From c2c71324ecb471c932bc1ff59e46ffcf82f274fc Mon Sep 17 00:00:00 2001 From: Stefan Behrens Date: Wed, 10 Apr 2013 17:10:52 +0000 Subject: [PATCH] Btrfs: allow omitting stream header and end-cmd for btrfs send Two new flags are added to allow omitting the stream header and the end command for btrfs send streams. This is used in cases where you send multiple snapshots back-to-back in one stream. This used to be encoded like this (with 2 snapshots in this example): + + + + + + EOF The new format (if the two new flags are used) is this one: + + + Note that the currently existing receivers treat only as an indication that a new is following. This means, you can just skip the sequence without loosing compatibility. As long as an EOF is following, the currently existing receivers handle the new format (if the two new flags are used) exactly as the old one. So what is the benefit of this change? The goal is to be able to use a single stream (one TCP connection) to multiplex a request/response handshake plus Btrfs send streams, all in the same stream. In this case you cannot evaluate an EOF condition as an end of the Btrfs send stream. You need something else, and the is just perfect for this purpose. The summary is: The format change is driven by the need to send several Btrfs send streams over a single TCP connections, with the ability for a repeated request/response handshake in the middle. And this format change does not break any existing tool, it is completely compatible. You could compare the old behaviour of the Btrfs send stream to the one of ftp where you need a seperate request/response channel and newly opened data transfer channels for each file, while the new behaviour is more like http using a single stream for everything. Signed-off-by: Stefan Behrens Signed-off-by: Josef Bacik --- fs/btrfs/send.c | 24 ++++++++++++++---------- include/uapi/linux/btrfs.h | 20 +++++++++++++++++++- 2 files changed, 33 insertions(+), 11 deletions(-) diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c index c85e7c6..e0c69a1 100644 --- a/fs/btrfs/send.c +++ b/fs/btrfs/send.c @@ -4529,9 +4529,11 @@ static int send_subvol(struct send_ctx *sctx) { int ret; - ret = send_header(sctx); - if (ret < 0) - goto out; + if (!(sctx->flags & BTRFS_SEND_FLAG_OMIT_STREAM_HEADER)) { + ret = send_header(sctx); + if (ret < 0) + goto out; + } ret = send_subvol_begin(sctx); if (ret < 0) @@ -4593,7 +4595,7 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_) goto out; } - if (arg->flags & ~BTRFS_SEND_FLAG_NO_FILE_DATA) { + if (arg->flags & ~BTRFS_SEND_FLAG_MASK) { ret = -EINVAL; goto out; } @@ -4704,12 +4706,14 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_) if (ret < 0) goto out; - ret = begin_cmd(sctx, BTRFS_SEND_C_END); - if (ret < 0) - goto out; - ret = send_cmd(sctx); - if (ret < 0) - goto out; + if (!(sctx->flags & BTRFS_SEND_FLAG_OMIT_END_CMD)) { + ret = begin_cmd(sctx, BTRFS_SEND_C_END); + if (ret < 0) + goto out; + ret = send_cmd(sctx); + if (ret < 0) + goto out; + } out: kfree(arg); diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h index fa3a5f9..5e39e85 100644 --- a/include/uapi/linux/btrfs.h +++ b/include/uapi/linux/btrfs.h @@ -412,7 +412,25 @@ struct btrfs_ioctl_received_subvol_args { * search of clone sources doesn't find an extent. UPDATE_EXTENT * commands will be sent instead of WRITE commands. */ -#define BTRFS_SEND_FLAG_NO_FILE_DATA 0x1 +#define BTRFS_SEND_FLAG_NO_FILE_DATA 0x1 + +/* + * Do not add the leading stream header. Used when multiple snapshots + * are sent back to back. + */ +#define BTRFS_SEND_FLAG_OMIT_STREAM_HEADER 0x2 + +/* + * Omit the command at the end of the stream that indicated the end + * of the stream. This option is used when multiple snapshots are + * sent back to back. + */ +#define BTRFS_SEND_FLAG_OMIT_END_CMD 0x4 + +#define BTRFS_SEND_FLAG_MASK \ + (BTRFS_SEND_FLAG_NO_FILE_DATA | \ + BTRFS_SEND_FLAG_OMIT_STREAM_HEADER | \ + BTRFS_SEND_FLAG_OMIT_END_CMD) struct btrfs_ioctl_send_args { __s64 send_fd; /* in */ -- 2.7.4