[Devel] Re: [PATCH 1/5] Add _ckpt_read_hdr_type() helper

[Oren Laadan]

Dan Smith wrote:
> This helper function gives us a way to read a header object and the
> subsequent payload from the checkpoint stream directly into our own
> buffer.  This is used by the net/checkpoint.c code to read skb's
> without a memcpy().
> 
> Signed-off-by: Dan Smith <danms at us.ibm.com>
> ---
>  checkpoint/restart.c       |   36 ++++++++++++++++++++++++++++++++++--
>  include/linux/checkpoint.h |    4 ++++
>  2 files changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/checkpoint/restart.c b/checkpoint/restart.c
> index 677f030..5cbe491 100644
> --- a/checkpoint/restart.c
> +++ b/checkpoint/restart.c
> @@ -178,6 +178,38 @@ int _ckpt_read_string(struct ckpt_ctx *ctx, void *ptr, int len)
>  }
>  
>  /**
> + * _ckpt_read_hdr_type - read a header record and check the type
> + * @ctx: checkpoint context
> + * @h: provided header buffer (returned)
> + * @type: optional type, 0 to ignore
> + *
> + * Returns the size of the payload to follow or negative on error
> + */
> +int _ckpt_read_hdr_type(struct ckpt_ctx *ctx, struct ckpt_hdr *h, int type)
> +{
> +	int ret;
> +
> +	ret = ckpt_kread(ctx, h, sizeof(*h));
> +	if (ret < 0)
> +		return ret;
> +	else if (type && h->type != type)
> +		return -EINVAL;
> +	else
> +		return h->len - sizeof(*h);
> +}

See commit 9efd630c26be10aee66a7d124f57b6227257a47e in ckpt-v17-dev -
it modifies _ckpt_read_obj_type() to do what you want. It is used in
the following commit f8b21d1fb5a162ae4ae8460dbde1981cf5df36a0 in
restore_pipe().

> +
> +/**
> + * _ckpt_read_payload - read the payload associated with a recent header read
> + * @ctx: checkpoint_context
> + * @h: header returned from _ckpt_read_hdr_type()
> + * @buffer: pre-allocated buffer to store payload
> + */
> +int _ckpt_read_payload(struct ckpt_ctx *ctx, struct ckpt_hdr *h, void *buffer)
> +{
> +	return ckpt_kread(ctx, buffer, h->len - sizeof(*h));
> +}

Since _ckpt_read_obj_type() now returns the actual payload length,
you change the prototype to accept @len instead of @h.

Nit: rename to _ckpt_read_obj_payload() or _ckpt_read_obj_data() to
maintain existing naming convention ?

(Or use ckpt_kread() directly ...)

Oren.


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