Re: [PATCH v6 0/5] Add preadv & pwritev system calls.

Ulrich Drepper wrote:

If they are in the kernel there is no reason not to export them from
glibc.

Great.

But I have a general comment about all kinds of read syscalls.
If think they have been misdesigned from day one and if we are going to
add new ones we might want to fix them.

The problem is that they don't allow for zero-copy operations in enough
cases.  The kernel is not free to store the data wherever it wants even
if the userlevel code is fine with that.

[ ... more text snipped ... ]

I do see the point in adding a interface like this ...

   ssize_t readz (int fd, void *buf, size_t len, void **res)

... to help the kernel do zero-copy I/O.

I think system calls for vector I/O are *not* the right place for that
though.  Usually applications use vectored I/O because they *do* care
about the place the data is stored, because vectored I/O allows them to
avoid copying data within the application.

cheers,
  Gerd