[RFC] patch to add support for leases to cifs

["Steve French" <smfrench@gmail.com>]

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fcntl(F_SETLEASE) currently is not exported by cifs (nor by local file
systems) so cifs grants leases based on how other local processes have
opened the file not by whether the file is cacheable (oplocked).  This
adds the check to make sure that the file is cacheable on the client
before checking whether we can grant the lease locally
(generic_setlease).



-- 
Thanks,

Steve

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diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index c6aad77..aaa6f37 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -618,6 +618,26 @@ static loff_t cifs_llseek(struct file *file, loff_t offset, int origin)
 	return generic_file_llseek_unlocked(file, offset, origin);
 }
 
+#ifdef CONFIG_CIFS_EXPERIMENTAL
+static int cifs_setlease(struct file *file, long arg, struct file_lock **lease)
+{
+	/* note that this is called by vfs setlease with the BKL held
+	   although I doubt that BKL is needed here in cifs */
+
+	if (!(S_ISREG(inode->i_mode))
+		return -EINVAL;
+
+	/* check if file is oplocked */
+	if (((arg == F_RDLCK) &&
+		(CIFS_I(file->f_path.dentry->d_inode)->clientCanCacheRead)) ||
+	    ((arg == F_WRLCK) &&
+		(CIFS_I(file->f_path.dentry->d_inode)->clientCanCacheAll)))
+		return generic_setlease(file, arg, lease);
+	else
+		return -EAGAIN;
+}
+#endif
+
 struct file_system_type cifs_fs_type = {
 	.owner = THIS_MODULE,
 	.name = "cifs",
@@ -696,6 +716,7 @@ const struct file_operations cifs_file_ops = {
 
 #ifdef CONFIG_CIFS_EXPERIMENTAL
 	.dir_notify = cifs_dir_notify,
+	.setlease = cifs_setlease,
 #endif /* CONFIG_CIFS_EXPERIMENTAL */
 };
 
@@ -716,6 +737,7 @@ const struct file_operations cifs_file_direct_ops = {
 	.llseek = cifs_llseek,
 #ifdef CONFIG_CIFS_EXPERIMENTAL
 	.dir_notify = cifs_dir_notify,
+	.setlease = cifs_setlease,
 #endif /* CONFIG_CIFS_EXPERIMENTAL */
 };
 const struct file_operations cifs_file_nobrl_ops = {
@@ -736,6 +758,7 @@ const struct file_operations cifs_file_nobrl_ops = {
 
 #ifdef CONFIG_CIFS_EXPERIMENTAL
 	.dir_notify = cifs_dir_notify,
+	.setlease = cifs_setlease,
 #endif /* CONFIG_CIFS_EXPERIMENTAL */
 };
 
@@ -755,6 +778,7 @@ const struct file_operations cifs_file_direct_nobrl_ops = {
 	.llseek = cifs_llseek,
 #ifdef CONFIG_CIFS_EXPERIMENTAL
 	.dir_notify = cifs_dir_notify,
+	.setlease = cifs_setlease,
 #endif /* CONFIG_CIFS_EXPERIMENTAL */
 };
 
@@ -946,6 +970,12 @@ static int cifs_oplock_thread(void *dummyarg)
 				the call */
 			/* mutex_lock(&inode->i_mutex);*/
 			if (S_ISREG(inode->i_mode)) {
+#ifdef CONFIG_CIFS_EXPERIMENTAL
+				if (CIFS_I(inode)->clientCanCacheAll == 0)
+					break_lease(inode, FMODE_READ);
+				else if (CIFS_I(inode)->clientCanCacheRead == 0)
+					break_lease(inode, FMODE_WRITE);
+#endif
 				rc = filemap_fdatawrite(inode->i_mapping);
 				if (CIFS_I(inode)->clientCanCacheRead == 0) {
 					waitrc = filemap_fdatawait(