file or
> device, but it seems to be capped at 2Tb.
>
> This is probably limited by the 512 bytes block size.
>
> Is there any way to get the module to expose drives larger than 2Tb?

Should be possible, yes. Care to share any error messages you might get
in dmesg?

Also, which kernel version and USB Peripheral controller are you using?

> The module fails to work with Xbox Series X, i might be able to write
> up a real bug report on this, but I want to make sure that someone

Seems like you're dealing with two bugs:

1) Large backing stores don't work
2) Fails to work against Xbox Series X

> actually reads it first :)

Yeah, there's a ton of people reading the mailing list. If you want to
maximize your chances of getting a reply, it's always a great idead to
Cc the mailing list instead of sending an email only to the maintainer
;-)

Cheers

-- 
balbi

Re: g_mass_storage module with large drives?

[Alan Stern]

On Thu, Sep 02, 2021 at 02:02:14PM +0300, Felipe Balbi wrote:
> 
> Hi Kim,
> 
> (please keep linux-usb@vger.kernel.org in Cc)
> 
> Kim Bak <kim.bak@gamereactor.dk> writes:
> 
> > Hi Felipe
> >
> > I'm not sure who or where to ask this question so i write directly to
> > you.
> 
> we should include the mailing list ;-)
> 
> > I'm trying to get g_mass_storage to work with a large backing file or
> > device, but it seems to be capped at 2Tb.
> >
> > This is probably limited by the 512 bytes block size.

The driver doesn't support block sizes larger than 512 bytes for regular 
files.  But when a block device is used as the backing store, the driver 
uses the device's own logical block size, whatever that is.

Also, the driver doesn't support READ(16), WRITE(16), or related commands.  
Consequently it is limited to using only the first 2^32 blocks of the 
backing store.

> > Is there any way to get the module to expose drives larger than 2Tb?

Partition the drive into regions smaller than 2 TB and expose the different 
partitions as different logical units.  Or use a block device that has a 
larger block size.  Or modify the driver to add support for larger-capacity 
backing store.

Alan Stern