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    SubjectRe: Important for fs devs: rcu-walk merged upstream
    On Fri, Jan 14, 2011 at 3:18 AM, Miklos Szeredi <> wrote:
    > On Thu, 13 Jan 2011, Miklos Szeredi wrote:
    >> On Sat, 8 Jan 2011, Nick Piggin wrote:
    >> > The vfs-scale branch is now upstream. If you haven't
    >> > looked yet, your filesystem is likely to have been
    >> > touched, so check it out.
    >> >
    >> > Also look at Documentation/filesystems/porting and
    >> > path-lookup.txt.
    >> >
    >> > The dcache_lock stuff should have been all done for you
    >> > (for in-tree filesystems, I can help out of tree fses with
    >> > conversions there if you ping me offline).
    >> >
    >> > The rcu-walk stuff can be more tricky for your filesystem
    >> > to take advantage of.
    >> >
    >> > If you supply a .d_revalidate, .permission, or .check_acl,
    >> > then path walking is going to be slow and unscalable for
    >> > you.
    >> >
    >> > Out of tree filesystems: you _have_ to at least add a line
    >> > of code to the above functions in order to specify that
    >> > you don't want to participate in rcu-walk.
    >> >
    >> > Otherwise, you don't have to care about rcu-walk if you
    >> > have a legacy or special filesystem like configfs then I'd
    >> > advise against anything fancy. But if you have a
    >> > userbase and you expect them to actually do any path
    >> > lookups into your filesystem, please take a look.
    >> One other thing: I know ECHILD is safe since no sane filesystem will
    >> return it in its permission or revalidate callbacks, and even if it
    >> does that's just a loss of optimization.
    > And it's not entirely safe either.  A fuse filesystem returning ECHILD
    > would make nameidata_dentry_drop_rcu() to BUG.  So some sort of errno
    > filter is necessary in the fuse kernel module.

    Surely you'd need some filtering anyway? I don't think any function
    involving path lookup could sanely return -ECHILD.

    That said, it probably is a good idea to have a new errno.
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      Last update: 2011-01-14 02:25    [W:0.051 / U:66.560 seconds]
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