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Re: [Xen-devel] [PATCH v8 1/4] ring.h: introduce macros to handle monodirectional rings with multiple req sizes



On Fri, Mar 31, 2017 at 12:15:16PM -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->4095: in     |
>                    |  ref[0]           |
>                    |-------------------|
>                    |  @4096->8191: 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: JBeulich@xxxxxxxx
> ---
>  xen/include/public/io/ring.h | 151 
> +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 151 insertions(+)
> 
> diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
> index 801c0da..7b7794c 100644
> --- a/xen/include/public/io/ring.h
> +++ b/xen/include/public/io/ring.h
> @@ -27,6 +27,21 @@
>  #ifndef __XEN_PUBLIC_IO_RING_H__
>  #define __XEN_PUBLIC_IO_RING_H__
>  
> +/*
> + * When #include'ing this header, you need to provide the following
> + * declaration upfront:
> + * - standard integers types (uint8_t, uint16_t, etc)
> + * They are provided by stdint.h of the standard headers.
> + *
> + * In addition, if you intend to use the FLEX macros, you also need to
> + * provide the following, before invoking the FLEX macros:
> + * - size_t
> + * - memcpy
> + * - grant_ref_t
> + * These declarations are provided by string.h of the standard headers,
> + * and grant_table.h from the Xen public headers.
> + */
> +
>  #include "../xen-compat.h"
>  
>  #if __XEN_INTERFACE_VERSION__ < 0x00030208
> @@ -313,6 +328,142 @@ 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()).

s/ring_size/XEN_FLEX_RING_SIZE/ ?

> + */
> +
> +#define XEN_PAGE_SHIFT 12

Perhaps a comment explaining why you have that? It looks very architecture
dependent?

Or perhaps you could do with

#ifndef XEN_PAGE_SHIFT
/*
 * Hypercall interface only supports only 4Kb page unless the architecture
 * overrides it.
 */
#define XEN_PAGE_SHIFT 12
#endif

?

> +#define XEN_FLEX_RING_SIZE(order)                                            
>  \
> +    (1UL << ((order) + XEN_PAGE_SHIFT - 1))
> +
> +#define DEFINE_XEN_FLEX_RING(name)                                           
>  \
> +static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size)         
>  \
> +{                                                                            
>  \
> +    return idx & (ring_size - 1);                                            
>  \
> +}                                                                            
>  \
> +                                                                             
>  \
> +static inline unsigned char *name##_get_ring_ptr(unsigned char *buf,         
>  \
> +                                                 RING_IDX idx,               
>  \
> +                                                 RING_IDX ring_size)         
>  \
> +{                                                                            
>  \
> +    return buf + name##_mask(idx, ring_size);                                
>  \
> +}                                                                            
>  \
> +                                                                             
>  \
> +static inline void name##_read_packet(void *opaque,                          
>  \
> +                                      const unsigned char *buf,              
>  \
> +                                      size_t size,                           
>  \
> +                                      RING_IDX masked_prod,                  
>  \
> +                                      RING_IDX *masked_cons,                 
>  \
> +                                      RING_IDX ring_size)                    
>  \
> +{                                                                            
>  \
> +    if (*masked_cons < masked_prod ||                                        
>  \
> +            size <= ring_size - *masked_cons) {                              
>  \

'size <= ..' is not aligned here while it is in _write_packet?

Besides that it looks fine to me.

> +        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,                   
>  \
> +                                       const void *opaque,                   
>  \
> +                                       size_t size,                          
>  \
> +                                       RING_IDX *masked_prod,                
>  \
> +                                       RING_IDX masked_cons,                 
>  \
> +                                       RING_IDX ring_size)                   
>  \
> +{                                                                            
>  \
> +    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);              
>  \
> +}                                                                            
>  \
> +                                                                             
>  \
> +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;                                                             
>  \
> +}                                                                            
>  \
> +                                                                             
>  \
> +struct name##_data {                                                         
>  \
> +    unsigned char *in; /* half of the allocation */                          
>  \
> +    unsigned char *out; /* half of the allocation */                         
>  \
> +}
> +
> +#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)
> +
>  #endif /* __XEN_PUBLIC_IO_RING_H__ */
>  
>  /*
> -- 
> 1.9.1
> 

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