[sane-devel] Avision bug (was: Re: Suicidal Child Process - SANE)

m. allan noah kitno455 at gmail.com
Sun Jan 11 13:46:47 UTC 2009

On Sun, Jan 11, 2009 at 8:10 AM, Mattias Ellert
<mattias.ellert at fysast.uu.se> wrote:
> 22 dec 2008 kl. 02.31 skrev m. allan noah:
>>> On Tue, Dec 9, 2008 at 10:48 AM, Mattias Ellert
>>> <mattias.ellert at fysast.uu.se> wrote:
>>>> mån 2008-12-08 klockan 09:46 -0500 skrev m. allan noah:
>>>>> After some private mails with Ian, it seems this is a bug in
>>>>> sane-avision:
>>>>> during sane_cancel(), the backend calls: sanei_thread_kill
>>>>> (s->reader_pid), but s->reader_pid is 0, which signals the entire
>>>>> group. There is a test to try and avoid this, but it relies on prior
>>>>> code to have set s->reader_pid = -1, which has not happened in the
>>>>> case of no paper.
>>>>> I just expanded the test to require a positive value, since the pid
>>>>> should never be negative anyway? My fix has just been commited to CVS
>>>>> (backend version 289 nice round number for Ford and Studebaker fans).
>>>>> Ian and Rene- please test.
>>>>> allan
>>>> This breaks the MacOS X port. The PID number (being a pointer) can be
>>>> arbitrary large, and when cast to an integer it can easily overflow to a
>>>> negative value. The code was fixed for this problem by removing all
>>>> places where the code was checking for a PID > 0. For the avision
>>>> backend this was done here:
>>>> https://alioth.debian.org/plugins/scmcvs/cvsweb.php/sane-backends/backend/avision.c.diff?r1=1.38;r2=1.39;cvsroot=sane
>>>> Your commit:
>>>> https://alioth.debian.org/plugins/scmcvs/cvsweb.php/sane-backends/backend/avision.c.diff?r1=1.43;r2=1.44;cvsroot=sane
>>>> reintroduces the problem fixed by the earlier commit. Please revert it
>>>> and fix the new problem in a way that doesn't break the MacOS X port.
>> Ok, so what is the correct fix? If OSX is using pthread, is it enough
>> to make SANE_Pid pthread_t?
>> allan
> The SANE_Pid is properly declared as:
> #ifdef USE_PTHREAD
> typedef long SANE_Pid;
> #else
> typedef int SANE_Pid;
> #endif
> This gives the correct size for both fork and pthread on both 32 and 64 bit.
> Changing it to pid_t and pthread_t instead of int and long would mean an
> interface change (and we get into the change soname or not discussion again)
> - you would also loose the abstraction achieved by using an opaque type in
> the SANE API rather than the implementation specific types.

Correct me if i am wrong, but we are talking about sanei here, not the
sane API. None of this is in the API.

> Also since the SANE API states that a SANE_Pid value of -1 indicates an
> error, the SANE_Pid must be a signed type.

Where does it state this? I dont see SANE_Pid anywere in the API.

 Changing it to pthread_t (which
> essentially is a pointer - hence an unsigned type) will break the API badly.
> Any value for a unsigned type will always be different from -1 (a good
> compiler will optimise the check away).
> The only thing that must remembered is that negative values for SANE_Pid are
> valid (except for -1). You can not check for a valid SANE_Pid with (pid >
> 0).

Pointers could wrap to -1 as well. This fix is not sufficient. I think
we can correct this the right way in sanei.

"The truth is an offense, but not a sin"

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