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Re: [Xen-devel] [PATCH v3] ring.h: introduce macros to handle monodirectional rings with multiple req sizes
Hi, Stefano, Jan!
1. Stefano, are you still NOT considering adding
functionality to avoid memory copying? We discussed
this a little bit here [1].
2. Will you also provide macros/inlines for fixed sized packets?
So, others do not reinvent the wheel again on top of your code.
3. C89 - Jan, we discussed that a bit for zero-sized arrays [2]
and empty structures [3]. So, then we came to a conclusion that
breakage is not acceptable, but now I see that you have changed
your mind? (Please correct me if I got it wrong). The reason I am
bringing this back to life is that sndif and displif protocols
use grefs[1] construct, while originally I was about to avoid that "1".
So, as now Stefano introduces *grant_ref_t ref[];* I would also
like to change sndif/displif to use the same. Do you think it can be
done this time?
Thank you,
Oleksandr
[1] https://marc.info/?l=xen-devel&m=148356651811001&w=2
[2] https://marc.info/?l=xen-devel&m=148006553214656&w=2
[3] https://marc.info/?l=xen-devel&m=148000448701946&w=2
On 02/22/2017 01:25 AM, 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 |
| ref[0] |
|-------------------|
| @4099->8196: out |
| 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
CC: andr2000@xxxxxxxxx
CC: oleksandr_andrushchenko@xxxxxxxx
CC: andrii.anisov@xxxxxxxxx
CC: vlad.babchuk@xxxxxxxxx
CC: al1img@xxxxxxxxx
CC: joculator@xxxxxxxxx
---
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-v6
---
---
xen/include/public/io/ring.h | 120 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 120 insertions(+)
diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
index 801c0da..4d36f06 100644
--- a/xen/include/public/io/ring.h
+++ b/xen/include/public/io/ring.h
@@ -313,6 +313,126 @@ 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 a defined amount of data from the ring. The amount
+ * of data read is sizeof(__packet_t).
+ *
+ * $NAME_write_packet
+ * Function to write a defined amount of data to the ring. The amount
+ * of data to write is sizeof(__packet_t).
+ *
+ * $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, packet_t) \
+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, packet_t);
+
+#define DEFINE_XEN_FLEX_RING(name, packet_t) \
+static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size) \
+{ \
+ return (idx & (ring_size - 1)); \
+} \
+ \
+static inline RING_IDX name##_mask_order(RING_IDX idx, RING_IDX ring_order) \
+{ \
+ return (idx & (XEN_FLEX_RING_SIZE(ring_order) - 1)); \
+} \
+ \
+static inline void name##_read_packet(const unsigned char *buf, \
+ RING_IDX masked_prod, RING_IDX *masked_cons, \
+ RING_IDX ring_size, packet_t *h) { \
+ if (*masked_cons < masked_prod || \
+ sizeof(*h) <= ring_size - *masked_cons) { \
+ memcpy(h, buf + *masked_cons, sizeof(*h)); \
+ } else { \
+ memcpy(h, buf + *masked_cons, ring_size - *masked_cons); \
+ memcpy((unsigned char *)h + ring_size - *masked_cons, buf, \
+ sizeof(*h) - (ring_size - *masked_cons)); \
+ } \
+ *masked_cons = name##_mask(*masked_cons + sizeof(*h), ring_size); \
+} \
+ \
+static inline void name##_write_packet(unsigned char *buf, \
+ RING_IDX *masked_prod, RING_IDX masked_cons, \
+ RING_IDX ring_size, const packet_t *h) { \
+ if (*masked_prod < masked_cons || \
+ sizeof(*h) <= ring_size - *masked_prod) { \
+ memcpy(buf + *masked_prod, h, sizeof(*h)); \
+ } else { \
+ memcpy(buf + *masked_prod, h, ring_size - *masked_prod); \
+ memcpy(buf, (unsigned char *)h + (ring_size - *masked_prod), \
+ sizeof(*h) - (ring_size - *masked_prod)); \
+ } \
+ *masked_prod = name##_mask(*masked_prod + sizeof(*h), 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__ */
/*
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