Dealing with the sendfile mess
jpeach at sgi.com
Wed Oct 20 23:38:23 GMT 2004
On Thu, Oct 21, 2004 at 08:51:31AM +1000, 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.
Yep, I came across this adding while sendfile support to IRIX. My
(pretty obvious) solution was to detect the presence of a working
sendfile before trying to use it in anger. If it's not there, always
return ENOSYS without sending headers.
> 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.
So this would be the zero-filling behaviour Jeremy talked about at one
> 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.
This sounds like a useful refactorisation of the read reply paths.
James Peach | jpeach at sgi.com | SGI Australian Software Group
I don't speak for SGI.
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