[illumos-Developer] [REVIEW] 260 some drivers erroneously discount a major of 0

[Gordon Ross]

On Fri, Oct 1, 2010 at 11:04 AM, Garrett D'Amore <garrett at damore.org> wrote:
> dump(7d) uses major 0 on my system.  I think we just have recognize that
> 0 is a valid major number.

Yes, zero is valid.  Unfortunately, the real world contains lots of code that
uses default initialization (to zero) so uninitialized major or dev_t values
are unfortunately likely to hit that slot in the devopsp vector.  I suggest
that it's a small price to pay to reserve slot zero to avoid accidents with
such (admittedly incorrect) drivers and such.

Gordon


>        - Garrett
>
> On Thu, 2010-09-30 at 21:52 -0400, Gordon Ross wrote:
>> Looks fine to me.
>>
>> I wonder if there is any reasonable way on an existing system to move
>> whatever driver might be using major zero to some other major number?
>> If so, you could skip the 2nd and 3rd file changes.
>>
>> On Tue, Sep 28, 2010 at 1:36 AM, Richard Lowe <richlowe at richlowe.net> wrote:
>> >
>> > I'd like review of:
>> >   260 some drivers erroneously discount a major of 0
>> >
>> > webrev: http://richlowe.net/webrevs/il-maj0/
>> >
>> > This bug is the same as:
>> >  6975280 t_kopen() fails if transport major device = 0
>> >
>> > As noted in the bug (#260), the change to add_drv prevents major 0 being
>> > given to drivers (it means, for new images, major numbers will start
>> > from 1), this is due to the impossibility of auditing every driver for
>> > assumptions regarding (dev_t)0 (especially those from 3rd parties), and
>> > the apparently fairly widespread assumption that such a dev_t is
>> > invalid.  The only code I found with such assumptions is t_kopen, and in
>> > addition sv, as mentioned in the bug.
>> >
>> > I've tested this via add_drv -b, with an empty name_to_major, to verify
>> > that the first driver it adds gets major 1, with a partially complete
>> > name_to_major, to make sure that the 'gap' at 0 is not filled, and by
>> > wiring tcp(7D) to major 0 to test the circumstances mentioned in 6975280
>> > (both before and after).
>> >
>> > I have not yet found a good way to test 'sv', though the change seems
>> > obvious I'm entirely willing to (and would prefer to) revert it, unless
>> > a volunteer can come up with a reasonable way to test it.  You would
>> > need the device underlying sv to have both a major and minor number of
>> > 0.
>> >
>> > Garrett has already looked at this, and given some general sense of
>> > assent.
>> >
>> > If you plan to look at this but require more time, please say so,
>> > so that I know to wait for you.
>> >
>> > -- Rich
>> >
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