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SubjectRe: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support
Tejun Heo <> writes:

> Implement FUSE direct mmap support. The server can redirect client
> mmap requests to any SHMLBA aligned offset in the custom address space
> attached to the fuse channel. The address space is managed by the
> server using mmap/munmap(2). The SHMLBA alignment requirement is
> necessary to avoid cache aliasing issues on archs with virtually
> indexed caches as FUSE direct mmaps are basically shared memory
> between clients and the server.
> The direct mmap address space is backed by pinned kernel pages which
> are allocated on the first fault either from a client or the server.
> If used carelessly, this can easily waste and drain memory.
> Currently, a server must have CAP_SYS_ADMIN to manage dmmap regions by
> mmapping and munmapping the channel fd.

Does that mean that for example in unionfs-fuse when a user wants to
mmap a file I can just mmap the actual underlying file from the real
filesystem and any read/write access would then shortcut fuse and go
directly to the real file?


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