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SubjectRe: [PATCH -V18 04/13] vfs: Allow handle based open on symlinks
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On Sat, 21 Aug 2010 15:12:15 +0530, "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> On Sat, 21 Aug 2010 18:30:24 +1000, Nick Piggin <npiggin@kernel.dk> wrote:
> > Thanks, I had both of the same concerns as Christoph with API
> > change and exposing symlink fds last time I looked at the patces,
> > actually.
> >
> > But they can probably be worked around or avoided. I think the more
> > important thing is whether it is worth supporting. This is
> > all restricted to root (or CAP_DAC_READ_SEARCH) only, right, and
> > what exact semantics they want. I would like to see more discussion
> > of what this enables and some results.
> >
> > For the case of avoiding expensive network revalidations in path name
> > lookup, do we even need to open symlinks? Could the security issues be
> > avoided by always having handle attached to an open fd?
> >
>
> For implementing a userspace file server that use handle for
> representing files (like NFS) we would require to have the ability to do
> different file system operations that can operate on symlink to work on
> handle too.
>

linkat change to take NULL path name is needed for regular files
also. The file server will get a request to create a link with handle
of oldpath and directory handle of new path and new name.

The changes would also help in the implementation of 9P server in Qemu
for implementing a fast virtualization passthrough file system (aka
VirtFS)

http://thread.gmane.org/gmane.comp.emulators.qemu/68992

-aneesh


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