On Fri, Apr 05, 2013 at 12:56:09PM -0700, Greg Kroah-Hartman wrote:
> Which methods do you mean here?
file->f_op->some_method()
> The vfs core would call start_using(), or would filesystems / drivers
> need to do this?
The former; we have relatively few places that call file_operations
members directly and we'd turn each of those into
if (likely(start_using(file)) {
res = file->f_op->foo(....);
stop_using(file);
} else {
res = error_value_appropriate_for_foo;
}
> > 4) nasty semantics issue - mmap() vs. revoke (of any sort, including
> > remove_proc_entry(), etc.). Suppose a revokable file had been mmapped;
> > now it's going away. What should we do to its VMAs? Right now sysfs
> > and procfs get away with that, but only because there's only one thing
> > that has ->mmap() there - /proc/bus/pci and sysfs equivalents. I've
> > no idea how does pci_mmap_page_range() interact with PCI hotplug (and
> > I'm not at all sure that whatever it does isn't racy wrt device removal),
>
> The page range should just start returning 0xff all over the place, the
> BIOS should have kept the mapping around, as it can't really assign it
> anywhere else, so all _should_ be fine here.
Umm... 0xff or SIGSEGV?
> I think that's a reasonable constraint, although tearing down the VMAs
> might be possible if we just invalidate the file handle "forcefully"
> (i.e. manually tear them down and then further accesses should through a
> SIGSEV fail, or am I missing something more basic here?)
The question is how to do that in a reasonably clean way; we would've done
as part of ->kick(), I suppose, or right next to it.
> > 6) how do we get from revoke(2) to call of revoke_it() on the right object?
> > Note that revoke(2) is done by pathname; we might want an ...at() variant,
> > but all we'll have to play with will be inode, not an opened file.
>
> Can we make revoke(2) require a valid file handle? Is there a POSIX
> spec for revoke(2) that we have to follow here, or given that we haven't
> had one yet, are we free to define whatever we want without people
> getting that upset?
BSD one takes a pathname and so do all derived ones...
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