ring.h: introduce macros to handle monodirectional rings with multiple req sizes
PATCH v2 1/1 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.
---
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-v5
--- xen/include/public/io/ring.h | 114 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 114 insertions(+)
xen/include/public/io/ring.h +114 -0
@@ -313,6 +313,120 @@ 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, +* 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 (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 || \ + sizeof(*h) <= ring_size - *masked_cons) { \ + memcpy(h, buf + *masked_cons, sizeof(*h)); \ + } else { \ + memcpy(h, buf + *masked_cons, ring_size - *masked_cons); \ + memcpy((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(char *buf, \ + RING_IDX *masked_prod, RING_IDX *masked_cons, \ + RING_IDX ring_size, 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, (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 */ \ +}; \ + \ +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 - prod); \ +return size; \ +}; +#endif /* __XEN_PUBLIC_IO_RING_H__ */ /*
Signature · 7 lines
1.9.1 _______________________________________________ Xen-devel mailing list [email protected] https://lists.xen.org/xen-devel
Review
Quoted 3 lines
Quoted 1 line
Quoted 1 line · On 21.02.17 at 02:32, <[email protected]> wrote:
(quoted diff) +2
-0+static inline void name##_read_packet(char *buf, \ + RING_IDX *masked_prod, RING_IDX *masked_cons, \
The const/indirection problems is still there.
xen/include/public/io/ring.h typedef struct __name##_back_ring __name##_back_ring_t · line 379
Quoted 3 lines
xen/include/public/io/ring.h +3
-0+static inline void name##_write_packet(char *buf, \ +RING_IDX *masked_prod,RING_IDX *masked_cons, \ +RING_IDX ring_size,packet_t *h) { \
Same here - it being a pointer now, the last parameter should then be a pointer to const (and you shouldn't cast away constness below).
xen/include/public/io/ring.h typedef struct __name##_back_ring __name##_back_ring_t · line 428
Quoted 12 lines
xen/include/public/io/ring.h +12
-0+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[]; \ +};
The use of a variable sized array here should also be mentioned as an exception from the C89-compatibility rule in the description.
Jan
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Quoted 5 lines · Jan Beulich
Review
Quoted 3 lines
Quoted 1 line
Quoted 1 line · On 21.02.17 at 02:32, <[email protected]> wrote:
(quoted diff) +2
-0+static inline void name##_read_packet(char *buf, \ + RING_IDX *masked_prod, RING_IDX *masked_cons, \The const/indirection problems is still there.
I'll fix
Quoted 6 lines
xen/include/public/io/ring.h typedef struct __name##_back_ring __name##_back_ring_t · line 379
Quoted 3 lines
xen/include/public/io/ring.h +3
-0+static inline void name##_write_packet(char *buf, \ +RING_IDX *masked_prod,RING_IDX *masked_cons, \ +RING_IDX ring_size,packet_t *h) { \Same here - it being a pointer now, the last parameter should then be a pointer to const (and you shouldn't cast away constness below).
OK
Quoted 7 lines
Quoted 7 lines
xen/include/public/io/ring.h +7
-0+struct name##_data_intf { \ +RING_IDX in_cons, in_prod; \ + \ +uint8_t pad1[56 ]; \ + \ +RING_IDX out_cons, out_prod; \ + \
Quoted 8 lines
xen/include/public/io/ring.h typedef struct __name##_back_ring __name##_back_ring_t · line 428
Quoted 5 lines
xen/include/public/io/ring.h +5
-0+uint8_t pad2[56 ]; \ + \ +RING_IDX ring_order; \ +grant_ref_t ref[]; \ +};The use of a variable sized array here should also be mentioned as an exception from the C89-compatibility rule in the description.
Makes sense
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