From f86fab116246a25dcf77f6a22881ccb87e44cc28 Mon Sep 17 00:00:00 2001
From: Zach Brown <zab@versity.com>
Date: Mon, 14 Nov 2016 14:52:28 -0800
Subject: [PATCH] Add an inode data_version field

The data_version field is changed every time the contents of the file
could have changed.

Signed-off-by: Zach Brown <zab@versity.com>
Reviewed-by: Mark Fasheh <mfasheh@versity.com>
---
 kmod/src/filerw.c |  5 +++++
 kmod/src/format.h |  5 +++++
 kmod/src/inode.c  | 31 ++++++++++++++++++++++++++++++-
 kmod/src/inode.h  |  5 +++++
 4 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/kmod/src/filerw.c b/kmod/src/filerw.c
index 841b5a01..daa975df 100644
--- a/kmod/src/filerw.c
+++ b/kmod/src/filerw.c
@@ -615,6 +615,11 @@ static int scoutfs_write_end(struct file *file, struct address_space *mapping,
 		     scoutfs_ino(inode), PGA(page), (u64)pos, len, copied);
 
 	ret = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
+	if (ret > 0) {
+		scoutfs_inode_inc_data_version(inode);
+		/* XXX kind of a big hammer, inode life cycle needs work */
+		scoutfs_update_inode_item(inode);
+	}
 	scoutfs_release_trans(sb);
 	return ret;
 }
diff --git a/kmod/src/format.h b/kmod/src/format.h
index 2b2b31b0..528b2e5d 100644
--- a/kmod/src/format.h
+++ b/kmod/src/format.h
@@ -200,6 +200,10 @@ struct scoutfs_timespec {
 } __packed;
 
 /*
+ * @data_version: incremented every time the contents of a file could
+ * have changed.  It is exposed via an ioctl and is then provided as an
+ * argument to data functions to protect racing modification.
+ *
  * XXX
  *	- otime?
  *	- compat flags?
@@ -211,6 +215,7 @@ struct scoutfs_inode {
 	__le64 size;
 	__le64 blocks;
 	__le64 link_counter;
+	__le64 data_version;
 	__le32 nlink;
 	__le32 uid;
 	__le32 gid;
diff --git a/kmod/src/inode.c b/kmod/src/inode.c
index 81a18a85..aabb0910 100644
--- a/kmod/src/inode.c
+++ b/kmod/src/inode.c
@@ -120,9 +120,10 @@ static void load_inode(struct inode *inode, struct scoutfs_inode *cinode)
 	inode->i_mtime.tv_nsec = le32_to_cpu(cinode->mtime.nsec);
 	inode->i_ctime.tv_sec = le64_to_cpu(cinode->ctime.sec);
 	inode->i_ctime.tv_nsec = le32_to_cpu(cinode->ctime.nsec);
-	
+
 	ci->salt = le32_to_cpu(cinode->salt);
 	atomic64_set(&ci->link_counter, le64_to_cpu(cinode->link_counter));
+	ci->data_version = le64_to_cpu(cinode->data_version);
 }
 
 static int scoutfs_read_locked_inode(struct inode *inode)
@@ -148,6 +149,31 @@ static int scoutfs_read_locked_inode(struct inode *inode)
 	return ret;
 }
 
+void scoutfs_inode_inc_data_version(struct inode *inode)
+{
+	struct scoutfs_inode_info *si = SCOUTFS_I(inode);
+
+	preempt_disable();
+	write_seqcount_begin(&si->seqcount);
+	si->data_version++;
+	write_seqcount_end(&si->seqcount);
+	preempt_enable();
+}
+
+u64 scoutfs_inode_get_data_version(struct inode *inode)
+{
+	struct scoutfs_inode_info *si = SCOUTFS_I(inode);
+	unsigned int seq;
+	u64 vers;
+
+	do {
+		seq = read_seqcount_begin(&si->seqcount);
+		vers = si->data_version;
+	} while (read_seqcount_retry(&si->seqcount, seq));
+
+	return vers;
+}
+
 static int scoutfs_iget_test(struct inode *inode, void *arg)
 {
 	struct scoutfs_inode_info *ci = SCOUTFS_I(inode);
@@ -210,6 +236,7 @@ static void store_inode(struct scoutfs_inode *cinode, struct inode *inode)
 
 	cinode->salt = cpu_to_le32(ci->salt);
 	cinode->link_counter = cpu_to_le64(atomic64_read(&ci->link_counter));
+	cinode->data_version = cpu_to_le64(ci->data_version);
 }
 
 /*
@@ -366,6 +393,8 @@ struct inode *scoutfs_new_inode(struct super_block *sb, struct inode *dir,
 
 	ci = SCOUTFS_I(inode);
 	ci->ino = ino;
+	seqcount_init(&ci->seqcount);
+	ci->data_version = 0;
 	get_random_bytes(&ci->salt, sizeof(ci->salt));
 	atomic64_set(&ci->link_counter, 0);
 
diff --git a/kmod/src/inode.h b/kmod/src/inode.h
index 52ad52a6..1becde1d 100644
--- a/kmod/src/inode.h
+++ b/kmod/src/inode.h
@@ -5,6 +5,9 @@ struct scoutfs_inode_info {
 	u64 ino;
 	u32 salt;
 
+	seqcount_t seqcount;
+	u64 data_version;
+
 	atomic64_t link_counter;
 	struct rw_semaphore xattr_rwsem;
 
@@ -33,6 +36,8 @@ void scoutfs_dirty_inode(struct inode *inode, int flags);
 void scoutfs_update_inode_item(struct inode *inode);
 struct inode *scoutfs_new_inode(struct super_block *sb, struct inode *dir,
 				umode_t mode, dev_t rdev);
+void scoutfs_inode_inc_data_version(struct inode *inode);
+u64 scoutfs_inode_get_data_version(struct inode *inode);
 
 int scoutfs_scan_orphans(struct super_block *sb);