ring_buffer.c

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/*
 *   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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: 8495779e4babdb109d907093e391556a1dec8de4 $
 *
 * @brief Simple ring buffers for packet contents
 * @file io/ring_buffer.c
 *
 * @copyright 2016 Alan DeKok (aland@freeradius.org)
 */
RCSID("$Id: 8495779e4babdb109d907093e391556a1dec8de4 $")
 
#include <freeradius-devel/io/ring_buffer.h>
#include <freeradius-devel/util/strerror.h>
#include <freeradius-devel/util/debug.h>
#include <string.h>
 
/*
 *      Ring buffers are allocated in a block.
 */
struct fr_ring_buffer_s {
        uint8_t         *buffer;        //!< actual start of the ring buffer
        size_t          size;           //!< Size of this ring buffer
 
        size_t          data_start;     //!< start of used portion of the buffer
        size_t          data_end;       //!< end of used portion of the buffer
 
        size_t          write_offset;   //!< where writes are done
        size_t          reserved;       //!< amount of reserved data at write_offset
 
        bool            closed;         //!< whether allocations are closed
};
 
/** Create a ring buffer.
 *
 *  The size provided will be rounded up to the next highest power of
 *  2, if it's not already a power of 2.
 *
 *  The ring buffer manages how much room is reserved (i.e. available
 *  to write to), and used.  The application is responsible for
 *  tracking the start of the reservation, *and* it's write offset
 *  within that reservation.
 *
 * @param[in] ctx       a talloc context
 * @param[in] size      of the raw ring buffer array to allocate.
 * @return
 *      - A new ring buffer on success.
 *      - NULL on failure.
 */
fr_ring_buffer_t *fr_ring_buffer_create(TALLOC_CTX *ctx, size_t size)
{
        fr_ring_buffer_t        *rb;
 
        rb = talloc_zero(ctx, fr_ring_buffer_t);
        if (!rb) {
        fail:
                fr_strerror_const("Failed allocating memory.");
                return NULL;
        }
 
        if (size < 1024) size = 1024;
 
        if (size > (1 << 30)) {
                fr_strerror_const("Ring buffer size must be no more than (1 << 30)");
                talloc_free(rb);
                return NULL;
        }
 
        /*
         *      Round up to the nearest power of 2.
         */
        size--;
        size |= size >> 1;
        size |= size >> 2;
        size |= size >> 4;
        size |= size >> 8;
        size |= size >> 16;
        size++;
 
        rb->buffer = talloc_array(rb, uint8_t, size);
        if (!rb->buffer) {
                talloc_free(rb);
                goto fail;
        }
        rb->size = size;
 
        return rb;
}
 
 
/** Reserve room in the ring buffer.
 *
 *  The size does not need to be a power of two.  The application is
 *  responsible for doing cache alignment, if required.
 *
 *  If the reservation fails, the application should create a new ring
 *  buffer, and start reserving data there.
 *
 * @param[in] rb a ring buffer
 * @param[in] size to see if we can reserve
 * @return
 *      - NULL on error.  Which can only be "ring buffer is full".
 *      - pointer to data on success
 */
uint8_t *fr_ring_buffer_reserve(fr_ring_buffer_t *rb, size_t size)
{
        (void) talloc_get_type_abort(rb, fr_ring_buffer_t);
 
        if (rb->closed) {
                fr_strerror_const("Allocation request after ring buffer is closed");
                return NULL;
        }
 
        /*
         *      We're writing to the start of the buffer, and there is
         *      already data in it.  See if the data fits.
         *
         *      |***W....S****E....|
         */
        if (rb->write_offset < rb->data_start) {
                if ((rb->write_offset + size) < rb->data_start) {
                        rb->reserved = size;
                        return rb->buffer + rb->write_offset;
                }
 
                fr_strerror_const("No memory available in ring buffer");
                return NULL;
        }
 
        fr_assert(rb->write_offset == rb->data_end);
 
        /*
         *      Data fits at the end of the ring buffer.
         *
         *      |....S****WE....|
         */
        if ((rb->write_offset + size) <= rb->size) {
                rb->reserved = size;
                return rb->buffer + rb->write_offset;
        }
 
        /*
         *      Data fits at the start of the ring buffer, ensure that
         *      we write it there.  This also catches the case where
         *      data_start==0.
         *
         *      |W....S****E....|
         */
        if (size < rb->data_start) {
                rb->write_offset = 0;
                rb->reserved = size;
                return rb->buffer;
        }
 
        /*
         *      Not enough room for the new data, fail the allocation.
         *
         *      |....S****WE....|
         */
        fr_strerror_const("No memory available in ring buffer");
        return NULL;
}
 
 
/** Mark data as allocated.
 *
 *  The size does not need to be a power of two.  The application is
 *  responsible for doing cache-line alignment, if required.
 *
 *  The application does NOT need to call fr_ring_buffer_reserve() before
 *  calling this function.
 *
 *  If the allocation fails, the application should create a new ring
 *  buffer, and start allocating data there.
 *
 * @param[in] rb a ring buffer
 * @param[in] size to mark as "used" at the tail end of the buffer.
 * @return
 *      - NULL on error.  Which can only be "ring buffer is full".
 *      - pointer to data on success
 */
uint8_t *fr_ring_buffer_alloc(fr_ring_buffer_t *rb, size_t size)
{
        uint8_t *p;
 
        (void) talloc_get_type_abort(rb, fr_ring_buffer_t);
 
        if (rb->closed) {
#ifndef NDEBUG
                fr_strerror_const("Allocation request after ring buffer is closed");
#endif
                return NULL;
        }
 
        /*
         *      Shrink the "reserved" portion of the buffer by the
         *      allocated size.
         */
        if (rb->reserved >= size) {
                rb->reserved -= size;
        } else {
                rb->reserved = 0;
        }
 
        /*
         *      We're writing to the start of the buffer, and there is
         *      already data in it.  See if the data fits.
         *
         *      |***W....S****E....|
         */
        if (rb->write_offset < rb->data_start) {
                if ((rb->write_offset + size) < rb->data_start) {
                        p = rb->buffer + rb->write_offset;
                        rb->write_offset += size;
                        return p;
                }
 
#ifndef NDEBUG
                fr_strerror_const("No memory available in ring buffer");
#endif
                return NULL;
        }
 
        fr_assert(rb->write_offset == rb->data_end);
 
        /*
         *      Data fits at the end of the ring buffer.
         *
         *      |....S****WE....|
         */
        if ((rb->write_offset + size) <= rb->size) {
                p = rb->buffer + rb->write_offset;
 
                rb->write_offset += size;
                rb->data_end = rb->write_offset;
 
                /*
                 *      Don't update write_offset if it's fallen off
                 *      of the end of the buffer.  The data_start may
                 *      be zero, and we don't want to over-write
                 *      that.
                 */
                return p;
        }
 
        /*
         *      Data fits at the start of the ring buffer, ensure that
         *      we write it there.  This also catches the case where
         *      data_start==0.
         *
         *      |W....S****E....|
         */
        if (size < rb->data_start) {
                rb->write_offset = size;
 
                /*
                 *      Don't update data_end.  It points to the tail
                 *      end of the ring buffer.
                 */
                return rb->buffer;
        }
 
        /*
         *      Not enough room for the new data, fail the allocation.
         *
         *      |....S****WE....|
         */
#ifndef NDEBUG
        fr_strerror_const("No memory available in ring buffer");
#endif
        return NULL;
}
 
/** Mark data as free,
 *
 *  The size does not need to be a power of two.  The application is
 *  responsible for doing cache alignment, if required.  The
 *  application is responsible for tracking sizes of packets in the
 *  ring buffer.
 *
 *  If "unused" bytes are more than what's in the buffer, the used
 *  bytes are reset to zero.
 *
 * @param[in] rb a ring buffer
 * @param[in] size_to_free bytes to mark as "unused" in the buffer.
 * @return
 *      - <0 on error.  Which can only be "ring buffer is full".
 *      - 0 on success
 */
int fr_ring_buffer_free(fr_ring_buffer_t *rb, size_t size_to_free)
{
        size_t block_size;
 
        (void) talloc_get_type_abort(rb, fr_ring_buffer_t);
 
        /*
         *      Nothing to free, do nothing.
         */
        if (!size_to_free) return 0;
 
        /*
         *      Freeing data from the middle of the buffer.
         *
         *      |***W....S****E....|
         */
        if (rb->write_offset < rb->data_start) {
                block_size = rb->data_end - rb->data_start;
 
                /*
                 *      |***W....S****E....|, free 3
                 *
                 *      |***W.......S*E....|
                 */
                if (size_to_free < block_size) {
                        rb->data_start += size_to_free;
                        return 0;
                }
 
                /*
                 *      Free all (or more than) the block.
                 */
                rb->data_start = 0;
                rb->data_end = rb->write_offset;
                size_to_free -= block_size;
 
                /*
                 *      Free everything left: empty the buffer
                 *      entirely.  This also handles the case of
                 *      size_to_free==0 and write_offset==0.
                 */
                if (size_to_free == rb->write_offset) {
                        goto empty_buffer;
                }
 
                /*
                 *      The buffer has data but we're not freeing
                 *      any more of it, return.
                 */
                if (!size_to_free) return 0;
        }
 
        fr_assert(rb->write_offset == rb->data_end);
 
        block_size = rb->data_end - rb->data_start;
 
        /*
         *      Freeing too much, return an error.
         */
        if (size_to_free > block_size) {
                fr_strerror_const("Cannot free more memory than exists.");
                return -1;
        }
 
        /*
         *      Free some data from the start.
         */
        if (size_to_free < block_size) {
                rb->data_start += size_to_free;
                return 0;
        }
 
        /*
         *      Free all data in the buffer.
         */
empty_buffer:
        rb->data_start = 0;
        rb->data_end = 0;
        rb->write_offset = 0;
 
        /*
         *      If the ring buffer is closed to all allocations, and
         *      it's now empty, we automatically free it.
         */
        if (rb->closed) talloc_free(rb);
 
        return 0;
}
 
/** Close a ring buffer so that no further allocations can take place.
 *
 *  Once the ring buffer is empty, it will be automatically freed.
 *  It's called "close" and not "delete", because the ring buffer will
 *  still be active until all data has been removed.
 *
 *  If you don't care about the data in the ring buffer, you can just
 *  call talloc_free() on it.
 *
 * @param[in] rb a ring buffer
 * @return
 *      - <0 on error.
 *      - 0 on success
 */
int fr_ring_buffer_close(fr_ring_buffer_t *rb)
{
        (void) talloc_get_type_abort(rb, fr_ring_buffer_t);
 
        rb->closed = true;
        return 0;
}
 
 
/** Get the size of the ring buffer
 *
 * @param[in] rb a ring buffer
 * @return size of the ring buffer.
 *      - <0 on error.
 *      - 0 on success
 */
size_t fr_ring_buffer_size(fr_ring_buffer_t *rb)
{
        (void) talloc_get_type_abort(rb, fr_ring_buffer_t);
 
        return rb->size;
}
 
/** Get the amount of data used in a ring buffer.
 *
 * @param[in] rb a ring buffer
 * @return size of the used data in the ring buffer.
 *      - <0 on error.
 *      - 0 on success
 */
size_t fr_ring_buffer_used(fr_ring_buffer_t *rb)
{
        size_t size;
 
        (void) talloc_get_type_abort(rb, fr_ring_buffer_t);
 
        if (rb->write_offset < rb->data_start) {
                size = rb->write_offset;
        } else {
                fr_assert(rb->write_offset == rb->data_end);
                size = 0;
        }
 
        size += (rb->data_end - rb->data_start);
 
        return size;
}
 
/** Get a pointer to the data at the start of the ring buffer.
 *
 * @param[in] rb a ring buffer
 * @param[out] p_start pointer to data at the start of the ring buffer
 * @param[in] p_size size of the allocated block at the start of the ring buffer.
 * @return size of the used data in the ring buffer.
 *      - <0 on error.
 *      - 0 on success
 */
int fr_ring_buffer_start(fr_ring_buffer_t *rb, uint8_t **p_start, size_t *p_size)
{
        (void) talloc_get_type_abort(rb, fr_ring_buffer_t);
 
        *p_start = rb->buffer + rb->data_start;
 
        if (rb->write_offset < rb->data_start) {
                *p_size = rb->write_offset;
                return 0;
        }
 
        *p_size = (rb->data_end - rb->data_start);
 
        return 0;
}
 
/** Print debug information about the ring buffer
 *
 * @param[in] rb the ring buffer
 * @param[in] fp the FILE where the messages are printed.
 */
void fr_ring_buffer_debug(FILE *fp, fr_ring_buffer_t *rb)
{
        fprintf(fp, "Buffer %p, write_offset %zu, data_start %zu, data_end %zu\n",
                rb->buffer, rb->write_offset, rb->data_start, rb->data_end);
}