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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 1/3] [RESEND] ring.h: introduce macros to handle monodirectional rings with multiple req sizes
On Mon, Mar 20, 2017 at 10:49:21AM -0700, Stefano Stabellini wrote:
> This patch introduces macros, structs and functions to handle rings in
> the format described by docs/misc/pvcalls.markdown and
> docs/misc/9pfs.markdown. The index page (struct __name##_data_intf)
> contains the indexes and the grant refs to setup two rings.
>
> Indexes page
> +----------------------+
> |@0 $NAME_data_intf: |
> |@76: ring_order = 1 |
> |@80: ref[0]+ |
> |@84: ref[1]+ |
> | | |
> | | |
> +----------------------+
> |
> v (data ring)
> +-------+-----------+
> | @0->4098: in |
4095
> | ref[0] |
> |-------------------|
> | @4099->8196: out |
4096->8191 ?
> | ref[1] |
> +-------------------+
>
> $NAME_read_packet and $NAME_write_packet are provided to read or write
> any data struct from/to the ring. In pvcalls, they are unused. In xen
> 9pfs, they are used to read or write the 9pfs header. In other protocols
> they could be used to read/write the whole request structure. See
> docs/misc/9pfs.markdown:Ring Usage to learn how to check how much data
> is on the ring, and how to handle notifications.
>
> There is a ring_size parameter to most functions so that protocols using
> these macros don't have to have a statically defined ring order at build
> time. In pvcalls for example, each new ring could have a different
> order.
>
> These macros don't help you share the indexes page or the event channels
> needed for notifications. You can do that with other out of band
> mechanisms, such as xenstore or another ring.
>
> It is not possible to use a macro to define another macro with a
> variable name. For this reason, this patch introduces static inline
> functions instead, that are not C89 compliant. Additionally, the macro
> defines a struct with a variable sized array, which is also not C89
> compliant.
>
> Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> CC: konrad.wilk@xxxxxxxxxx
>
> ---
> Changes in v4:
> - remove packet_t, use void* and size instead
>
> Changes in v3:
> - mention C89 compliance breakages
> - constify parameters
> - use unsigned chars for buffers
> - add two macros, one doesn't define the struct
>
> Changes in v2:
> - fix typo
> - remove leading underscores from names
> - use UL
> - do not parenthesize parameters
> - code readability improvements
>
> Give a look at the following branch to see how they are used with
> pvcalls and xen-9pfs (the drivers are still work in progress):
>
> git://git.kernel.org/pub/scm/linux/kernel/git/sstabellini/xen.git
> 9pfs-async-v7
> ---
> ---
> xen/include/public/io/ring.h | 131
> +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 131 insertions(+)
>
> diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
> index 801c0da..8ac9ca3 100644
> --- a/xen/include/public/io/ring.h
> +++ b/xen/include/public/io/ring.h
> @@ -313,6 +313,137 @@ typedef struct __name##_back_ring __name##_back_ring_t
> (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
> } while (0)
>
> +
> +/*
> + * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
> + * functions to check if there is data on the ring, and to read and
> + * write to them.
> + *
> + * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
> + * does not define the indexes page. As different protocols can have
> + * extensions to the basic format, this macro allow them to define their
> + * own struct.
> + *
> + * XEN_FLEX_RING_SIZE
> + * Convenience macro to calculate the size of one of the two rings
> + * from the overall order.
> + *
> + * $NAME_mask
> + * Function to apply the size mask to an index, to reduce the index
> + * within the range [0-size].
> + *
> + * $NAME_read_packet
> + * Function to read data from the ring. The amount of data to read is
> + * specified by the "size" argument.
> + *
> + * $NAME_write_packet
> + * Function to write data to the ring. The amount of data to write is
> + * specified by the "size" argument.
> + *
> + * $NAME_get_ring_ptr
> + * Convenience function that returns a pointer to read/write to the
> + * ring at the right location.
> + *
> + * $NAME_data_intf
> + * Indexes page, shared between frontend and backend. It also
> + * contains the array of grant refs.
> + *
> + * $NAME_queued
> + * Function to calculate how many bytes are currently on the ring,
> + * ready to be read. It can also be used to calculate how much free
> + * space is currently on the ring (ring_size - $NAME_queued()).
> + */
> +#define XEN_FLEX_RING_SIZE(order)
> \
> + (1UL << (order + PAGE_SHIFT - 1))
> +
> +#define DEFINE_XEN_FLEX_RING_AND_INTF(name)
> \
> +struct name##_data_intf {
> \
> + RING_IDX in_cons, in_prod;
> \
> +
> \
> + uint8_t pad1[56];
> \
> +
> \
> + RING_IDX out_cons, out_prod;
> \
> +
> \
> + uint8_t pad2[56];
> \
> +
> \
> + RING_IDX ring_order;
> \
> + grant_ref_t ref[];
> \
> +};
> \
> +DEFINE_XEN_FLEX_RING(name);
Should this macro #define DEFINE_XEN_FLEX_RING_AND_INTF be below the macro
DEFINE_XEN_FLEX_RING?
As the DEFINE_XEN_FLEX_RING_AND_INTF uses the DEFINE_XEN_FLEX_RING?
> +
> +#define DEFINE_XEN_FLEX_RING(name)
> \
> +static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size)
> \
> +{
> \
> + return (idx & (ring_size - 1));
> \
Could you put () around ring_size and idx please.
> +}
> \
> +
> \
> +static inline RING_IDX name##_mask_order(RING_IDX idx, RING_IDX ring_order)
> \
> +{
> \
> + return (idx & (XEN_FLEX_RING_SIZE(ring_order) - 1));
> \
As well for idx here?
> +}
> \
> +
> \
> +static inline unsigned char* name##_get_ring_ptr(unsigned char *buf,
> \
> + RING_IDX idx,
> \
> + RING_IDX ring_order)
> \
> +{
> \
> + return buf + name##_mask_order(idx, ring_order);
> \
> +}
> \
> +
> \
> +static inline void name##_read_packet(const unsigned char *buf,
> \
> + RING_IDX masked_prod, RING_IDX *masked_cons,
> \
> + RING_IDX ring_size, void *opaque, size_t size) {
> \
How about anewline here
> + if (*masked_cons < masked_prod ||
> \
Any particular reason you are using an pointer to masked_cons?
And vice versa on the _write_packet function?
> + size <= ring_size - *masked_cons) {
> \
> + memcpy(opaque, buf + *masked_cons, size);
> \
> + } else {
> \
> + memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons);
> \
> + memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf,
> \
> + size - (ring_size - *masked_cons));
> \
> + }
> \
> + *masked_cons = name##_mask(*masked_cons + size, ring_size);
> \
> +}
> \
> +
> \
> +static inline void name##_write_packet(unsigned char *buf,
> \
> + RING_IDX *masked_prod, RING_IDX masked_cons,
> \
> + RING_IDX ring_size, const void *opaque, size_t size) {
> \
How about anewline here
> + if (*masked_prod < masked_cons ||
> \
> + size <= ring_size - *masked_prod) {
> \
> + memcpy(buf + *masked_prod, opaque, size);
> \
> + } else {
> \
> + memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod);
> \
> + memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod),
> \
> + size - (ring_size - *masked_prod));
> \
> + }
> \
> + *masked_prod = name##_mask(*masked_prod + size, ring_size);
> \
> +}
> \
> +
> \
> +struct name##_data {
> \
> + unsigned char *in; /* half of the allocation */
> \
> + unsigned char *out; /* half of the allocation */
> \
> +};
> \
> +
> \
> +
> \
> +static inline RING_IDX name##_queued(RING_IDX prod,
> \
> + RING_IDX cons, RING_IDX ring_size)
> \
> +{
> \
> + RING_IDX size;
> \
> +
> \
> + if (prod == cons)
> \
> + return 0;
> \
> +
> \
> + prod = name##_mask(prod, ring_size);
> \
> + cons = name##_mask(cons, ring_size);
> \
> +
> \
> + if (prod == cons)
> \
> + return ring_size;
> \
> +
> \
> + if (prod > cons)
> \
> + size = prod - cons;
> \
> + else
> \
> + size = ring_size - (cons - prod);
> \
> + return size;
> \
> +};
> +
> #endif /* __XEN_PUBLIC_IO_RING_H__ */
>
> /*
> --
> 1.9.1
>
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