[PATCH v3 8/9] vfs: copy_file_range() can do a pagecache copy with splice

[Anna Schumaker <Anna.Schumaker@netapp.com>]

The NFS server will need some kind offallback for filesystems that don't
have any kind of copy acceleration, and it should be generally useful to
have an in-kernel copy to avoid lots of switches between kernel and user
space.

I make this configurable by adding two new flags.  Users who only want a
reflink can pass COPY_FR_REFLINK, and users who want a full data copy can
pass COPY_FR_COPY.  The default (flags=0) means to first attempt a
reflink, but use the pagecache if that fails.

I moved the rw_verify_area() calls into the fallback code since some
filesystems can handle reflinking a large range.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
v3:
- Check that both filesystems have the same filesystem type
- Add COPY_FR_DEDUPE flag for Darrick
- Check that at most one flag is set at a time
---
 fs/read_write.c           | 61 +++++++++++++++++++++++++++++++----------------
 include/linux/copy.h      |  6 +++++
 include/uapi/linux/Kbuild |  1 +
 include/uapi/linux/copy.h |  8 +++++++
 4 files changed, 56 insertions(+), 20 deletions(-)
 create mode 100644 include/linux/copy.h
 create mode 100644 include/uapi/linux/copy.h

diff --git a/fs/read_write.c b/fs/read_write.c
index ee9fa37..a0fd9dc 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -7,6 +7,7 @@
 #include <linux/slab.h> 
 #include <linux/stat.h>
 #include <linux/fcntl.h>
+#include <linux/copy.h>
 #include <linux/file.h>
 #include <linux/uio.h>
 #include <linux/fsnotify.h>
@@ -1329,6 +1330,29 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
 }
 #endif
 
+static ssize_t vfs_copy_file_pagecache(struct file *file_in, loff_t pos_in,
+				       struct file *file_out, loff_t pos_out,
+				       size_t len)
+{
+	ssize_t ret;
+
+	ret = rw_verify_area(READ, file_in, &pos_in, len);
+	if (ret >= 0) {
+		len = ret;
+		ret = rw_verify_area(WRITE, file_out, &pos_out, len);
+		if (ret >= 0)
+			len = ret;
+	}
+	if (ret < 0)
+		return ret;
+
+	file_start_write(file_out);
+	ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out, len, 0);
+	file_end_write(file_out);
+
+	return ret;
+}
+
 /*
  * copy_file_range() differs from regular file read and write in that it
  * specifically allows return partial success.  When it does so is up to
@@ -1338,34 +1362,26 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 			    struct file *file_out, loff_t pos_out,
 			    size_t len, unsigned int flags)
 {
-	struct inode *inode_in;
-	struct inode *inode_out;
 	ssize_t ret;
 
-	if (flags)
+	/* Flags should only be used exclusively. */
+	if ((flags & COPY_FR_COPY) && (flags & ~COPY_FR_COPY))
 		return -EINVAL;
+	if ((flags & COPY_FR_REFLINK) && (flags & ~COPY_FR_REFLINK))
+		return -EINVAL;
+	if (flags & COPY_FR_DEDUPE)
+		return -EOPNOTSUPP;
 
-	/* copy_file_range allows full ssize_t len, ignoring MAX_RW_COUNT  */
-	ret = rw_verify_area(READ, file_in, &pos_in, len);
-	if (ret >= 0)
-		ret = rw_verify_area(WRITE, file_out, &pos_out, len);
-	if (ret < 0)
-		return ret;
+	/* Default behavior is to try both. */
+	if (flags == 0)
+		flags = COPY_FR_COPY | COPY_FR_REFLINK;
 
 	if (!(file_in->f_mode & FMODE_READ) ||
 	    !(file_out->f_mode & FMODE_WRITE) ||
 	    (file_out->f_flags & O_APPEND) ||
-	    !file_out->f_op || !file_out->f_op->copy_file_range)
+	    !file_out->f_op)
 		return -EBADF;
 
-	inode_in = file_inode(file_in);
-	inode_out = file_inode(file_out);
-
-	/* make sure offsets don't wrap and the input is inside i_size */
-	if (pos_in + len < pos_in || pos_out + len < pos_out ||
-	    pos_in + len > i_size_read(inode_in))
-		return -EINVAL;
-
 	if (len == 0)
 		return 0;
 
@@ -1373,8 +1389,13 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	if (ret)
 		return ret;
 
-	ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out, pos_out,
-					      len, flags);
+	ret = -EOPNOTSUPP;
+	if (file_out->f_op->copy_file_range && (file_in->f_op == file_out->f_op))
+		ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
+						      pos_out, len, flags);
+	if ((ret < 0) && (flags & COPY_FR_COPY))
+		ret = vfs_copy_file_pagecache(file_in, pos_in, file_out,
+					      pos_out, len);
 	if (ret > 0) {
 		fsnotify_access(file_in);
 		add_rchar(current, ret);
diff --git a/include/linux/copy.h b/include/linux/copy.h
new file mode 100644
index 0000000..fd54543
--- /dev/null
+++ b/include/linux/copy.h
@@ -0,0 +1,6 @@
+#ifndef _LINUX_COPY_H
+#define _LINUX_COPY_H
+
+#include <uapi/linux/copy.h>
+
+#endif /* _LINUX_COPY_H */
diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
index f7b2db4..faafd67 100644
--- a/include/uapi/linux/Kbuild
+++ b/include/uapi/linux/Kbuild
@@ -90,6 +90,7 @@ header-y += coda_psdev.h
 header-y += coff.h
 header-y += connector.h
 header-y += const.h
+header-y += copy.h
 header-y += cramfs_fs.h
 header-y += cuda.h
 header-y += cyclades.h
diff --git a/include/uapi/linux/copy.h b/include/uapi/linux/copy.h
new file mode 100644
index 0000000..6225838
--- /dev/null
+++ b/include/uapi/linux/copy.h
@@ -0,0 +1,8 @@
+#ifndef _UAPI_LINUX_COPY_H
+#define _UAPI_LINUX_COPY_H
+
+#define COPY_FR_COPY		(1 << 0)  /* Only do a pagecache copy.  */
+#define COPY_FR_REFLINK		(1 << 1)  /* Only make a reflink.       */
+#define COPY_FR_DEDUPE		(1 << 2)  /* Deduplicate file data.     */
+
+#endif /* _UAPI_LINUX_COPY_H */
-- 
2.5.3