Re: [Qemu-devel] qemu-nbd vs 'simple' trace backend vs iotest 147

[Paolo Bonzini]

On 12/07/2018 18:30, Stefan Hajnoczi wrote:
> On Wed, Jul 11, 2018 at 03:33:21PM +0200, Cornelia Huck wrote:
>> The other qemu-nbds (the inet and the unix socket ones from the first
>> run, the second inet one from the second run) have a single thread with
>> the same backtrace I posted above.
> 
> We just discussed this on IRC, but for the record:
> 
> qemu-nbd --fork will fork the process after the simpletrace write-out
> thread has been spawned.  The child process lacks this thread (due to
> how fork(2) handles multithreading).  Either qemu-nbd needs to
> initialize tracing later (but that means we cannot trace early init) or
> simpletrace needs a way to respawn the write-out thread.

You can use pthread_atfork for this.

Paolo

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