/usr/include/rtai/rtai_scb.h is in librtai-dev 3.9.1-4.
This file is owned by root:root, with mode 0o644.
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* @ingroup shm
* @file
*
* SCB stand for Shared (memory) Circular Buffer. It is a non blocking
* implementation for just a single writer (producer) and reader
* (consumer) and, under such a constraint, it can be a specific
* substitute for RTAI mailboxes. There are other constraints that
* must be satisfied, so it cannot be a general substitute for the more
* flexible RTAI mailboxes. In fact it provides just functions
* corresponding to RTAI mailboxes non blocking atomic send/receive of
* messages, i.e. the equivalents of rt_mbx_send_if and
* rt_mbx_receive_if. Moreover the circular buffer size must be >= to
* the largest message to be sent/received. At least the double of the
* largest message to be sent/received is strongly recommended.
* Thus sending/receiving a message either succeeds of fails. However
* thanks to the use of shared memory it should be more efficient than
* mailboxes in atomic exchanges of messages from kernel to user space.
* So it is a good candidate for supporting drivers development.
*
* @author Paolo Mantegazza
*
* @note Copyright © 2004-2008 Paolo Mantegazza <mantegazza@aero.polimi.it>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#ifndef _RTAI_SCB_H
#define _RTAI_SCB_H
#include <rtai_shm.h>
#include <asm/rtai_atomic.h>
#define SCB ((void *)(scb))
#define SIZE ((volatile int *)scb)[-3]
#define FBYTE ((volatile int *)scb)[-2]
#define LBYTE ((volatile int *)scb)[-1]
#define HDRSIZ (3*sizeof(int))
struct task_struct;
#ifdef __KERNEL__
#define RTAI_SCB_PROTO(type, name, arglist) static inline type name arglist
#else
#define RTAI_SCB_PROTO RTAI_PROTO
#endif
/**
* Allocate and initialize a shared memory circular buffer.
*
* @internal
*
* rt_scb_init is used to allocate and/or initialize a shared memory circular
* buffer.
*
* @param name is an unsigned long identifier;
*
* @param size is the size of the circular buffer.
*
* @param suprt is the kernel allocation method to be used, it can be:
* - USE_VMALLOC, use vmalloc;
* - USE_GFP_KERNEL, use kmalloc with GFP_KERNEL;
* - USE_GFP_ATOMIC, use kmalloc with GFP_ATOMIC;
* - USE_GFP_DMA, use kmalloc with GFP_DMA.
* - for use in kernel/(multi-threaded)user space only applications the
* user can use "suprt" to pass the address of any memory area (s)he has
* allocated on her/his own. In such a case the actual buffer should be
* greater than the requested size by the amount HDRSIZ at least.
*
* Since @a an unsigned long can be a clumsy identifier, services are provided
* to convert 6 characters identifiers to unsigned long, and vice versa.
*
* @see nam2num() and num2nam().
*
* It must be remarked that only the very first call does a real allocation,
* any following call to allocate with the same name, from anywhere, will just
* increase the usage count and map the circular buffer to the user space, or
* return the related pointer to the already allocated buffer in kernel/user
* space.
* In any case the functions return a pointer to the circular buffer,
* appropriately mapped to the memory space in use. So if one is really sure
* that the named circular buffer has been initted already parameters "size"
* and "suprt" are not used and can be assigned any value.
*
* @returns a valid address on succes, you must use it, 0 on failure.
*
*/
RTAI_SCB_PROTO(void *, rt_scb_init, (unsigned long name, int size, unsigned long suprt))
{
void *scb;
if (suprt > 1000) {
size -= HDRSIZ + 1;
scb = (void *)suprt;
} else {
scb = rt_shm_alloc(name, size + HDRSIZ + 1, suprt);
}
if (scb && !atomic_cmpxchg((atomic_t *)scb, 0, name)) {
((int *)scb)[1] = ((int *)scb)[2] = 0;
((int *)scb)[0] = size + 1;
} else {
while (!((int *)scb)[0]);
}
return scb ? scb + HDRSIZ : 0;
}
/**
* Reset a shared memory circular buffer.
*
* @internal
*
* rt_scb_reset reinitializes a shared memory circular buffer.
*
* @param scb is the pointer returned when the buffer was initted.
*
*/
RTAI_SCB_PROTO(void, rt_scb_reset, (void *scb))
{
LBYTE = FBYTE = 0;
}
/**
* Free a shared memory circular buffer.
*
* @internal
*
* rt_scb_delete is used to release a previously allocated shared memory
* circular buffer.
*
* @param name is the unsigned long identifier used when the buffer was
* allocated;
*
* Analogously to what done by all the named allocation functions the freeing
* calls have just the effect of decrementing a usage count, unmapping any
* user space shared memory being freed, till the last is done, as that is the
* one the really frees any allocated memory.
*
* @returns the size of the succesfully freed buffer, 0 on failure.
*
* No need to call this function if you provided your own memory for the
* circular buffer.
*
*/
RTAI_SCB_PROTO(int, rt_scb_delete, (unsigned long name))
{
return rt_shm_free(name);
}
/**
* Get the number of bytes avaiable in a shared memory circular buffer.
*
* @internal
*
* rt_scb_avbs is used to get the number of bytes avaiable in a shared
* memory circular buffer.
*
* @param scb is the pointer handle returned when the buffer was initted.
*
* @returns the available number of bytes.
*
*/
RTAI_SCB_PROTO (int, rt_scb_avbs, (void *scb))
{
int size = SIZE, fbyte = FBYTE, lbyte = LBYTE;
return (lbyte >= fbyte ? lbyte - fbyte : size + lbyte - fbyte);
}
/**
* Get the number of bytes avaiable in a shared memory circular buffer.
*
* @internal
*
* rt_scb_bytes is used to get the number of bytes avaiable in a shared
* memory circular buffer; legacy alias for rt_scb_avbs.
*
* @param scb is the pointer handle returned when the buffer was initted.
*
* @returns the available number of bytes.
*
*/
RTAI_SCB_PROTO (int, rt_scb_bytes, (void *scb))
{
return rt_scb_avbs(scb);
}
/**
* Get the number of free bytes pace in a shared memory circular buffer.
*
* @internal
*
* rt_scb_frbs is used to get the number of free bytes space avaiable in a
* shared memory circular buffer.
*
* @param scb is the pointer handle returned when the buffer was initted.
*
* @returns the number of free bytes.
*
*/
RTAI_SCB_PROTO (int, rt_scb_frbs, (void *scb))
{
int size = SIZE, fbyte = FBYTE, lbyte = LBYTE;
return (fbyte <= lbyte ? size + fbyte - lbyte : size - lbyte);
}
/**
* @brief Gets (receives) a message, only if the whole message can be passed
* all at once.
*
* rt_scb_get tries to atomically receive the message @e msg of @e
* msg_size bytes from the shared memory circular buffer @e scb.
* It returns immediately and the caller is never blocked.
*
* @return On success, i.e. message got, it returns 0, msg_size on failure.
*
*/
RTAI_SCB_PROTO(int, rt_scb_get, (void *scb, void *msg, int msg_size))
{
int size = SIZE, fbyte = FBYTE, lbyte = LBYTE;
if (msg_size > 0 && ((lbyte -= fbyte) >= 0 ? lbyte : size + lbyte) >= msg_size) {
int tocpy;
if ((tocpy = size - fbyte) > msg_size) {
memcpy(msg, SCB + fbyte, msg_size);
FBYTE = fbyte + msg_size;
} else {
memcpy(msg, SCB + fbyte, tocpy);
memcpy(msg + tocpy, SCB, msg_size -= tocpy);
FBYTE = msg_size;
}
return 0;
}
return msg_size;
}
/**
* @brief eavedrops a message.
*
* rt_scb_evdrp atomically spies the message @e msg of @e
* msg_size bytes from the shared memory circular buffer @e scb.
* It returns immediately and the caller is never blocked. It is like
* rt_scb_get but leaves the message in the shared memory circular buffer.
*
* @return On success, i.e. message got, it returns 0, msg_size on failure.
*
*/
RTAI_SCB_PROTO(int, rt_scb_evdrp, (void *scb, void *msg, int msg_size))
{
int size = SIZE, fbyte = FBYTE, lbyte = LBYTE;
if (msg_size > 0 && ((lbyte -= fbyte) >= 0 ? lbyte : size + lbyte) >= msg_size) {
int tocpy;
if ((tocpy = size - fbyte) > msg_size) {
memcpy(msg, SCB + fbyte, msg_size);
} else {
memcpy(msg, SCB + fbyte, tocpy);
memcpy(msg + tocpy, SCB, msg_size - tocpy);
}
return 0;
}
return msg_size;
}
/**
* @brief Puts (sends) a message, only if the whole message can be passed all
* at once.
*
* rt_scb_put tries to atomically send the message @e msg of @e
* msg_size bytes to the shared memory circular buffer @e scb.
* It returns immediately and the caller is never blocked.
*
* @return On success, i.e. message put, it returns 0, msg_size on failure.
*
*/
RTAI_SCB_PROTO(int, rt_scb_put, (void *scb, void *msg, int msg_size))
{
int size = SIZE, fbyte = FBYTE, lbyte = LBYTE;
if (msg_size > 0 && ((fbyte -= lbyte) <= 0 ? size + fbyte : fbyte) > msg_size) {
int tocpy;
if ((tocpy = size - lbyte) > msg_size) {
memcpy(SCB + lbyte, msg, msg_size);
LBYTE = lbyte + msg_size;
} else {
memcpy(SCB + lbyte, msg, tocpy);
memcpy(SCB, msg + tocpy, msg_size -= tocpy);
LBYTE = msg_size;
}
return 0;
}
return msg_size;
}
RTAI_SCB_PROTO(int, rt_scb_ovrwr, (void *scb, void *msg, int msg_size))
{
int size = SIZE, lbyte = LBYTE;
if (msg_size > 0 && msg_size < size) {
int tocpy;
if ((tocpy = size - lbyte) > msg_size) {
memcpy(SCB + lbyte, msg, msg_size);
LBYTE = lbyte + msg_size;
} else {
memcpy(SCB + lbyte, msg, tocpy);
memcpy(SCB, msg + tocpy, msg_size -= tocpy);
LBYTE = msg_size;
}
return 0;
}
return msg_size;
}
#endif /* _RTAI_SCB_H */
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