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SubjectRe: [RFC 20/26] union-mount: Simple union-mount readdir implementation
On Mon, Jul 30, 2007 at 06:13:43PM +0200, Jan Blunck wrote:
> --- a/include/linux/union.h
> +++ b/include/linux/union.h
> @@ -53,6 +53,7 @@ extern void __shrink_d_unions(struct den
> extern int attach_mnt_union(struct vfsmount *, struct vfsmount *,
> struct dentry *);
> extern void detach_mnt_union(struct vfsmount *);
> +extern int readdir_union(struct file *, void *, filldir_t);
>
> #else /* CONFIG_UNION_MOUNT */
>
> @@ -69,5 +70,29 @@ extern void detach_mnt_union(struct vfsm
> #define detach_mnt_union(x) do { } while (0)
>
> #endif /* CONFIG_UNION_MOUNT */
> +
> +static inline int do_readdir(struct file *file, void *buf, filldir_t filler)
> +{
> + struct inode *inode = file->f_path.dentry->d_inode;
> + int res;
> +
> +#ifdef CONFIG_UNION_MOUNT
> + if (IS_MNT_UNION(file->f_path.mnt))
> + res = readdir_union(file, buf, filler);
> + else
> +#endif
> + {
> + mutex_lock(&inode->i_mutex);
> + res = -ENOENT;
> + if (!IS_DEADDIR(inode)) {
> + res = file->f_op->readdir(file, buf, filler);
> + file_accessed(file);
> + }
> + mutex_unlock(&inode->i_mutex);
> + }
> +
> + return res;
> +}

Here you are doing readdir_union for all the directories under a union
mount point, which is an overhead (building the readdir cache). Here is
the fix:

From: Bharata B Rao <bharata@linux.vnet.ibm.com>

Within a union mount point, there can be directories which don't have a
union stack underneath them. And readdir() doesn't have to maintain a cache
of dirents for such directories. But the current patch maintains the cache
for such directories. Fix this.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
---
fs/union.c | 17 +++++++++++++++++
include/linux/union.h | 11 ++++++-----
2 files changed, 23 insertions(+), 5 deletions(-)
--- a/fs/union.c
+++ b/fs/union.c
@@ -366,6 +366,23 @@ int follow_union_mount(struct vfsmount *
}

/*
+ * is_dir_unioned - check if the directory represented by @mnt and @dentry
+ * has a union stack underneath.
+ *
+ * Returns true if a union stack exists at this directory level, else returns
+ * false.
+ */
+int is_dir_unioned(struct vfsmount *mnt, struct dentry *dentry)
+{
+ struct union_mount *um;
+
+ spin_lock(&union_lock);
+ um = union_lookup(dentry, mnt);
+ spin_unlock(&union_lock);
+ return um ? 1: 0;
+}
+
+/*
* This must be called when unhashing a dentry. This is called with dcache_lock
* and unhashes all unions this dentry is in.
*/
--- a/include/linux/union.h
+++ b/include/linux/union.h
@@ -54,6 +54,7 @@ extern int attach_mnt_union(struct vfsmo
struct dentry *);
extern void detach_mnt_union(struct vfsmount *);
extern int readdir_union(struct file *, void *, filldir_t);
+extern int is_dir_unioned(struct vfsmount *, struct dentry *);
extern int union_relookup_topmost(struct nameidata *, int);
extern struct dentry *union_create_topmost(struct nameidata *, struct qstr *,
struct path *);
@@ -82,13 +83,14 @@ extern int union_copyup(struct nameidata

static inline int do_readdir(struct file *file, void *buf, filldir_t filler)
{
- struct inode *inode = file->f_path.dentry->d_inode;
int res;
+ struct inode *inode = file->f_path.dentry->d_inode;

#ifdef CONFIG_UNION_MOUNT
- if (IS_MNT_UNION(file->f_path.mnt))
- res = readdir_union(file, buf, filler);
- else
+ if (IS_MNT_UNION(file->f_path.mnt)) {
+ if (is_dir_unioned(file->f_path.mnt, file->f_path.dentry))
+ res = readdir_union(file, buf, filler);
+ } else
#endif
{
mutex_lock(&inode->i_mutex);
@@ -99,7 +101,6 @@ static inline int do_readdir(struct file
}
mutex_unlock(&inode->i_mutex);
}
-
return res;
}

Regards,
Bharata.
-
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