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    SubjectRe: [PATCH 31/41] fallthru: Support for fallthru entries in union mount lookup
    In message <1256152779-10054-32-git-send-email-vaurora@redhat.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@suse.de>
    > Signed-off-by: Valerie Aurora <vaurora@redhat.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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