[PATCH] Btrfs/send: sparse and pre-allocated file support for, btrfs-send mechanism

[Chen Yang <chenyang.fnst@cn.fujitsu.com>]

From: Chen Yang <chenyang.fnst@cn.fujitsu.com>
Date: Wed, 23 Jan 2013 11:21:51 +0800
Subject: [PATCH] Btrfs/send: sparse and pre-allocated file support for
 btrfs-send mechanism

When sending a file with sparse or pre-allocated part,
these parts will be sent as ZERO streams, and it's unnecessary.

There are two ways to improve this, one is just skip the EMPTY parts,
and the other one is to add a punch command to send, when an EMPTY parts
was detected. But considering a case of incremental sends, if we choose
the first one, when a hole got punched into the file after the initial
send, the data will be unchanged on the receiving side when received
incrementally. So the second choice is right.

Signed-off-by: Cheng Yang <chenyang.fnst@cn.fujitsu.com>
---
 fs/btrfs/send.c |   60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 fs/btrfs/send.h |    3 +-
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 5445454..31e9aef 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -3585,6 +3585,52 @@ out:
 	return ret;
 }
 
+static int send_punch(struct send_ctx *sctx, u64 offset, u32 len)
+{
+	int ret = 0;
+	struct fs_path *p;
+	mm_segment_t old_fs;
+
+	p = fs_path_alloc(sctx);
+	if (!p)
+		return -ENOMEM;
+
+	/*
+	 * vfs normally only accepts user space buffers for security reasons.
+	 * we only read from the file and also only provide the read_buf buffer
+	 * to vfs. As this buffer does not come from a user space call, it's
+	 * ok to temporary allow kernel space buffers.
+	 */
+	old_fs = get_fs();
+	set_fs(KERNEL_DS);
+
+verbose_printk("btrfs: send_fallocate offset=%llu, len=%d\n", offset, len);
+
+	ret = open_cur_inode_file(sctx);
+	if (ret < 0)
+		goto out;
+
+	ret = begin_cmd(sctx, BTRFS_SEND_C_PUNCH);
+	if (ret < 0)
+		goto out;
+
+	ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
+	if (ret < 0)
+		goto out;
+
+	TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
+	TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
+	TLV_PUT_U64(sctx, BTRFS_SEND_A_SIZE, len);
+
+	ret = send_cmd(sctx);
+
+tlv_put_failure:
+out:
+	fs_path_free(sctx, p);
+	set_fs(old_fs);
+	return ret;
+}
+
 /*
  * Read some bytes from the current inode/file and send a write command to
  * user space.
@@ -3718,6 +3764,7 @@ static int send_write_or_clone(struct send_ctx *sctx,
 	u64 pos = 0;
 	u64 len;
 	u32 l;
+	u64 bytenr;
 	u8 type;
 
 	ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
@@ -3731,8 +3778,19 @@ static int send_write_or_clone(struct send_ctx *sctx,
 		 * sure to send the whole thing
 		 */
 		len = PAGE_CACHE_ALIGN(len);
-	} else {
+	} else if (type == BTRFS_FILE_EXTENT_REG) {
 		len = btrfs_file_extent_num_bytes(path->nodes[0], ei);
+		bytenr = btrfs_file_extent_disk_bytenr(path->nodes[0], ei);
+		if (bytenr == 0) {
+			ret = send_punch(sctx, offset, len);
+			goto out;
+		}
+	} else if (type == BTRFS_FILE_EXTENT_PREALLOC) {
+		len = btrfs_file_extent_num_bytes(path->nodes[0], ei);
+		ret = send_punch(sctx, offset, len);
+		goto out;
+	} else {
+		BUG();
 	}
 
 	if (offset + len > sctx->cur_inode_size)
diff --git a/fs/btrfs/send.h b/fs/btrfs/send.h
index 1bf4f32..659ac8f 100644
--- a/fs/btrfs/send.h
+++ b/fs/btrfs/send.h
@@ -20,7 +20,7 @@
 #include "ctree.h"
 
 #define BTRFS_SEND_STREAM_MAGIC "btrfs-stream"
-#define BTRFS_SEND_STREAM_VERSION 1
+#define BTRFS_SEND_STREAM_VERSION 2
 
 #define BTRFS_SEND_BUF_SIZE (1024 * 64)
 #define BTRFS_SEND_READ_SIZE (1024 * 48)
@@ -80,6 +80,7 @@ enum btrfs_send_cmd {
 	BTRFS_SEND_C_WRITE,
 	BTRFS_SEND_C_CLONE,
 
+	BTRFS_SEND_C_PUNCH,
 	BTRFS_SEND_C_TRUNCATE,
 	BTRFS_SEND_C_CHMOD,
 	BTRFS_SEND_C_CHOWN,
-- 
1.7.7.6