Dealing with the sendfile mess

[Andrew Bartlett]

On Thu, 2004-10-21 at 08:51, Andrew Bartlett wrote:
> Samba 3.0.7 has been rather a mess, due to the change in the default of
> 'use sendfile'.  The failure cases for this call are not well handled,
> causing mayhem particularly with Linux clients.  
> 
> Steve French caught me on IRC and described it, but hasn't mentioned it
> here, so I figured I needed to raise it.  It is important, because of
> the potential for data corruption.
> 
> 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.
> 
> 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.

BTW, I can't see the code that is meant to exist for the truncation case
- I thought we were meant to block-fill it with zero up to the old
length, but I don't see the zero writes...

> We can do this by having sys_sendfile() handle all the cases, and
> avoiding the two codepaths that caused this bug to occur in the first
> place.  If sys_sendfile() were implemented for systems without a real
> sendfile() API, then we would always take the same codepath.  Likewise,
> if the sendfile() call fails, we should just continue with read() and
> write(), but within the sys_sendfile() call.
> 
> If this is all just a bit too much, then we need to get 'use sendfile'
> turned back off, until we have time to deal with this properly.
> 
> 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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