Re: [Xen-devel] [PATCH XTF v4] Implement pv_read_some

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 24/07/17 07:24, Felix Schmoll wrote:
> Implement reading from PV console. Making use of polling.
>
> Signed-off-by: Felix Schmoll <eggi.innovations@xxxxxxxxx>
>
> ---
> Changed since v3:
>  * Add to comment: read function blocks if no data available
> ---
>  common/console.c      | 26 ++++++++++++++++++++++++++
>  include/xtf/console.h |  2 ++
>  2 files changed, 28 insertions(+)
>
> diff --git a/common/console.c b/common/console.c
> index 7cb2361..b1a35f4 100644
> --- a/common/console.c
> +++ b/common/console.c
> @@ -46,6 +46,32 @@ static size_t pv_console_write_some(const char *buf, 
> size_t len)
>  }
>  
>  /*
> + * Read out data from the pv ring, either until buffer is filled or no
> + * more data are available. Might result in partial strings, depending
> + * on how xenconsoled passes in data.
> + *
> + * Will block if no data are available.
> + */
> +size_t pv_console_read_some(char *buf, size_t len)
> +{
> +    size_t s = 0;
> +    uint32_t cons, prod;
> +
> +    while ( !test_and_clear_bit(pv_evtchn, shared_info.evtchn_pending) ||
> +            (pv_ring->in_cons == pv_ring->in_prod) )
> +        hypercall_poll(pv_evtchn);
> +
> +    cons = pv_ring->in_cons, prod = LOAD_ACQUIRE(&pv_ring->in_prod);

Given the confusion this has caused on IRC, I'd prefer that the code was
explicit.  Is the following ok?

cons = pv_ring->in_cons;
prod = LOAD_ACQUIRE(&pv_ring->in_prod);

If so, I can fix up on commit.

~Andrew

> +
> +    while ( (s < len) && (0 < (prod - cons)) )
> +        buf[s++] = pv_ring->in[cons++ & (sizeof(pv_ring->in) - 1)];
> +
> +    STORE_RELEASE(&pv_ring->in_cons, cons);
> +
> +    return s;
> +}
> +
> +/*
>   * Write some data into the pv ring, synchronously waiting for all data to be
>   * consumed.
>   */
> diff --git a/include/xtf/console.h b/include/xtf/console.h
> index 2a93c06..caec790 100644
> --- a/include/xtf/console.h
> +++ b/include/xtf/console.h
> @@ -25,6 +25,8 @@ void init_pv_console(xencons_interface_t *ring,
>  void vprintk(const char *fmt, va_list args) __printf(1, 0);
>  void printk(const char *fmt, ...) __printf(1, 2);
>  
> +size_t pv_console_read_some(char *buf, size_t len);
> +
>  #endif /* XTF_CONSOLE_H */
>  
>  /*


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