[Bug 1203559] Re: wodim doesn't find my DVD writer

[Ray Maslinski]

The change of device name should probably also be accompanied by an
update to the check_linux_26 function defined in the same scsi-linux-
sg.c file, which doesn't appear to deal with kernel major versions > 2:

BOOL check_linux_26() {
        int gen, tmp;
        struct utsname buf;
        return ( 0==uname( &buf ) && sscanf(buf.release, "%d.%d", &gen, &tmp)>1 
&& tmp>=6);
}

Note that the check is only looking for the minor version > 6, so the
behavior will revert to pre-2.6 device selection for kernel versions
3.0-3.5, 4.0-4.5, etc.

The pre-2.6 behavior uses /dev/sg* devices instead of /dev/scd* (or
/dev/sr* with the previously attached patch), probably due to lack of
support required in earlier driver versions.  While this will probably
work most of the time, I think there may be a potential for contention
with other applications using the device, as there doesn't appear to be
a locking mechanism across the /dev/sg* and /dev/sr* devices.  This
could allow (for example) an audio player using a /dev/sr* device to
interfere with wodim if it's using /dev/sg* for access.  Using the same
device driver for all access to the cd device should allow for
appropriate locking to prevent concurrent access.  There's a warning in
the code to this effect, though it seems to be disabled:

                                case(SG):
                                        {
                                                if(check_linux_26())
                                                        continue; 
#if 0
                                                /*
                                                 * Don't touch it on 2.6 until w
e have a proper locking scheme
                                                 */
                                                        if(nopen<=0)
                                                                fprintf(stderr, 
"Warning, using /dev/sg* for SG_IO operation. This method is considered harmful.
\n");
                                                        else if(found_scd)
                                                                continue;
#endif
                                                pattern="/dev/sg%d";
                                                first=0;
                                                last=255;
                                                break;
                                        }

There are a few other places referencing check_linux_26 beyond device
selection, presumably these would also behave more correctly with newer
kernels with a revised version check.

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https://bugs.launchpad.net/bugs/1203559

Title:
  wodim doesn't find my DVD writer

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