DragonFly BSD
DragonFly kernel List (threaded) for 2003-07
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Re: just curious

From: Peter da Silva <peter-dragonfly@xxxxxxxxxxx>
Date: Mon, 21 Jul 2003 12:13:05 -0500

Matthew Dillon wrote:
    Yes.  Compare it against the Mach 'I'm going to map the data into your
    address space' model.  There will be some cases where having the kernel
    map the address space is more efficient (saving two system calls),
    but most of the time there is no need or reason to map the data and in
    those cases passing a descriptor is far more efficient.

Indeed. Most of the layering cases that Terry Lambert was presenting as
potential problems can be avoided by passing these kinds of handles around. Plus, they could easily be exposed over the network via NFS or sockets to non-dragonfly operating systems and applications. For a webserver that would allow for a heck of an optimization: just open a file readonly and then attach the client's socket to it... with smart enough hardware you could practically DMA straight from the SCSI card to the ethernet card. Or you could move most of NFS to user mode and still get kernel NFS performance...

copyfile(int sfd, int dfd, off_t soffset, off_t doffset, off_t bytes)

I assume this operation would end up being implemented by changing the state of VM buffers, yes?

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