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    SubjectRe: [PATCH 14/39] ovl: stack file ops
    On Wed, Jun 13, 2018 at 11:21:30AM +0200, Miklos Szeredi wrote:
    > On Tue, Jun 12, 2018 at 8:31 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
    > > On Tue, Jun 12, 2018 at 07:24:23PM +0100, Al Viro wrote:
    >
    > >> I hate it, but... consider path_open() objections withdrawn for now.
    >
    > Is that an ACK for the pull if I follow up with fixes for mmap botch, etc?

    Yes.

    > >> Uses of ->vm_file (and rules for those) are too convoluted to untangle
    > >> at the moment. I still would love to get that straightened out, but
    > >> it's not this cycle fodder, more's the pity...
    >
    > Looked at some other options... What coda mmap does looks very
    > dubious. It only sets f_mapping, not vm_file. That's going to get
    > into all sorts of trouble when underlying fs tries to look at
    > file_inode() or worse, ->private_data. Looks like that should be
    > converted to what overlayfs does, to have a remote chance of actually
    > not crashing on most filesystems. Does anybody actually use coda
    > still?

    Keep in mind that coda is using the local fs only as cache; IOW, its needs
    are much more limited than those of overlayfs - local r/w filesystem,
    disk-backed or tmpfs, used pretty much as a scratch space.

    > > PS: conversion of ->f_path.dentry is easy and that can probably go this
    > > cycle - it's a fairly trivial change, with no functional changes unless
    > > overlayfs is used with <filesystem>, fixing really bad shit if it ever
    > > gets used thus. I'm not asking to put that into overlayfs pull *and*
    > > it's independent from the "want to kill that fucking kludge" stuff.
    > > The latter is too hard for this cycle, unfortunately.
    >
    > So this is about adding a file_dentry_check() (or whatever we want to
    > call it) helper to be used by all filesystems when dereferecing
    > f_path.dentry, right?

    file_dentry(), and some of the users should be converted to file_inode().
    There's also a missing helper for debugfs uses - more or less a combination
    of file_dentry() and debugfs_file_get() (if not a conversion of
    debugfs_file_get() to taking struct file - almost all users are of that
    form, if not entirely all of them). I've some of that done in local
    branch...

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