Re: Libpcap reentrancy and PF_RING patch

["Paolo Abeni" <paolo.abeni () telecomitalia it>]

hello,

On Thu, 2008-01-03 at 01:29 +0100, Luca Deri wrote:
> > Here handle->buffer refers to a memory mapped kernel buffer, which  
> > holds
> > the USB Request Blocks and related meta-data. To make the patch work  
> > is
> > necessary to perform a memcpy from the kernel buffer to the user
> > provided one, but this solution will remove the performance gain of  
> > the
> > memory mapped access.
>
> perhaps a spinlock will be enough?

Well, It the question is to ensure reentrancy, the lock is necessary
only to protect the break_loop field, since the data access is thread
safe 'as-is': the required locking/synchronization is provided by the
kernel via the ioctl call used to request the available URBs. 

Anyway, to implement your proposed API, the received URB must exposed to
the user into the provided buffer, so a copy is necessary. 

Please note that a similar problem will arise also if the patch to
enable memory mapped access to ethernet capture (currently pending) will
be accepted/merged.

ciao,

Paolo
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