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SubjectRe: [PATCH 10/41] whiteout: Add vfs_whiteout() and whiteout inode operation
On Sun, Nov 29, 2009 at 10:04:16PM -0500, Erez Zadok wrote:
> In message <1256152779-10054-11-git-send-email-vaurora@redhat.com>, Valerie Aurora writes:
> > From: Jan Blunck <jblunck@suse.de>
> >
> > Simply white-out a given directory entry. This functionality is usually used
> > in the sense of unlink. Therefore the given dentry can still be in-use and
> > contains an in-use inode. The filesystems inode operation has to do what
> > unlink or rmdir would in that case. Since the dentry still might be in-use
> > we have to provide a fresh unhashed dentry that is used as the whiteout
> > dentry instead. The given dentry is dropped and the whiteout dentry is
> > rehashed instead.
> >
> > Signed-off-by: Jan Blunck <jblunck@suse.de>
> > Signed-off-by: David Woodhouse <dwmw2@infradead.org>
> > Signed-off-by: Valerie Aurora <vaurora@redhat.com>
> > ---
> > fs/dcache.c | 4 +-
> > fs/namei.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/dcache.h | 6 +++
> > include/linux/fs.h | 3 +
> > 4 files changed, 116 insertions(+), 1 deletions(-)
> >
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index 3415e9e..0fcae4b 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -1076,8 +1076,10 @@ struct dentry *d_alloc_name(struct dentry *parent, const char *name)
> > /* the caller must hold dcache_lock */
> > static void __d_instantiate(struct dentry *dentry, struct inode *inode)
> > {
> > - if (inode)
> > + if (inode) {
> > + dentry->d_flags &= ~DCACHE_WHITEOUT;
> > list_add(&dentry->d_alias, &inode->i_dentry);
> > + }
> > dentry->d_inode = inode;
> > fsnotify_d_instantiate(dentry, inode);
> > }
> > diff --git a/fs/namei.c b/fs/namei.c
> > index 46cf1cb..d2fc8c9 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -2169,6 +2169,110 @@ SYSCALL_DEFINE2(mkdir, const char __user *, pathname, int, mode)
> > return sys_mkdirat(AT_FDCWD, pathname, mode);
> > }
> >
> > +
> > +/* Checks on the victim for whiteout */
> > +static inline int may_whiteout(struct inode *dir, struct dentry *victim,
> > + int isdir)
>
> Why not make 'isdir' a boolean?
>
> I'd prefer to see more documentation above this function: explain what each
> arg does, return value, etc.

Indeed! I added descriptions of the new whiteout and fallthru VFS ops
to Documentation/filesystems/vfs.txt, where it belongs.

> > +/**
> > + * vfs_whiteout: creates a white-out for the given directory entry
> > + * @dir: parent inode
> > + * @dentry: directory entry to white-out
>
> Nit: is it 'white-out' or 'whiteout'? Whatever you choose is fine, but
> please use consistent hypenation/spelling everywhere (code, comments, and
> documentation).

Done, thanks.

> > + *
> > + * Simply white-out a given directory entry. This functionality is usually used
> > + * in the sense of unlink. Therefore the given dentry can still be in-use and
> > + * contains an in-use inode. The filesystem has to do what unlink or rmdir
>
> Nit: other than the line of comment just above, the other two instances of
> "in-use" in this comment (and the patch header) should be changed to "in
> use" (no hyphen).
>
> > + * would in that case. Since the dentry still might be in-use we have to
> > + * provide a fresh unhashed dentry that whiteout can fill the new inode into.
> > + * In that case the given dentry is dropped and the fresh dentry containing the
> > + * whiteout is rehashed instead. If the given dentry is unused, the whiteout
> > + * inode is instantiated into it instead.
> > + *
> > + * After this returns with success, don't make any assumptions about the inode.
>
> What kinds of assumptions one should not make? Perhaps it'd be better to
> document what you can/should assume, instead of what you shouldn't (or
> both?)
>
> > + * Just dput() it dentry.
>
> The last line is awkward: do you mean "its dentry"?

All rewritten to address the above comments.

Thanks,

-VAL


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