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Date: Mon, 30 Nov 2009 23:15:23 -0500
From: Erez Zadok <ezk@...sunysb.edu>
To: Valerie Aurora <vaurora@...hat.com>
Cc: Jan Blunck <jblunck@...e.de>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christoph Hellwig <hch@...radead.org>,
Andy Whitcroft <apw@...onical.com>,
Scott James Remnant <scott@...onical.com>,
Sandu Popa Marius <sandupopamarius@...il.com>,
Jan Rekorajski <baggins@...h.mimuw.edu.pl>,
"J. R. Okajima" <hooanon05@...oo.co.jp>,
Arnd Bergmann <arnd@...db.de>,
Vladimir Dronnikov <dronnikov@...il.com>,
Felix Fietkau <nbd@...nwrt.org>, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 31/41] fallthru: Support for fallthru entries in union mount lookup
In message <1256152779-10054-32-git-send-email-vaurora@...hat.com>, Valerie Aurora writes:
> A fallthru directory entry overrides the opaque flag for its parent
> directory (for this directory entry only). Before, we stopped
> building the union stack when we encountered an opaque directory; now
> we include directories below opaque directories in the union stack and
> check for opacity during lookup.
>
> Signed-off-by: Jan Blunck <jblunck@...e.de>
> Signed-off-by: Valerie Aurora <vaurora@...hat.com>
> ---
> fs/dcache.c | 7 +++----
> fs/namei.c | 59 +++++++++++++++++++++++++++++++++++++++++++++--------------
> 2 files changed, 48 insertions(+), 18 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index d80a3bb..ca8a661 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -1086,7 +1086,7 @@ struct dentry *d_alloc_name(struct dentry *parent, const char *name)
> static void __d_instantiate(struct dentry *dentry, struct inode *inode)
> {
> if (inode) {
> - dentry->d_flags &= ~DCACHE_WHITEOUT;
> + dentry->d_flags &= ~(DCACHE_WHITEOUT|DCACHE_FALLTHRU);
> list_add(&dentry->d_alias, &inode->i_dentry);
> }
> dentry->d_inode = inode;
> @@ -1638,9 +1638,8 @@ void d_delete(struct dentry * dentry)
>
> static void __d_rehash(struct dentry * entry, struct hlist_head *list)
> {
> -
> - entry->d_flags &= ~DCACHE_UNHASHED;
> - hlist_add_head_rcu(&entry->d_hash, list);
> + entry->d_flags &= ~DCACHE_UNHASHED;
> + hlist_add_head_rcu(&entry->d_hash, list);
> }
>
> static void _d_rehash(struct dentry * entry)
> diff --git a/fs/namei.c b/fs/namei.c
> index 8d95eb1..61e94aa 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -416,6 +416,28 @@ static struct dentry *cache_lookup(struct dentry *parent, struct qstr *name,
> return dentry;
> }
>
> +/*
> + * Theory of operation for opaque, whiteout, and fallthru:
> + *
> + * whiteout: Unconditionally stop lookup here - ENOENT
> + *
> + * opaque: Don't lookup in directories lower in the union stack
> + *
> + * fallthru: While looking up an entry, ignore the opaque flag for the
> + * current directory only.
> + *
> + * A union stack is a linked list of directory dentries which appear
> + * in the same place in the namespace. When constructing the union
> + * stack, we include directories below opaque directories so that we
> + * can properly handle fallthrus. All non-fallthru lookups have to
> + * check for the opaque flag on the parent directory and obey it.
> + *
> + * In general, the code pattern is to lookup the the topmost entry
> + * first (either the first visible non-negative dentry or a negative
> + * dentry in the topmost layer of the union), then build the union
> + * stack for the newly looked-up entry (if it is a directory).
> + */
Excellent comment; even better said and clearer that the UM design doc.
It's almost a pity such excellent description is buried in the middle of
namei.c.
> +
> /**
> * __cache_lookup_topmost - lookup the topmost (non-)negative dentry
> *
> @@ -445,6 +467,10 @@ static int __cache_lookup_topmost(struct nameidata *nd, struct qstr *name,
> if (!dentry || (dentry->d_inode || d_is_whiteout(dentry)))
> return !dentry;
>
> + /* Keep going through opaque directories if we found a fallthru */
> + if (IS_OPAQUE(nd->path.dentry->d_inode) && !d_is_fallthru(dentry))
> + return !dentry;
> +
> /* look for the first non-negative or whiteout dentry */
>
> while (follow_union_down(&nd->path.mnt, &nd->path.dentry)) {
> @@ -470,6 +496,10 @@ static int __cache_lookup_topmost(struct nameidata *nd, struct qstr *name,
> if (dentry->d_inode || d_is_whiteout(dentry))
> goto out_dput;
>
> + /* Stop the lookup on opaque parent and non-fallthru child */
> + if (IS_OPAQUE(nd->path.dentry->d_inode) && !d_is_fallthru(dentry))
There's a lot of repetition of this condition:
IS_OPAQUE(dentry->d_inode) && !d_is_fallthru(dentry)
in this patch. Perhaps this should be macro'ized?
#define CANT_GO_ON(d) (IS_OPAQUE((d)->d_inode) && !d_is_fallthru((d))) // :-)
> + goto out_dput;
> +
> dput(dentry);
> }
>
> @@ -528,9 +558,6 @@ static int __cache_lookup_build_union(struct nameidata *nd, struct qstr *name,
> path_put(&last);
> last.dentry = dentry;
> last.mnt = mntget(nd->path.mnt);
> -
> - if (IS_OPAQUE(last.dentry->d_inode))
> - break;
> }
>
> if (last.dentry != path->dentry)
> @@ -570,8 +597,7 @@ static int cache_lookup_union(struct nameidata *nd, struct qstr *name,
>
> /* only directories can be part of a union stack */
> if (!path->dentry->d_inode ||
> - !S_ISDIR(path->dentry->d_inode->i_mode) ||
> - IS_OPAQUE(path->dentry->d_inode))
> + !S_ISDIR(path->dentry->d_inode->i_mode))
> goto out;
>
> /* Build the union stack for this part */
> @@ -738,6 +764,9 @@ static int __real_lookup_topmost(struct nameidata *nd, struct qstr *name,
> if (path->dentry->d_inode || d_is_whiteout(path->dentry))
> return 0;
>
> + if (IS_OPAQUE(nd->path.dentry->d_inode) && !d_is_fallthru(path->dentry))
> + return 0;
> +
> while (follow_union_down(&nd->path.mnt, &nd->path.dentry)) {
> name->hash = full_name_hash(name->name, name->len);
> if (nd->path.dentry->d_op && nd->path.dentry->d_op->d_hash) {
> @@ -758,6 +787,9 @@ static int __real_lookup_topmost(struct nameidata *nd, struct qstr *name,
> goto out;
> }
>
> + if (IS_OPAQUE(nd->path.dentry->d_inode) && !d_is_fallthru(next.dentry))
> + goto out;
> +
> dput(next.dentry);
> }
> out:
> @@ -817,9 +849,6 @@ static int __real_lookup_build_union(struct nameidata *nd, struct qstr *name,
> path_put(&last);
> last.dentry = next.dentry;
> last.mnt = mntget(next.mnt);
> -
> - if (IS_OPAQUE(last.dentry->d_inode))
> - break;
> }
>
> if (last.dentry != path->dentry)
> @@ -841,8 +870,7 @@ static int real_lookup_union(struct nameidata *nd, struct qstr *name,
>
> /* only directories can be part of a union stack */
> if (!path->dentry->d_inode ||
> - !S_ISDIR(path->dentry->d_inode->i_mode) ||
> - IS_OPAQUE(path->dentry->d_inode))
> + !S_ISDIR(path->dentry->d_inode->i_mode))
> goto out;
>
> /* Build the union stack for this part */
> @@ -1128,7 +1156,7 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
> {
> int err;
>
> - if (IS_MNT_UNION(nd->path.mnt) && !IS_OPAQUE(nd->path.dentry->d_inode))
> + if (IS_MNT_UNION(nd->path.mnt))
> goto need_union_lookup;
>
> path->dentry = __d_lookup(nd->path.dentry, name);
> @@ -1679,6 +1707,9 @@ static int __hash_lookup_topmost(struct nameidata *nd, struct qstr *name,
> if (path->dentry->d_inode || d_is_whiteout(path->dentry))
> return 0;
>
> + if (IS_OPAQUE(nd->path.dentry->d_inode) && !d_is_fallthru(path->dentry))
> + return 0;
> +
> while (follow_union_down(&nd->path.mnt, &nd->path.dentry)) {
> name->hash = full_name_hash(name->name, name->len);
> if (nd->path.dentry->d_op && nd->path.dentry->d_op->d_hash) {
> @@ -1701,6 +1732,9 @@ static int __hash_lookup_topmost(struct nameidata *nd, struct qstr *name,
> goto out;
> }
>
> + if (IS_OPAQUE(nd->path.dentry->d_inode) && !d_is_fallthru(next.dentry))
> + goto out;
> +
> dput(next.dentry);
> }
> out:
> @@ -1755,9 +1789,6 @@ static int __hash_lookup_build_union(struct nameidata *nd, struct qstr *name,
> path_put(&last);
> last.dentry = next.dentry;
> last.mnt = mntget(next.mnt);
> -
> - if (IS_OPAQUE(last.dentry->d_inode))
> - break;
> }
>
> if (last.dentry != path->dentry)
> --
> 1.6.3.3
>
> --
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Erez.
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