Re: [PATCH v11 10/14] btrfs: add send stream v2 definitions

[Nikolay Borisov <nborisov@suse.com>]

On 1.09.21 г. 20:01, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> This adds the definitions of the new commands for send stream version 2
> and their respective attributes: fallocate, FS_IOC_SETFLAGS (a.k.a.
> chattr), and encoded writes. It also documents two changes to the send
> stream format in v2: the receiver shouldn't assume a maximum command
> size, and the DATA attribute is encoded differently to allow for writes
> larger than 64k. These will be implemented in subsequent changes, and
> then the ioctl will accept the new flags.
> 
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
>  fs/btrfs/send.c            |  2 +-
>  fs/btrfs/send.h            | 30 +++++++++++++++++++++++++++++-
>  include/uapi/linux/btrfs.h | 13 +++++++++++++
>  3 files changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
> index afdcbe7844e0..2ec07943f173 100644
> --- a/fs/btrfs/send.c
> +++ b/fs/btrfs/send.c
> @@ -7287,7 +7287,7 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
>  
>  	sctx->clone_roots_cnt = arg->clone_sources_count;
>  
> -	sctx->send_max_size = BTRFS_SEND_BUF_SIZE;
> +	sctx->send_max_size = BTRFS_SEND_BUF_SIZE_V1;
>  	sctx->send_buf = kvmalloc(sctx->send_max_size, GFP_KERNEL);
>  	if (!sctx->send_buf) {
>  		ret = -ENOMEM;
> diff --git a/fs/btrfs/send.h b/fs/btrfs/send.h
> index de91488b7cd0..9f4f7b96b1eb 100644
> --- a/fs/btrfs/send.h
> +++ b/fs/btrfs/send.h
> @@ -12,7 +12,11 @@
>  #define BTRFS_SEND_STREAM_MAGIC "btrfs-stream"
>  #define BTRFS_SEND_STREAM_VERSION 1
>  
> -#define BTRFS_SEND_BUF_SIZE SZ_64K
> +/*
> + * In send stream v1, no command is larger than 64k. In send stream v2, no limit
> + * should be assumed.
> + */
> +#define BTRFS_SEND_BUF_SIZE_V1 SZ_64K
>  
>  enum btrfs_tlv_type {
>  	BTRFS_TLV_U8,
> @@ -76,6 +80,13 @@ enum btrfs_send_cmd {
>  
>  	BTRFS_SEND_C_END,
>  	BTRFS_SEND_C_UPDATE_EXTENT,
> +
> +	/* The following commands were added in send stream v2. */
> +
> +	BTRFS_SEND_C_FALLOCATE,
> +	BTRFS_SEND_C_SETFLAGS,
> +	BTRFS_SEND_C_ENCODED_WRITE,
> +
>  	__BTRFS_SEND_C_MAX,
>  };
>  #define BTRFS_SEND_C_MAX (__BTRFS_SEND_C_MAX - 1)
> @@ -106,6 +117,11 @@ enum {
>  	BTRFS_SEND_A_PATH_LINK,
>  
>  	BTRFS_SEND_A_FILE_OFFSET,
> +	/*
> +	 * In send stream v2, this attribute is special: it must be the last
> +	 * attribute in a command, its header contains only the type, and its
> +	 * length is implicitly the remaining length of the command.
> +	 */
>  	BTRFS_SEND_A_DATA,

Now that I think more about this, it would be best if this logic is
actually codified in the code. I.e first set of SEND_A_DATA would set
some bool/flag in the sctx and subsequent calls would be able to
ASSERT/WARN ?