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Subject[PATCH 54/73] union-mount: Add generic_readdir_fallthru() helper [ver #2]
Date
From: Valerie Aurora <vaurora@redhat.com>

In readdir(), client file systems need to lookup the target of a
fallthru in a lower layer for three reasons: (1) fill in d_ino, (2)
fill in d_type, (2) make sure there is something to fall through to
(and if not, don't return this dentry). Create a generic helper
function.

Original-author: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/union.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/union.h | 10 ++++++++++
include/linux/fs.h | 15 +++++++++++++++
3 files changed, 78 insertions(+), 0 deletions(-)

diff --git a/fs/union.c b/fs/union.c
index 0c0490f..8efed50 100644
--- a/fs/union.c
+++ b/fs/union.c
@@ -386,3 +386,56 @@ out_fput:
mnt_drop_write(topmost_path->mnt);
return error;
}
+
+/* Relationship between i_mode and the DT_xxx types */
+static inline unsigned char dt_type(struct inode *inode)
+{
+ return (inode->i_mode >> 12) & 15;
+}
+
+/**
+ * generic_readdir_fallthru - Helper to lookup target of a fallthru
+ * @topmost_dentry: dentry for the topmost dentry of the dir being read
+ * @name: name of fallthru dirent
+ * @namelen: length of @name
+ * @ino: return inode number of target, if found
+ * @d_type: return directory type of target, if found
+ *
+ * In readdir(), client file systems need to lookup the target of a
+ * fallthru in a lower layer for three reasons: (1) fill in d_ino, (2)
+ * fill in d_type, (2) make sure there is something to fall through to
+ * (and if not, don't return this dentry). Upon detecting a fallthru
+ * dentry in readdir(), the client file system should call this function.
+ *
+ * Returns 0 on success and -ENOENT if no matching directory entry was
+ * found (which can happen when the topmost file system is unmounted
+ * and remounted over a different file system than). Any other errors
+ * are unexpected.
+ */
+int generic_readdir_fallthru(struct dentry *topmost_dentry, const char *name,
+ int namlen, ino_t *ino, unsigned char *d_type)
+{
+ struct path *parent;
+ struct dentry *dentry;
+ unsigned int i, layers = topmost_dentry->d_sb->s_union_count;
+
+ BUG_ON(!mutex_is_locked(&topmost_dentry->d_inode->i_mutex));
+
+ for (i = 0; i < layers; i++) {
+ parent = union_find_dir(topmost_dentry, i);
+ mutex_lock(&parent->dentry->d_inode->i_mutex);
+ dentry = lookup_one_len(name, parent->dentry, namlen);
+ mutex_unlock(&parent->dentry->d_inode->i_mutex);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+ if (dentry->d_inode) {
+ *ino = dentry->d_inode->i_ino;
+ *d_type = dt_type(dentry->d_inode);
+ dput(dentry);
+ return 0;
+ }
+ dput(dentry);
+ }
+ return -ENOENT;
+}
+EXPORT_SYMBOL(generic_readdir_fallthru);
diff --git a/fs/union.h b/fs/union.h
index a77bd5f..46944b9 100644
--- a/fs/union.h
+++ b/fs/union.h
@@ -71,6 +71,8 @@ extern int union_add_dir(struct path *, struct path *, unsigned int);
extern int union_create_topmost_dir(struct path *, struct qstr *, struct path *,
struct path *);
extern int union_copyup_dir(struct path *);
+extern int generic_readdir_fallthru(struct dentry *topmost_dentry, const char *name,
+ int namlen, ino_t *ino, unsigned char *d_type);

static inline
struct path *union_find_dir(struct dentry *dentry, unsigned int layer)
@@ -137,4 +139,12 @@ static inline int union_copyup_dir(struct path *topmost_path)
return 0;
}

+static inline
+int generic_readdir_fallthru(struct dentry *topmost_dentry, const char *name,
+ int namlen, ino_t *ino, unsigned char *d_type)
+{
+ BUG();
+ return 0;
+}
+
#endif /* CONFIG_UNION_MOUNT */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e130d00..46b35ea 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2569,6 +2569,21 @@ extern int generic_file_fsync(struct file *, loff_t, loff_t, int);

extern int generic_check_addressable(unsigned, u64);

+#ifdef CONFIG_UNION_MOUNT
+extern int generic_readdir_fallthru(struct dentry *topmost_dentry, const char *name,
+ int namlen, ino_t *ino, unsigned char *d_type);
+#else
+static inline int generic_readdir_fallthru(struct dentry *topmost_dentry, const char *name,
+ int namlen, ino_t *ino, unsigned char *d_type)
+{
+ /*
+ * Found a fallthru on a kernel without union support.
+ * There's nothing to fall through to, so return -ENOENT.
+ */
+ return -ENOENT;
+}
+#endif
+
#ifdef CONFIG_MIGRATION
extern int buffer_migrate_page(struct address_space *,
struct page *, struct page *,


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