On Sun, Jun 27, 2021 at 09:45:07PM +0300, i.kononenko wrote:
On 27.06.2021 17:29, Alan Stern wrote:
quoted
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