[PATCH 08/21] Unionfs: Introduce branch-id code

[Josef 'Jeff' Sipek]

From: Erez Zadok <ezk@xxxxxxxxxxxxx>

Each branch gets a unique ID, which helps during branch additions,
deletions, and changes, to locate where branches were moved to, and perform
proper reference-counting.  This is useful even if the same directory was
added more than once to union.

Signed-off-by: Erez Zadok <ezk@xxxxxxxxxxxxx>
Signed-off-by: Josef 'Jeff' Sipek <jsipek@xxxxxxxxxxxxx>
---
 fs/unionfs/commonfops.c |   62 +++++++++++++++++++++++++++++++++++++++++++++-
 fs/unionfs/fanout.h     |   22 ++++++++++++++++-
 fs/unionfs/main.c       |    1 +
 fs/unionfs/union.h      |    4 ++-
 4 files changed, 85 insertions(+), 4 deletions(-)

diff --git a/fs/unionfs/commonfops.c b/fs/unionfs/commonfops.c
index aa7c75d..8d0f8d1 100644
--- a/fs/unionfs/commonfops.c
+++ b/fs/unionfs/commonfops.c
@@ -86,6 +86,31 @@ out:
 	return err;
 }
 
+/*
+ * Find new index of matching branch with an open file, since branches could
+ * have been added/deleted causing the one with open files to shift.
+ *
+ * @file: current file whose branches may have changed
+ * @bindex: index of branch within current file (could be old branch)
+ * @new_sb: the new superblock which may have new branch IDs
+ * Returns index of newly found branch (0 or greater), -1 otherwise.
+ */
+static int find_new_branch_index(struct file *file, int bindex,
+				 struct super_block *new_sb)
+{
+	int old_branch_id = UNIONFS_F(file)->saved_branch_ids[bindex];
+	int i;
+
+	for (i = 0; i < sbmax(new_sb); i++)
+		if (old_branch_id == branch_id(new_sb, i))
+			return i;
+	/*
+	 * XXX: maybe we should BUG_ON if not found new branch index?
+	 * (really that should never happen).
+	 */
+	return -1;
+}
+
 /* put all references held by upper struct file and free lower file pointer
  * array
  */
@@ -93,6 +118,7 @@ static void cleanup_file(struct file *file)
 {
 	int bindex, bstart, bend;
 	struct file **lf;
+	struct super_block *sb = file->f_dentry->d_sb;
 
 	lf = UNIONFS_F(file)->lower_files;
 	bstart = fbstart(file);
@@ -100,13 +126,29 @@ static void cleanup_file(struct file *file)
 
 	for (bindex = bstart; bindex <= bend; bindex++) {
 		if (unionfs_lower_file_idx(file, bindex)) {
-			branchput(file->f_dentry->d_sb, bindex);
+			int i;	/* holds (possibly) updated branch index */
+			i = find_new_branch_index(file, bindex, sb);
+			if (i < 0)
+				printk(KERN_ERR "unionfs: no supberlock for file %p\n",
+				       file);
+			else {
+				unionfs_read_lock(sb);
+				branchput(sb, i);
+				unionfs_read_unlock(sb);
+				/* XXX: is it correct to use sb->s_root here? */
+				unionfs_mntput(sb->s_root, i);
+				/* XXX: mntget b/c fput below will call mntput */
+				unionfs_mntget(sb->s_root, bindex);
+			}
 			fput(unionfs_lower_file_idx(file, bindex));
 		}
 	}
 
 	UNIONFS_F(file)->lower_files = NULL;
 	kfree(lf);
+	kfree(UNIONFS_F(file)->saved_branch_ids);
+	/* set to NULL because caller needs to know if to kfree on error */
+	UNIONFS_F(file)->saved_branch_ids = NULL;
 }
 
 /* open all lower files for a given file */
@@ -270,6 +312,12 @@ int unionfs_file_revalidate(struct file *file, int willwrite)
 			err = -ENOMEM;
 			goto out;
 		}
+		size = sizeof(int) * sbmax(sb);
+		UNIONFS_F(file)->saved_branch_ids = kzalloc(size, GFP_KERNEL);
+		if (!UNIONFS_F(file)->saved_branch_ids) {
+			err = -ENOMEM;
+			goto out;
+		}
 
 		if (S_ISDIR(dentry->d_inode->i_mode)) {
 			/* We need to open all the files. */
@@ -297,8 +345,10 @@ int unionfs_file_revalidate(struct file *file, int willwrite)
 	}
 
 out:
-	if (err)
+	if (err) {
 		kfree(UNIONFS_F(file)->lower_files);
+		kfree(UNIONFS_F(file)->saved_branch_ids);
+	}
 out_nofree:
 	unionfs_unlock_dentry(dentry);
 	unionfs_read_unlock(dentry->d_sb);
@@ -418,6 +468,12 @@ int unionfs_open(struct inode *inode, struct file *file)
 		err = -ENOMEM;
 		goto out;
 	}
+	size = sizeof(int) * sbmax(inode->i_sb);
+	UNIONFS_F(file)->saved_branch_ids = kzalloc(size, GFP_KERNEL);
+	if (!UNIONFS_F(file)->saved_branch_ids) {
+		err = -ENOMEM;
+		goto out;
+	}
 
 	dentry = file->f_dentry;
 	unionfs_lock_dentry(dentry);
@@ -456,6 +512,7 @@ int unionfs_open(struct inode *inode, struct file *file)
 out:
 	if (err) {
 		kfree(UNIONFS_F(file)->lower_files);
+		kfree(UNIONFS_F(file)->saved_branch_ids);
 		kfree(UNIONFS_F(file));
 	}
 out_nofree:
@@ -487,6 +544,7 @@ int unionfs_file_release(struct inode *inode, struct file *file)
 		}
 	}
 	kfree(fileinfo->lower_files);
+	kfree(fileinfo->saved_branch_ids);
 
 	if (fileinfo->rdstate) {
 		fileinfo->rdstate->access = jiffies;
diff --git a/fs/unionfs/fanout.h b/fs/unionfs/fanout.h
index e8c0fee..9e4a35f 100644
--- a/fs/unionfs/fanout.h
+++ b/fs/unionfs/fanout.h
@@ -32,12 +32,29 @@ static inline struct unionfs_inode_info *UNIONFS_I(const struct inode *inode)
 #define sbstart(sb) 0
 #define sbend(sb) (UNIONFS_SB(sb)->bend)
 #define sbmax(sb) (UNIONFS_SB(sb)->bend + 1)
+#define sbhbid(sb) (UNIONFS_SB(sb)->high_branch_id)
 
 /* File to private Data */
 #define UNIONFS_F(file) ((struct unionfs_file_info *)((file)->private_data))
 #define fbstart(file) (UNIONFS_F(file)->bstart)
 #define fbend(file) (UNIONFS_F(file)->bend)
 
+/* macros to manipulate branch IDs in stored in our superblock */
+static inline int branch_id(struct super_block *sb, int index)
+{
+	return UNIONFS_SB(sb)->data[index].branch_id;
+}
+
+static inline void set_branch_id(struct super_block *sb, int index, int val)
+{
+	UNIONFS_SB(sb)->data[index].branch_id = val;
+}
+
+static inline void new_branch_id(struct super_block *sb, int index)
+{
+	set_branch_id(sb, index, ++UNIONFS_SB(sb)->high_branch_id);
+}
+
 /* File to lower file. */
 static inline struct file *unionfs_lower_file(const struct file *f)
 {
@@ -52,11 +69,14 @@ static inline struct file *unionfs_lower_file_idx(const struct file *f, int inde
 static inline void unionfs_set_lower_file_idx(struct file *f, int index, struct file *val)
 {
 	UNIONFS_F(f)->lower_files[index] = val;
+	/* save branch ID (may be redundant?) */
+	UNIONFS_F(f)->saved_branch_ids[index] =
+		branch_id((f)->f_dentry->d_sb, index);
 }
 
 static inline void unionfs_set_lower_file(struct file *f, struct file *val)
 {
-	UNIONFS_F(f)->lower_files[fbstart(f)] = val;
+	unionfs_set_lower_file_idx((f), fbstart(f), (val));
 }
 
 /* Inode to lower inode. */
diff --git a/fs/unionfs/main.c b/fs/unionfs/main.c
index a37916d..ed264c7 100644
--- a/fs/unionfs/main.c
+++ b/fs/unionfs/main.c
@@ -515,6 +515,7 @@ static int unionfs_read_super(struct super_block *sb, void *raw_data,
 	UNIONFS_SB(sb)->bend = -1;
 	atomic_set(&UNIONFS_SB(sb)->generation, 1);
 	init_rwsem(&UNIONFS_SB(sb)->rwsem);
+	UNIONFS_SB(sb)->high_branch_id = -1; /* -1 == invalid branch ID */
 
 	hidden_root_info = unionfs_parse_options(sb, raw_data);
 	if (IS_ERR(hidden_root_info)) {
diff --git a/fs/unionfs/union.h b/fs/unionfs/union.h
index df9b8c0..7bd6306 100644
--- a/fs/unionfs/union.h
+++ b/fs/unionfs/union.h
@@ -80,6 +80,7 @@ struct unionfs_file_info {
 
 	struct unionfs_dir_state *rdstate;
 	struct file **lower_files;
+	int *saved_branch_ids; /* IDs of branches when file was opened */
 };
 
 /* unionfs inode data in memory */
@@ -123,6 +124,7 @@ struct unionfs_data {
 	struct super_block *sb;
 	atomic_t open_files;	/* number of open files on branch */
 	int branchperms;
+	int branch_id;		/* unique branch ID at re/mount time */
 };
 
 /* unionfs super-block data in memory */
@@ -131,7 +133,7 @@ struct unionfs_sb_info {
 
 	atomic_t generation;
 	struct rw_semaphore rwsem; /* protects access to data+id fields */
-
+	int high_branch_id;	/* last unique branch ID given */
 	struct unionfs_data *data;
 };
 
-- 
1.5.0.3.268.g3dda

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