Re: [PATCH] stream_to_pack: xread does not guarantee to read all requested bytes

From: Johannes Sixt <j6t@kdbg.org>
Date: Aug 20, 2013, 18:27 UTC
Message-ID: <5213B52F.7030205@kdbg.org>
In-Reply-To: <CALWbr2yaQaCte6+Y3GEa8Hxyhq6GPS64aTNzkGo8pdpcd9ZVUg@mail.gmail.com>

Am 20.08.2013 17:16, schrieb Antoine Pelisse:

> I was actually wondering when it's better to use xread() over
> read_in_full() ? Considering that we don't know if xread() will read
> the whole buffer or not, would it not be better to always use
> read_in_full() ?

Of course, you know whether the whole buffer was filled: xread() returns the number of bytes read. Same for xwrite().

> I guess there is a drawback to this, but I'm not
> exactly sure what it is.

The disadvantage of read_in_full() is that it can happen that it reads data from the stream successfully, but then reports an error. In this case, the data read is lost.

Analogously, when write_in_full() writes (some) data successfully, but ultimately fails, you don't know how much was written successfully.

-- Hannes