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    SubjectRe: [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.


    > 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.


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