[BRLTTY] how to use brltty on mac

[John Covici]

There is no patch in the Documents directory of the brltty I checked
out from git.  The git has your latest commit, so is it somewhere
else?

On Sun, 03 Sep 2017 13:49:18 -0400,
Dave Mielke wrote:
> 
> [quoted lines by rmgls on 2017/09/03 at 18:03 +0200]
> 
> >I changed the permissions at compile time of the screen executable that I 
> >sent. Screen.c
> 
> That isn't necessary. If you start with pure screen source and apply our patch, 
> it will work. If it doesn't then something else is wrong.
> 
> Tehre's another issue, too. Users have an implicit trust when getting source 
> from official sources. I wouldn't dare run any executable that's been modified 
> by anyone who doesn't have a well established reputation. They're either 
> running this stuff as themselves or as root, and they simply, and rightly, 
> don't want to take any chances.
> 
> >    shmid = shmget( key, size, IPC_CREAT | S_IRWXU | 660);
> 
> This modified line actually is a case in point. S_IRWXU is a constant that has 
> the octal value 0700, i.e. user-only permissions. That's correct. Adding more 
> bits makes the user's screen viewable by others, which is exactly what he 
> doesn't want.
> 
> Now let's look at the 660 that's being ored to the correct value. While 660 may 
> be correct chmod syntax, that's only because chmod is expecting an octal value. 
> In C, 660 is being interpreted as a decimal number. 660 decimal works out to 
> being 1224 octal. That's clearly a bad value for the permissions of a shared 
> memory segment. Even if 660 were interpreted as octal, it'd be adding group 
> permissions and that's not what a user would want anyway.
> 
> So please go back to pure screen source with just our patch applied. I'm going 
> to guess regarding what the problem may be.
> 
> Screen needs to be started first (at least for the first time) to ensure that 
> the shared memory segment is created before brltty tries to find it. Then 
> brltty must be started, and it must be started by the very same user who 
> started screen. This is nencessary for at least three reasons. First, that's 
> the only way for user-only permissions to allow access. Second, it's the only 
> way for both programs to be implicitly looking for the same shared memory 
> segment. Third, shared memory segments are private by default which means that, 
> without a bit of extra work, another user wouldn't be able to find it.
> 
> -- 
> Dave Mielke           | 2213 Fox Crescent | http://Mielke.cc/
> Phone: 1-613-726-0014 | Ottawa, Ontario   | http://Mielke.cc/bible/
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-- 
Your life is like a penny.  You're going to lose it.  The question is:
How do
you spend it?

         John Covici
         covici at ccs.covici.com