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    Subject[PATCH 31/41] fallthru: Support for fallthru entries in union mount lookup
    Date
    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).
    + */
    +
    /**
    * __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))
    + 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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