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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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