Dealing with the sendfile mess

[Andrew Bartlett]

On Thu, 2004-10-21 at 10:15, Jeremy Allison wrote:
> On Thu, Oct 21, 2004 at 08:51:31AM +1000, Andrew Bartlett wrote:
> > 
> > The issue, as Steve discovered, is that on failure, our sendfile code
> > will revert to a *normal* read request, despite having already sent the
> > SMB header.  This means the header is sent twice, and it all goes to
> > mush from here.
> 
> Is it a case of sendfile just failing ? I never got a good
> report of the exact problem.

That's why I decided to start discussion here, as I think it's possible
to prove this issue from source code.

Presume that for some reason sendfile fails - Steve claimed it was
possible for it to return ENOSYS in odd situations.  Currently, we
exit_server() for any other error, and send headers twice for ENOSYS
(see the goto in the write&X code). 

> > As we discussed on IRC, there seem to be two fixes we need.  We just
> > need to handle normal error cases better - file truncated under us etc,
> > and the lack of a functioning sendfile() at any given moment.
> 
> Actually we don't have to handle this case, tridge proved that
> returning zeros is ok here.

My point exactly.  We just need to actually do this (looking at the
code, I think we exit_server() instead).

> The returning the header twice is just a bug and we should
> be able to fix that. The issue is how do we know the header
> has been returned ? If the sendfile failed - where in the
> returning stream did it fail ? 

See, the problem is that linux sendfile does not take a headers
argument, and sys_sendfile() in this case does the write, then asks
sendfile to send the data.

I'm proposing that the 'sendfile failed' code should be specific to the
sys_sendfile() implementation.  This will allow us to tell where it
failed, and chose the appropriate recovery.  (Which may still be
exit_server()).

Andrew Bartlett

-- 
Andrew Bartlett                                 abartlet at samba.org
Authentication Developer, Samba Team            http://samba.org
Student Network Administrator, Hawker College   abartlet at hawkerc.net
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