lkml.org 
[lkml]   [2012]   [Apr]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH RFC v3] vfs: make fstatat retry once on ESTALE errors from getattr call
    On Mon, Apr 23, 2012 at 08:00:12AM -0400, Jeff Layton wrote:
    > On Sun, 22 Apr 2012 07:40:57 +0200
    > Miklos Szeredi <miklos@szeredi.hu> wrote:
    >
    > > On Fri, Apr 20, 2012 at 11:13 PM, Jeff Layton <jlayton@redhat.com> wrote:
    > > > On Fri, 20 Apr 2012 15:37:26 -0500
    > > > Malahal Naineni <malahal@us.ibm.com> wrote:
    > > >
    > > >> Steve Dickson [SteveD@redhat.com] wrote:
    > > >> > > 2) if we assume that it is fairly representative of one, how can we
    > > >> > > achieve retrying indefinitely with NFS, or at least some large finite
    > > >> > > amount?
    > > >> > The amount of looping would be peer speculation. If the problem can
    > > >> > not be handled by one simple retry I would say we simply pass the
    > > >> > error up to the app... Its an application issue...
    > > >>
    > > >> As someone said, ESTALE is an incorrect errno for a path based call.
    > > >> How about turning ESTALE into ENOENT after a retry or few retries?
    > > >>
    > > >
    > > > It's not really the same thing. One could envision an application
    > > > that's repeatedly renaming a new file on top of another one. The file
    > > > is never missing from the namespace of the server, but you could still
    > > > end up getting an ESTALE.
    > > >
    > > > That would break other atomicity guarantees in an even worse way, IMO...
    > >
    > > For directory operations ESTALE *is* equivalent to ENOENT if already
    > > retrying with LOOKUP_REVAL. Think about it. Atomic replacement by
    > > another directory with rename(2) is not an excuse here actually.
    > > Local filesystems too can end up with IS_DEAD directory after lookup
    > > in that case.
    > >
    >
    > Doesn't that violate POSIX? rename(2) is supposed to be atomic, and I
    > can't see where there's any exception for that for directories.

    Hm, but that only allows atomic replacement of the last component of a
    path.

    Suppose you're looking up a path, you've so far reached intermediate
    directory "D", and the next step of the lookup (of some entry in D)
    returns ESTALE. Then either:

    - D has since been unlinked, and ENOENT is obviously right.
    - D was unlinked and then replaced by something else, in which
    case there was still a moment when ENOENT was correct.
    - D was replaced atomically by a rename. But for the rename to
    work it must have been replacing an empty directory, so there
    was still a moment when ENOENT would have been correct.
    (Exception: if D was actually a regular file or some other
    non-directory object, then ENOTDIR would be the right error:
    but if you're able to get at least object type atomically with
    a lookup, then you should have noticed this already on lookup
    of D.)

    I think that's what Miklos meant?

    --b.


    \
     
     \ /
      Last update: 2012-04-23 15:03    [W:0.029 / U:122.596 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site