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SubjectRe: [PATCH 3/6] fms: Add TOC/PMA/ATIP DVD-ROM capabilities
On Sun, Jun 27, 2021 at 09:45:07PM +0300, i.kononenko wrote:
>
>
> On 27.06.2021 17:29, Alan Stern wrote:
> > Is any of this really needed? What usage scenarios require
> > f_mass_storage to emulate a DVD-ROM that couldn't use f_tcm instead?
>
> I can't see any impediments to supplement the already existing
> implementation of MMC-(2/3) specification of multimedia devices to
> represent the DVD/BD features. If the kernel presents the CD-ROM SCSI
> commands, why the mass_storage:usb-gadget-function still doesn't include
> that for DVD/BD?
>
> Many modern embedded systems (e.g., BMC, OpenBMC) implements their
> required features, e.g., Virtual Media Device, which is based on the
> usb:gadget:mass-storage.
> The purpose of that features is extensive, and their use the mass-storage
> not only as a cdrom-device.
>
> The required features of such systems might expect image back-end files
> that size is significant than 2.1Gb, but such medium is not the CD-ROM
> device. USB-gadget consumers can incorrectly interpret such device by
> loading the wrong driver. I believe that should be the DVD-medium device,
> at least.

You should include this information in the patch description, so that
people will understand why you wrote the patch.

> Additionally, please note the current patch also fixes the incorrect
> implementation of retrieving TOC/PMA/ATIP data, which is required for the
> CD-ROM. One system might correct works with retrieving first with the
> last session together, but for some systems, e.g., OS ESXi, OS Windows,
> should retrieving first and last border sessions in separate SCSI-request.

What's wrong with the existing implementation? Are you talking about
the do_read_toc function? The driver only supports one session in any
case.

In general, fixes to existing code and additions of new code should go
in separate patches.

Alan Stern

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