Re: zero-copy read() interface

[Folkert van Heusden <folkert@vanheusden.com>]

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> > What about a zero-copy read-interface?
> > An ioctl (or something) which enables the kernel to do dma directly to
> > the userspace. Of course this should be limited to the root-user or a
> > user with special capabilities (rights) since if a drive screws up, data
> > from a different sector (or so) might end up in the proces' memory. Of
> > course copying a sector from kernel- to userspace can be done pretty
> > fast but i.m.h.o. all possible speedimprovements should be made unless
> > unclean.
> Just use mmap().  Unlike your proposal, it cooperates with the page
> cache.

Doesn't that one also use copying? I've also heard that using mmap is
expensive due to pagefaulting. I've found, for example, that copying a
1.3GB file using read/write instead of mmap & memcpy is seconds faster.


Folkert van Heusden

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