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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH] ring.h: introduce macros to handle monodirectional rings with multiple req sizes
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.
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
---
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-v4
---
---
xen/include/public/io/ring.h | 122 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 122 insertions(+)
diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
index 801c0da..ca9a8f0 100644
--- a/xen/include/public/io/ring.h
+++ b/xen/include/public/io/ring.h
@@ -313,6 +313,128 @@ typedef struct __name##_back_ring __name##_back_ring_t
(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
} while (0)
+
+/*
+ * DEFINE_XEN_FLEX_RING defines two monodirectional rings and functions
+ * to check if there is data on the ring, and to read and write to them.
+ *
+ * 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. Different protocols can have
+ * extensions to the basic format, in such cases please define your
+ * own data_intf struct.
+ *
+ * $NAME_queued
+ * Function to calculate how many bytes are currently on the ring,
+ * read 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) \
+ ((1 << ((__order) + XEN_PAGE_SHIFT)) / 2)
+
+#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(char *buf, \
+ RING_IDX *masked_prod, RING_IDX *masked_cons, \
+ RING_IDX ring_size, __packet_t *h) { \
+ if (*masked_cons < *masked_prod) { \
+ memcpy(h, buf + *masked_cons, sizeof(*h)); \
+ } else { \
+ if (sizeof(*h) > ring_size - *masked_cons) { \
+ memcpy(h, buf + *masked_cons, ring_size - *masked_cons); \
+ memcpy((char *)h + ring_size - *masked_cons, buf, \
+ sizeof(*h) - (ring_size - *masked_cons)); \
+ } else { \
+ memcpy(h, buf + *masked_cons, sizeof(*h)); \
+ } \
+ } \
+ *masked_cons = __name##_mask(*masked_cons + sizeof(*h), ring_size); \
+} \
+ \
+static inline void __name##_write_packet(char *buf, \
+ RING_IDX *masked_prod, RING_IDX *masked_cons, \
+ RING_IDX ring_size, __packet_t h) { \
+ if (*masked_prod < *masked_cons) { \
+ memcpy(buf + *masked_prod, &h, sizeof(h)); \
+ } else { \
+ if (sizeof(h) > ring_size - *masked_prod) { \
+ memcpy(buf + *masked_prod, &h, ring_size - *masked_prod); \
+ memcpy(buf, (char *)(&h) + (ring_size - *masked_prod), \
+ sizeof(h) - (ring_size - *masked_prod)); \
+ } else { \
+ memcpy(buf + *masked_prod, &h, sizeof(h)); \
+ } \
+ } \
+ *masked_prod = __name##_mask(*masked_prod + sizeof(h), ring_size); \
+} \
+ \
+struct __name##_data { \
+ char *in; /* half of the allocation */ \
+ char *out; /* half of the allocation */ \
+}; \
+ \
+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[]; \
+}; \
+ \
+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; \
+ size += prod; \
+ } \
+ return size; \
+};
+
#endif /* __XEN_PUBLIC_IO_RING_H__ */
/*
--
1.9.1
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