[Libcdio-devel] Warning of potential regression

[Thomas Schmitt]

Hi,

i have to raise a warning about the commit
diff at
  
http://git.savannah.gnu.org/gitweb/?p=libcdio.git;a=commitdiff;h=4e8eff137e4912f13f6740c3abf52e44430bcff8

Something went wrong with patching.
(I will have to practice that.)

Now is defined
  SCSI_MMC_DATA_NONE
but it is not interpreted in
  run_mmc_cmd_linux()

So it gets now mapped to 
  CGC_DATA_WRITE

But all libcdio MMC commands on Linux
effectively used
  CGC_DATA_READ
up to this change.
So it is untested whether the commands of
direction NONE work on all Linuxes with
  CGC_DATA_WRITE

On the other hand, the other six OS drivers all
evaluate e_direction and this mapped
SCSI_MMC_DATA_WRITE to their WRITE symbol.
(How much tested ?)


Thus the correction of the bug might have impact
on two functions in libcdio if performed on
Linux:
  mmc_start_stop_media(const CdIo_t *p_cdio, bool b_eject, bool b_immediate,
                     uint8_t power_condition)
uses
  SCSI_MMC_DATA_WRITE
which now gets into effect on Linux.
It was already in effect on the other OSes.
CDIO_MMC_GPCMD_START_STOP = 1Bh START/STOP UNIT
is a command with direction NONE.

The same with
  mmc_eject_media( const CdIo_t *p_cdio )
which uses 1Eh PREVENT/ALLOW MEDIA REMOVAL.


It also affects all applications which use
SCSI_MMC_DATA_WRITE on Linux.
(But we cannot simply continue with mapping
WRITE to READ, can we ?)


------------------------------------------------

Proposal:

- Change the two questionable SCSI_MMC_DATA_WRITE
  to SCSI_MMC_DATA_NONE.
  The other six OS drivers will for now continue
  to map this to their WRITE symbol. (I checked.)

- In gnu_linux.c either
  - interpret SCSI_MMC_DATA_NONE as CGC_DATA_NONE
    as i proposed in my patch.
  - or default SCSI_MMC_DATA_NONE to CGC_DATA_READ
    so that the two changed functions are back on
    READ again.

This is because i am quite sure that CGC_DATA_NONE
is ok on all Linux >= 2.4. Up to now it was more or
less ok to use CGC_DATA_READ within libcdio.
(How did mmc_set_speed() and
 mmc_set_blocksize_private() perform up to now ?
 They did not get their WRITE into effect before
 the change. Did they work anyway ?)


Have a nice day :)

Thomas