[PATCH -V2 1/3] vfs: Add name to file handle conversion support

["Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>]

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
---
 fs/open.c          |   80 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |    7 ++++
 2 files changed, 87 insertions(+), 0 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index e17f544..7012cf9 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -30,6 +30,7 @@
 #include <linux/falloc.h>
 #include <linux/fs_struct.h>
 #include <linux/ima.h>
+#include <linux/exportfs.h>
 
 #include "internal.h"
 
@@ -1206,3 +1207,82 @@ int nonseekable_open(struct inode *inode, struct file *filp)
 }
 
 EXPORT_SYMBOL(nonseekable_open);
+
+/* limit the handle size to some value */
+#define MAX_HANDLE_SZ 4096
+static int do_sys_name_to_handle(const char __user *name,
+				struct file_handle *fh)
+{
+	int retval;
+	int handle_size;
+	struct path path;
+	struct inode *inode;
+	void *handle = NULL;
+
+	if (fh->handle_size > MAX_HANDLE_SZ)
+		return -EINVAL;
+
+	retval = user_lpath(name, &path);
+	if (retval)
+		return retval;
+
+	inode = path.dentry->d_inode;
+	/*
+	 * name to handle conversion only done for regular files
+	 * directories and symbolic links
+	 */
+	if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode) &&
+		!S_ISLNK(inode->i_mode)) {
+		retval =  -EINVAL;
+		goto err_out;
+	}
+	handle = kmalloc(fh->handle_size, GFP_KERNEL);
+	if (!handle) {
+		retval = -ENOMEM;
+		goto err_out;
+	}
+
+	handle_size = fh->handle_size;
+	/* we ask for a non connected handle */
+	retval = exportfs_encode_fh(path.dentry, (struct fid *)handle,
+				&handle_size,  0);
+	/* convert handle size to bytes */
+	handle_size *= sizeof(u32);
+	fh->handle_type = retval;
+	if (handle_size <= fh->handle_size) {
+		if (copy_to_user(fh->f_handle, handle,
+					handle_size))
+			retval = -EFAULT;
+		else
+			retval = 0;
+	} else
+		retval = -EOVERFLOW;
+	fh->handle_size = handle_size;
+	kfree(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;
+}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 10b8ded..e618cac 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -948,6 +948,13 @@ 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);
-- 
1.7.0.2.273.gc2413

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