Unix FD Passing

Thiago Macieira thiago at kde.org
Fri Apr 24 16:13:58 PDT 2009

Em Sexta-feira 24 Abril 2009, às 18:55:16, Lennart Poettering escreveu:
> This also includes simple negotiation for unix fd passing: the auth
> protocol is extended a bit. Two new commands have been introduced. If
> a clients can do and wants to do fd passing it will send
> NEGOTIATE-UNIX-FD after the authentication was sucessful, before
> sending BEGIN. The server then responds with ERROR if it cannot or
> doesn't want to do fd passing. Otherwise it will respond with
> AGREE-UNIX-FD and both sides enable their fd passing code.

Brilliant solution! Why didn't we think of that before?

> There are some other changes in the repo too: a few commits regarding
> FD_CLOEXEC: newer linux kernels have support for SOCK_CLOEXEC which
> allows sockets to be created with O_CLOEXEC set right-away. This
> closes a race condition where some other thread might fork/exec while
> dbus allocated an fd and hasn't yet set FD_CLOEXEC. Given how
> fundamental D-Bus is it is certainly good idea to fix this race.

Thanks, I was going to do that myself (I'm doing the same for Qt and I sent a 
patch to glib), but you beat me to the punch here.

On that:
db2a3283 and 96a70e0a
	- older kernels will return EINVAL for the "| SOCK_CLOEXEC" case
	  you need to try again without
808ceff7 and df664ffe
	- same thing: you may be on a glibc that has pipe2/accept4, but the kernel
	  doesn't, so the call will return ENOSYS and you should try again

I didn't find any dup or dup2 calls that needed fixing (all dup2 are after 

Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Software
      PGP/GPG: 0x6EF45358; fingerprint:
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