On Sunday, 22 August 1999 at 17:31:44 -0700, Matthew Dillon wrote:
>
>> Questions:
>>
>> 1. Do we have some form of mandatory locking? If so, what is it?
>
> No we don't, unless you count the ad-hoc lockout in the master/slave pty
> interface :-).
>
>> 2. Would it make sense to implement System V's fcntl semantics?
>> They're rather tacky: you set the setgid bit and reset the group
>> exec bit of the file permissions.
>
> Ugh. Yuch. No, nothing to do with permission bits, not for something
> this convoluted!
I don't like it either, but for compatibility reasons it would make
sense. That's why I suggested a sysctl knob.
>> 3. Alternatively (or additionally), would it make sense to have an
>> additional fcntl function which performs mandatory locking?
>>
>> I think that it's probably a good idea to implement (3), and also to
>> do (2), possibly subject to a sysctl knob.
>
> Well, #3 can't be mandatory if you have to make a fcntl call!
Somehow you need to get a lock.
> You mean have one program make a fcntl call that causes other
> programs to return an error or block if they try to open that
> file while the first program holds an open descriptor?
Correct. I suppose it's worth discussing what the default should be.
Should they get EAGAIN or block? Obviously you'd want a way of
specifying which, but there would have to be a default for
non-lock-aware programs. I think I'd go for blocking; it's less error
prone.
Greg
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