[PATCH RFC 01/11] vfs: pull btrfs clone API to vfs layer

[Peng Tao <tao.peng@primarydata.com>]

Now that a few file systems are adding clone functionality, namingly
btrfs, NFS (later in the series) and XFS
(ttp://oss.sgi.com/archives/xfs/2015-06/msg00407.html), it makes sense
to pull the ioctl to common code.

Add vfs_file_clone_range() helper and .clone_range file operation interface
to allow underlying filesystems to clone between regular files.

The change in do_vfs_ioctl() is defered to next patch where btrfs
.clone_range is added, just so that we don't break btrfs CLONE ioctl
with this patch.

Cc: linux-btrfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Peng Tao <tao.peng@primarydata.com>
---
 fs/ioctl.c              | 24 ++++++++++++++++++++++++
 fs/read_write.c         | 45 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h      |  4 ++++
 include/uapi/linux/fs.h |  9 +++++++++
 4 files changed, 82 insertions(+)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 5d01d26..726c5d7 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -215,6 +215,30 @@ static int ioctl_fiemap(struct file *filp, unsigned long arg)
 	return error;
 }
 
+static long ioctl_file_clone(struct file *dst_file, unsigned long srcfd,
+			     u64 off, u64 olen, u64 destoff)
+{
+	struct fd src_file = fdget(srcfd);
+	int ret;
+
+	if (!src_file.file)
+		return -EBADF;
+	ret = vfs_file_clone_range(src_file.file, dst_file, off, olen, destoff);
+
+	fdput(src_file);
+	return ret;
+}
+
+static long ioctl_file_clone_range(struct file *file, void __user *argp)
+{
+	struct file_clone_range args;
+
+	if (copy_from_user(&args, argp, sizeof(args)))
+		return -EFAULT;
+	return ioctl_file_clone(file, args.src_fd, args.src_offset,
+				args.src_length, args.dest_offset);
+}
+
 #ifdef CONFIG_BLOCK
 
 static inline sector_t logical_to_blk(struct inode *inode, loff_t offset)
diff --git a/fs/read_write.c b/fs/read_write.c
index 819ef3f..beaad2c 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -16,6 +16,7 @@
 #include <linux/pagemap.h>
 #include <linux/splice.h>
 #include <linux/compat.h>
+#include <linux/mount.h>
 #include "internal.h"
 
 #include <asm/uaccess.h>
@@ -1327,3 +1328,47 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
 	return do_sendfile(out_fd, in_fd, NULL, count, 0);
 }
 #endif
+
+int vfs_file_clone_range(struct file *src_file, struct file *dst_file,
+			 loff_t off, size_t len, loff_t dstoff)
+{
+	struct inode *src_ino;
+	struct inode *dst_ino;
+	ssize_t ret;
+
+	if (!(src_file->f_mode & FMODE_READ) ||
+	    !(dst_file->f_mode & FMODE_WRITE) ||
+	    (dst_file->f_flags & O_APPEND) ||
+	    !src_file->f_op || !src_file->f_op->clone_range)
+		return -EINVAL;
+
+	src_ino = file_inode(src_file);
+	dst_ino = file_inode(dst_file);
+
+        if (S_ISDIR(src_ino->i_mode) || S_ISDIR(dst_ino->i_mode))
+                return -EISDIR;
+
+	/* sanity check on offsets and length */
+	if (off + len < off || dstoff + len < dstoff ||
+	    off + len > i_size_read(src_ino))
+		return -EINVAL;
+
+	if (src_ino->i_sb != dst_ino->i_sb ||
+	    src_file->f_path.mnt != dst_file->f_path.mnt)
+		return -EXDEV;
+
+	ret = mnt_want_write_file(dst_file);
+	if (ret)
+		return ret;
+
+	ret = src_file->f_op->clone_range(src_file, dst_file, off, len, dstoff);
+	if (!ret) {
+		fsnotify_access(src_file);
+		fsnotify_modify(dst_file);
+	}
+
+	mnt_drop_write_file(dst_file);
+
+	return ret;
+}
+EXPORT_SYMBOL(vfs_file_clone_range);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cc008c3..612d7f4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1628,6 +1628,8 @@ struct file_operations {
 	long (*fallocate)(struct file *file, int mode, loff_t offset,
 			  loff_t len);
 	void (*show_fdinfo)(struct seq_file *m, struct file *f);
+	int (*clone_range)(struct file *src_file, struct file *dst_file,
+			   loff_t off, size_t len, loff_t dstoff);
 #ifndef CONFIG_MMU
 	unsigned (*mmap_capabilities)(struct file *);
 #endif
@@ -2678,6 +2680,8 @@ int __dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,
 int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
 #define dax_mkwrite(vma, vmf, gb, iod)		dax_fault(vma, vmf, gb, iod)
 #define __dax_mkwrite(vma, vmf, gb, iod)	__dax_fault(vma, vmf, gb, iod)
+int vfs_file_clone_range(struct file *src_file, struct file *dst_file,
+			 loff_t off, size_t len, loff_t dstoff);
 
 #ifdef CONFIG_BLOCK
 typedef void (dio_submit_t)(int rw, struct bio *bio, struct inode *inode,
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 9b964a5..ac7f1c5 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -39,6 +39,13 @@
 #define RENAME_EXCHANGE		(1 << 1)	/* Exchange source and dest */
 #define RENAME_WHITEOUT		(1 << 2)	/* Whiteout source */
 
+struct file_clone_range {
+	__s64 src_fd;
+	__u64 src_offset;
+	__u64 src_length;
+	__u64 dest_offset;
+};
+
 struct fstrim_range {
 	__u64 start;
 	__u64 len;
@@ -159,6 +166,8 @@ struct inodes_stat_t {
 #define FIFREEZE	_IOWR('X', 119, int)	/* Freeze */
 #define FITHAW		_IOWR('X', 120, int)	/* Thaw */
 #define FITRIM		_IOWR('X', 121, struct fstrim_range)	/* Trim */
+#define FICLONE		_IOW(0x94, 9, int)	/* Clone */
+#define FICLONERANGE	_IOW(0x94, 13, struct file_clone_range)	/* Clone range */
 
 #define	FS_IOC_GETFLAGS			_IOR('f', 1, long)
 #define	FS_IOC_SETFLAGS			_IOW('f', 2, long)
-- 
1.8.3.1