Re: man page update (fcntl(2) new set/get write hints)

Jens Axboe
2017-08-25T20:55:22Z

On 08/25/2017 02:51 PM, Michael Kerrisk (man-pages) wrote:
>>>>> Do you mean here "file descriptor" or "file description (i.e., the
>>>>> open file handle)? Maybe you mean the former, but I want to confirm.
>>>>
>>>> I do mean file descriptor.
>>>
>>> So, what are the semantics if a file descriptor is duplicated using
>>> dup(2) or similar? If I understand correctly, then the write lifetime
>>> hint has no effect for the new file descriptor, right?
>>
>> If it's dup(2)'ed, then the new file descriptor will refer to the same
>> hints as the previous. See attached test file.
>
> But then isn't this exactly the point I asked about: are the hints
> private to a file descriptor or are they associated with the open file
> description (open file table entry, "struct file")? You said "I do
> mean file descriptor", but actually I understand what you just said
> now as "hints are associated with the open file description, which may
> be referred to by multiple duplicated file descriptors". Can you
> clarify?

You are right, I misunderstood your original question. They do follow
the file description. So the dup'ed one will return the same as the
original, even if the hints on the original fd get modified. That is the
expected behavior.

--
Jens Axboe