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    SubjectRe: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support
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    On Thu, 11 Feb 2010, Tejun Heo wrote:
    > > If there's a pattern there, we might make the sharing/non-sharing
    > > automated, and greatly simplify the interface.
    >
    > Isn't the interface pretty simple as it is?

    On one hand it's simple, on the other it has pretty weird limitations,
    considering that server side mmap shouldn't be mandatory. But of
    course if server side mmap isn't used, then the SHMLBA limitation is
    not necessary anymore so the implementation could choose an arbitrary
    "offset".

    My biggest gripe with the kernel API is that we shouldn't be calling
    that thing in fuse_mmap_out an offset at all, because it's not and
    it's confusing (like making you set vma->vm_pgoff to that value, which
    is bogus). Adding a separate "page_id" or whatever would make me
    happy.

    And if the server wants to mmap /dev/fuse then it can do that and send
    the result in "dev_offset", to make it clear that it's a different
    offset from the one the client used on the mmap. And it can even use
    that value as page_id, if it wants to or it can use a different
    page_id.

    Does that sound reasonable?

    > If we want to make it
    > easier for API users by imposing limits, I think the correct layer to
    > do that would be at the library level.

    Hmm, might do that. High level library users definitely shouldn't be
    having to mess around with SHMLBA.

    Thanks,
    Miklos


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