Re: [Qemu-devel] [RFC][PATCH]Add timestamp to error message

[Paolo Bonzini]

Il 04/04/2013 16:54, Laszlo Ersek ha scritto:
> Side note: strictly in theory, this would result in two vfprintf()
> calls. The message log would remain "record oriented", but (again, in
> theory) another thread *might* get interleaved and mess up our format
> with a parallel call to error_report() (or more deeply, to fprintf()).
> 
> Importantly I'm not talking about "corrupting data"; stdio streams are
> automatically locked by the fprintf() family. The thing (theoretically,
> possibly) corrupted would be our record-oriented message format, by
> interleaved printfs.
> 
> (a) I'm not sure if this is possible at all in qemu.

It would be one more thing that is protected by the big QEMU lock.

Regarding your other comment, please use gmtime_r, not gmtime.

Paolo

> (b) Anyway, there are two ways to fix it:
> 
> (b1) In error_report(), lock the stream across the two printfs with
> flockfile(). Probably overkill, and in case we're printing to the
> monitor, wasteful/useless. Or,

> (b2) Format the full message (including the timestamp) into a buffer
> (sprintf, vsprintf(), or their glib wrappers with automatic allocation,
> if any) and print it with a single error_printf("%s", buf).
> 
> Anyway I absolutely do not insist on this, so sorry for the noise.