[RFC PATCH 1/3] vfs: Add name to file handle conversion support

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 fs/open.c          |   64 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |    7 +++++
 2 files changed, 71 insertions(+), 0 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 040cef7..f5a8420 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -31,6 +31,7 @@
 #include <linux/falloc.h>
 #include <linux/fs_struct.h>
 #include <linux/ima.h>
+#include <linux/exportfs.h>
 
 #include "internal.h"
 
@@ -1079,6 +1080,69 @@ SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, int, mode)
 	return ret;
 }
 
+static int do_sys_name_to_handle(const char __user *name,
+				struct file_handle *handle)
+{
+	int retval;
+	struct path path;
+	struct inode *inode;
+	void *f_handle = NULL;
+	int handle_size = handle->handle_size;
+
+	retval = user_lpath(name, &path);
+	if (retval)
+		return retval;
+
+	inode = path.dentry->d_inode;
+
+	f_handle = kmalloc(handle_size, GFP_KERNEL);
+	if (!f_handle) {
+		retval = -ENOMEM;
+		goto err_out;
+	}
+
+	/* we ask for a non connected handle */
+	retval = exportfs_encode_fh(path.dentry, (struct fid *)f_handle,
+				&handle_size,  0);
+	handle->handle_type = retval;
+	if (handle_size < handle->handle_size) {
+		if (copy_to_user(handle->f_handle, f_handle,
+					handle_size*sizeof(u32)))
+			retval = -EFAULT;
+		retval = 0;
+	} else
+		retval = -EAGAIN;
+	handle->handle_size = handle_size;
+	kfree(f_handle);
+
+err_out:
+	path_put(&path);
+	return retval;
+}
+
+SYSCALL_DEFINE2(name_to_handle, const char __user *, name,
+		struct file_handle __user *, handle)
+{
+	long ret;
+	struct file_handle f_handle;
+	if (copy_from_user(&f_handle, handle, sizeof(struct file_handle))) {
+		ret = -EFAULT;
+		goto err_out;
+	}
+	ret = do_sys_name_to_handle(name, &f_handle);
+	if (copy_to_user(&handle->handle_type,
+			&f_handle.handle_type, sizeof(f_handle.handle_type)) ||
+		copy_to_user(&handle->handle_size,
+			&f_handle.handle_size, sizeof(f_handle.handle_size))) {
+		ret = -EFAULT;
+	}
+err_out:
+	/* avoid REGPARM breakage on x86: */
+	asmlinkage_protect(2, ret, name, handle);
+	return ret;
+}
+
+
 SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
 		int, mode)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b1bcb27..5bef1e9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -945,6 +945,13 @@ struct file {
 	unsigned long f_mnt_write_state;
 #endif
 };
+
+struct file_handle {
+	int handle_size;
+	int handle_type;
+	void *f_handle;
+};
+
 extern spinlock_t files_lock;
 #define file_list_lock() spin_lock(&files_lock);
 #define file_list_unlock() spin_unlock(&files_lock);
-- 
1.7.0.31.g1df487