Re: [patch] pipe: add support for shrinking and growing pipes

[Jens Axboe <jens.axboe@oracle.com>]

> The "at least" idea makes sense. So, I'd change my recommendation to:
> 
> Pass the buffer size in and out in bytes (for consistency with other
> APIs). Round the input (F_SETPIPE_SZ) value up as required by the
> implementation. For the output (F_GETPIPE_SZ) value do one of the
> following:
> a) Return the value given on input.
> b) Return the rounded up value actually used by the kernel.
> 
> I suspect (b) might be more useful: if an application cares enough
> about pipe size to want to change it, then at least some such
> applications might care to know exactly the size that the kernel used.
> (And: I can't see any downside to (b).)

b definitely, since it's the real size (plus then we don't have to track
the passed in size).

> One other comment about the interface. We have
> 
>                 if (!capable(CAP_SYS_ADMIN) && arg > pipe_max_pages)
>                         return -EINVAL;
> 
> The usual error on a capability denied is EPERM. Please change.

Right, that looks like a thinko.

I'll submit a patch changing it to bytes and the agreed API and fix this
-Eerror. Thanks for your comments and suggestions!

-- 
Jens Axboe