src/svm/svm_fifo.h

/*
 * Copyright (c) 2016-2019 Cisco and/or its affiliates.
 * Copyright (c) 2019 Arm Limited
 * Copyright (c) 2010-2017 Intel Corporation and/or its affiliates.
 * Copyright (c) 2007-2009 Kip Macy kmacy@freebsd.org
 * Inspired from DPDK rte_ring.h (SPSC only) (derived from freebsd bufring.h).
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#ifndef __included_ssvm_fifo_h__
#define __included_ssvm_fifo_h__

#include <vppinfra/clib.h>
#include <vppinfra/vec.h>
#include <vppinfra/pool.h>
#include <vppinfra/format.h>
#include <vppinfra/rbtree.h>

/** Out-of-order segment */
typedef struct
{
  u32 next;	/**< Next linked-list element pool index */
  u32 prev;	/**< Previous linked-list element pool index */
  u32 start;	/**< Start of segment, normalized*/
  u32 length;	/**< Length of segment */
} ooo_segment_t;

#define SVM_FIFO_TRACE 			(0)
#define OOO_SEGMENT_INVALID_INDEX 	((u32)~0)
#define SVM_FIFO_INVALID_SESSION_INDEX 	((u32)~0)
#define SVM_FIFO_INVALID_INDEX		((u32)~0)
#define SVM_FIFO_MAX_EVT_SUBSCRIBERS	7

typedef enum svm_fifo_tx_ntf_
{
  SVM_FIFO_NO_TX_NOTIF = 0,
  SVM_FIFO_WANT_TX_NOTIF = 1,
  SVM_FIFO_WANT_TX_NOTIF_IF_FULL = 2,
} svm_fifo_tx_ntf_t;

typedef struct
{
  u32 offset;
  u32 len;
  u32 action;
} svm_fifo_trace_elem_t;

typedef struct svm_fifo_chunk_
{
  u32 start_byte;		/**< chunk start byte */
  u32 length;			/**< length of chunk in bytes */
  struct svm_fifo_chunk_ *next;	/**< pointer to next chunk in linked-lists */
  u8 data[0];			/**< start of chunk data */
} svm_fifo_chunk_t;

typedef enum svm_fifo_flag_
{
  SVM_FIFO_F_MULTI_CHUNK = 1 << 0,
  SVM_FIFO_F_GROW = 1 << 1,
  SVM_FIFO_F_SHRINK = 1 << 2,
  SVM_FIFO_F_COLLECT_CHUNKS = 1 << 3,
  SVM_FIFO_F_LL_TRACKED = 1 << 4,
} svm_fifo_flag_t;

typedef struct _svm_fifo
{
  CLIB_CACHE_LINE_ALIGN_MARK (shared_first);
  u32 size;			/**< size of the fifo in bytes */
  u32 nitems;			/**< usable size (size-1) */
  u8 flags;			/**< fifo flags */
  svm_fifo_chunk_t *start_chunk;/**< first chunk in fifo chunk list */
  svm_fifo_chunk_t *end_chunk;	/**< end chunk in fifo chunk list */
  svm_fifo_chunk_t *new_chunks;	/**< chunks yet to be added to list */
  rb_tree_t chunk_lookup;

    CLIB_CACHE_LINE_ALIGN_MARK (shared_second);
  volatile u32 has_event;	/**< non-zero if deq event exists */
  u32 master_session_index;	/**< session layer session index */
  u32 client_session_index;	/**< app session index */
  u8 master_thread_index;	/**< session layer thread index */
  u8 client_thread_index;	/**< app worker index */
  i8 refcnt;			/**< reference count  */
  u32 segment_manager;		/**< session layer segment manager index */
  u32 segment_index;		/**< segment index in segment manager */
  struct _svm_fifo *next;	/**< next in freelist/active chain */
  struct _svm_fifo *prev;	/**< prev in active chain */
  u32 size_decrement;		/**< bytes to remove from fifo */

    CLIB_CACHE_LINE_ALIGN_MARK (consumer);
  u32 head;			/**< fifo head position/byte */
  svm_fifo_chunk_t *head_chunk;	/**< tracks chunk where head lands */
  svm_fifo_chunk_t *ooo_deq;	/**< last chunk used for ooo dequeue */
  volatile u32 want_tx_ntf;	/**< producer wants nudge */
  volatile u32 has_tx_ntf;

    CLIB_CACHE_LINE_ALIGN_MARK (producer);
  u32 tail;			/**< fifo tail position/byte */
  u32 ooos_list_head;		/**< Head of out-of-order linked-list */
  svm_fifo_chunk_t *tail_chunk;	/**< tracks chunk where tail lands */
  svm_fifo_chunk_t *ooo_enq;	/**< last chunk used for ooo enqueue */
  ooo_segment_t *ooo_segments;	/**< Pool of ooo segments */
  u32 ooos_newest;		/**< Last segment to have been updated */
  volatile u8 n_subscribers;	/**< Number of subscribers for io events */
  u8 subscribers[SVM_FIFO_MAX_EVT_SUBSCRIBERS];

#if SVM_FIFO_TRACE
  svm_fifo_trace_elem_t *trace;
#endif

} svm_fifo_t;

typedef enum
{
  SVM_FIFO_EFULL = -2,
  SVM_FIFO_EEMPTY = -3,
} svm_fifo_err_t;

typedef struct svm_fifo_seg_
{
  u8 *data;
  u32 len;
} svm_fifo_seg_t;

#if SVM_FIFO_TRACE
#define svm_fifo_trace_add(_f, _s, _l, _t)		\
{							\
  svm_fifo_trace_elem_t *trace_elt;			\
  vec_add2(_f->trace, trace_elt, 1);			\
  trace_elt->offset = _s;				\
  trace_elt->len = _l;					\
  trace_elt->action = _t;				\
}
#else
#define svm_fifo_trace_add(_f, _s, _l, _t)
#endif

u8 *svm_fifo_dump_trace (u8 * s, svm_fifo_t * f);
u8 *svm_fifo_replay (u8 * s, svm_fifo_t * f, u8 no_read, u8 verbose);

/**
 * Load head and tail optimized for consumer
 *
 * Internal function.
 */
static inline void
f_load_head_tail_cons (svm_fifo_t * f, u32 * head, u32 * tail)
{
  /* load-relaxed: consumer owned index */
  *head = f->head;
  /* load-acq: consumer foreign index (paired with store-rel in producer) */
  *tail = clib_atomic_load_acq_n (&f->tail);
}

/** Load head and tail optimized for producer
 *
 * Internal function
 */
static inline void
f_load_head_tail_prod (svm_fifo_t * f, u32 * head, u32 * tail)
{
  /* load relaxed: producer owned index */
  *tail = f->tail;
  /* load-acq: producer foreign index (paired with store-rel in consumer) */
  *head = clib_atomic_load_acq_n (&f->head);
}

/**
 * Load head and tail independent of producer/consumer role
 *
 * Internal function.
 */
static inline void
f_load_head_tail_all_acq (svm_fifo_t * f, u32 * head, u32 * tail)
{
  /* load-acq : consumer foreign index (paired with store-rel) */
  *tail = clib_atomic_load_acq_n (&f->tail);
  /* load-acq : producer foriegn index (paired with store-rel) */
  *head = clib_atomic_load_acq_n (&f->head);
}

/**
 * Distance to a from b, i.e., a - b in the fifo
 *
 * Internal function.
 */
static inline u32
f_distance_to (svm_fifo_t * f, u32 a, u32 b)
{
  return ((f->size + a - b) % f->size);
}

/**
 * Distance from a to b, i.e., b - a in the fifo
 *
 * Internal function.
 */
static inline u32
f_distance_from (svm_fifo_t * f, u32 a, u32 b)
{
  return ((f->size + b - a) % f->size);
}

/**
 * Fifo current size, i.e., number of bytes enqueued
 *
 * Internal function.
 */
static inline u32
f_cursize (svm_fifo_t * f, u32 head, u32 tail)
{
  return (head <= tail ? tail - head : f->size + tail - head);
}

/**
 * Fifo free bytes, i.e., number of free bytes
 *
 * Internal function
 */
static inline u32
f_free_count (svm_fifo_t * f, u32 head, u32 tail)
{
  return (f->nitems - f_cursize (f, head, tail));
}

/**
 * Try to shrink fifo size.
 *
 * Internal function.
 */
void svm_fifo_try_shrink (svm_fifo_t * f, u32 head, u32 tail);

/**
 * Create fifo of requested size
 *
 * Allocates fifo on current heap.
 *
 * @param size		data size in bytes for fifo to be allocated. Will be
 * 			rounded to the next highest power-of-two value.
 * @return 		pointer to new fifo
 */
svm_fifo_t *svm_fifo_create (u32 size);
/**
 * Initialize fifo
 *
 * @param size		size for fifo
 */
void svm_fifo_init (svm_fifo_t * f, u32 size);
/**
 * Allocate a fifo chunk on heap
 *
 * If the chunk is allocated on a fifo segment, this should be called
 * with the segment's heap pushed.
 *
 * @param size	chunk size in bytes. Will be rounded to the next highest
 * 		power-of-two
 * @return	new chunk or 0 if alloc failed
 */
svm_fifo_chunk_t *svm_fifo_chunk_alloc (u32 size);
/**
 * Grow fifo size by adding chunk to chunk list
 *
 * If fifos are allocated on a segment, this should be called with
 * the segment's heap pushed.
 *
 * @param f	fifo to be extended
 * @param c 	chunk or linked list of chunks to be added
 */
void svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c);
/**
 * Request to reduce fifo size by amount of bytes
 *
 * Because the producer might be enqueuing data when this is called, the
 * actual size update is only applied when producer tries to enqueue new
 * data, unless @param try_shrink is set.
 *
 * @param f		fifo
 * @param len		number of bytes to remove from fifo. The actual number
 * 			of bytes to be removed will be less or equal to this
 * 			value.
 * @param try_shrink	flg to indicate if it's safe to try to shrink fifo
 * 			size. It should be set only if this is called by the
 * 			producer of if the producer is not using the fifo
 * @return		actual length fifo size will be reduced by
 */
int svm_fifo_reduce_size (svm_fifo_t * f, u32 len, u8 try_shrink);
/**
 * Removes chunks that are after fifo end byte
 *
 * Needs to be called with segment heap pushed.
 *
 * @param f fifo
 */
svm_fifo_chunk_t *svm_fifo_collect_chunks (svm_fifo_t * f);
/**
 * Free fifo and associated state
 *
 * @param f	fifo
 */
void svm_fifo_free (svm_fifo_t * f);
/**
 * Cleanup fifo chunk lookup rb tree
 *
 * The rb tree is allocated in segment heap so this should be called
 * with it pushed.
 *
 * @param f 	fifo to cleanup
 */
void svm_fifo_free_chunk_lookup (svm_fifo_t * f);
/**
 * Cleanup fifo ooo data
 *
 * The ooo data is allocated in producer process memory. The fifo
 * segment heap should not be pushed.
 *
 * @param f	fifo to cleanup
 */
void svm_fifo_free_ooo_data (svm_fifo_t * f);
/**
 * Init fifo head and tail
 *
 * @param f	fifo
 * @param head	head value that will be matched to a chunk
 * @param tail	tail value that will be matched to a chunk
 */
void svm_fifo_init_pointers (svm_fifo_t * f, u32 head, u32 tail);
/**
 * Clone fifo
 *
 * Clones single/default chunk fifo. It does not work for fifos with
 * multiple chunks.
 */
void svm_fifo_clone (svm_fifo_t * df, svm_fifo_t * sf);
/**
 * Enqueue data to fifo
 *
 * Data is enqueued and tail pointer is updated atomically. If the new data
 * enqueued partly overlaps or "touches" an out-of-order segment, said segment
 * is "consumed" and the number of bytes returned is appropriately updated.
 *
 * @param f	fifo
 * @param len	length of data to copy
 * @param src	buffer from where to copy the data
 * @return	number of contiguous bytes that can be consumed or error
 */
int svm_fifo_enqueue (svm_fifo_t * f, u32 len, const u8 * src);
/**
 * Enqueue data to fifo with offset
 *
 * Data is enqueued without updating tail pointer. Instead, an out-of-order
 * list of segments is generated and maintained. Fifo takes care of coalescing
 * contiguous or overlapping segments.
 *
 * @param f		fifo
 * @param offset	offset at which to copy the data
 * @param len		len of data to copy
 * @param src		buffer from where to copy the data
 * @return		0 if enqueue was successful, error otherwise
 */
int svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len,
				  u8 * src);

/**
 * Advance tail pointer
 *
 * Useful for moving tail pointer after external enqueue.
 *
 * @param f		fifo
 * @param len		number of bytes to add to tail
 */
void svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 len);
/**
 * Overwrite fifo head with new data
 *
 * This should be typically used by dgram transport protocols that need
 * to update the dgram header after dequeueing a chunk of data. It assumes
 * that the dgram header is at most spread over two chunks.
 *
 * @param f		fifo
 * @param src		src of new data
 * @param len		length of new data
 */
void svm_fifo_overwrite_head (svm_fifo_t * f, u8 * src, u32 len);
/**
 * Dequeue data from fifo
 *
 * Data is dequeued to consumer provided buffer and head is atomically
 * updated.
 *
 * @param f		fifo
 * @param len		length of data to dequeue
 * @param dst		buffer to where to dequeue the data
 * @return		number of bytes dequeued or error
 */
int svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst);
/**
 * Peek data from fifo
 *
 * Data is copied from requested offset into provided dst buffer. Head is
 * not updated.
 *
 * @param f		fifo
 * @param offset	offset from which to copy the data
 * @param len		length of data to copy
 * @param dst		buffer to where to dequeue the data
 * @return		number of bytes peeked
 */
int svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 len, u8 * dst);
/**
 * Dequeue and drop bytes from fifo
 *
 * Advances fifo head by requested amount of bytes.
 *
 * @param f		fifo
 * @param len		number of bytes to drop
 * @return		number of bytes dropped
 */
int svm_fifo_dequeue_drop (svm_fifo_t * f, u32 len);
/**
 * Dequeue and drop all bytes from fifo
 *
 * Advances head to tail position.
 *
 * @param f		fifo
 */
void svm_fifo_dequeue_drop_all (svm_fifo_t * f);
int svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs);
void svm_fifo_segments_free (svm_fifo_t * f, svm_fifo_seg_t * fs);
/**
 * Add io events subscriber to list
 *
 * @param f	fifo
 * @param sub	subscriber opaque index (typically app worker index)
 */
void svm_fifo_add_subscriber (svm_fifo_t * f, u8 sub);
/**
 * Remove io events subscriber form list
 *
 * @param f	fifo
 * @param sub	subscriber index to be removed
 */
void svm_fifo_del_subscriber (svm_fifo_t * f, u8 subscriber);
/**
 * Number of out-of-order segments for fifo
 *
 * @param f	fifo
 * @return	number of out of order segments
 */
u32 svm_fifo_n_ooo_segments (svm_fifo_t * f);
/*
 * First out-of-order segment for fifo
 *
 * @param f	fifo
 * @return	first out-of-order segment for fifo
 */
ooo_segment_t *svm_fifo_first_ooo_segment (svm_fifo_t * f);
format_function_t format_svm_fifo;

/**
 * Fifo max bytes to dequeue optimized for consumer
 *
 * @param f	fifo
 * @return	max number of bytes that can be dequeued
 */
static inline u32
svm_fifo_max_dequeue_cons (svm_fifo_t * f)
{
  u32 tail, head;
  f_load_head_tail_cons (f, &head, &tail);
  return f_cursize (f, head, tail);
}

/**
 * Fifo max bytes to dequeue optimized for producer
 *
 * @param f	fifo
 * @return	max number of bytes that can be dequeued
 */
static inline u32
svm_fifo_max_dequeue_prod (svm_fifo_t * f)
{
  u32 tail, head;
  f_load_head_tail_prod (f, &head, &tail);
  return f_cursize (f, head, tail);
}

/**
 * Fifo max bytes to dequeue
 *
 * Note: use producer or consumer specific functions for performance:
 * @ref svm_fifo_max_dequeue_cons (svm_fifo_t *f)
 * @ref svm_fifo_max_dequeue_prod (svm_fifo_t *f)
 */
static inline u32
svm_fifo_max_dequeue (svm_fifo_t * f)
{
  u32 tail, head;
  f_load_head_tail_all_acq (f, &head, &tail);
  return f_cursize (f, head, tail);
}

/**
 * Check if fifo is full optimized for producer
 *
 * @param f	fifo
 * @return	1 if fifo is full 0 otherwise
 */
static inline int
svm_fifo_is_full_prod (svm_fifo_t * f)
{
  return (svm_fifo_max_dequeue_prod (f) == f->nitems);
}

/* Check if fifo is full.
 *
 * Note: use producer or consumer specific functions for performance.
 * @ref svm_fifo_is_full_prod (svm_fifo_t * f)
 * add cons version if needed
 */
static inline int
svm_fifo_is_full (svm_fifo_t * f)
{
  return (svm_fifo_max_dequeue (f) == f->nitems);
}

/**
 * Check if fifo is empty optimized for consumer
 *
 * @param f 	fifo
 * @return	1 if fifo is empty 0 otherwise
 */
static inline int
svm_fifo_is_empty_cons (svm_fifo_t * f)
{
  return (svm_fifo_max_dequeue_cons (f) == 0);
}

/**
 * Check if fifo is empty optimized for producer
 *
 * @param f	fifo
 * @return	1 if fifo is empty 0 otherwise
 */
static inline int
svm_fifo_is_empty_prod (svm_fifo_t * f)
{
  return (svm_fifo_max_dequeue_prod (f) == 0);
}

/**
 * Check if fifo is empty
 *
 * Note: use producer or consumer specific functions for perfomance.
 * @ref svm_fifo_is_empty_cons (svm_fifo_t * f)
 * @ref svm_fifo_is_empty_prod (svm_fifo_t * f)
 */
static inline int
svm_fifo_is_empty (svm_fifo_t * f)
{
  return (svm_fifo_max_dequeue (f) == 0);
}

/**
 * Check if fifo is wrapped
 *
 * @param f	fifo
 * @return 	1 if 'normalized' head is ahead of tail
 */
static inline u8
svm_fifo_is_wrapped (svm_fifo_t * f)
{
  u32 head, tail;
  f_load_head_tail_all_acq (f, &head, &tail);
  return head > tail;
}

/**
 * Maximum number of bytes that can be enqueued into fifo
 *
 * Optimized for producer
 *
 * @param f	fifo
 * @return	max number of bytes that can be enqueued into fifo
 */
static inline u32
svm_fifo_max_enqueue_prod (svm_fifo_t * f)
{
  u32 head, tail;
  f_load_head_tail_prod (f, &head, &tail);
  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SHRINK))
    svm_fifo_try_shrink (f, head, tail);
  return f_free_count (f, head, tail);
}

/* Maximum number of bytes that can be enqueued into fifo
 *
 * Note: use producer or consumer specific functions for performance.
 * @ref svm_fifo_max_enqueue_prod (svm_fifo_t *f)
 * add consumer specific version if needed.
 */
static inline u32
svm_fifo_max_enqueue (svm_fifo_t * f)
{
  u32 head, tail;
  f_load_head_tail_all_acq (f, &head, &tail);
  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SHRINK))
    svm_fifo_try_shrink (f, head, tail);
  return f_free_count (f, head, tail);
}

/**
 * Max contiguous chunk of data that can be read
 */
static inline u32
svm_fifo_max_read_chunk (svm_fifo_t * f)
{
  u32 head, tail;
  f_load_head_tail_cons (f, &head, &tail);
  return tail >= head ? (tail - head) : (f->size - head);
}

/**
 * Max contiguous chunk of data that can be written
 */
static inline u32
svm_fifo_max_write_chunk (svm_fifo_t * f)
{
  u32 head, tail;
  f_load_head_tail_prod (f, &head, &tail);
  return tail > head ? f->size - tail : f_free_count (f, head, tail);
}

static inline u8 *
svm_fifo_head (svm_fifo_t * f)
{
  /* load-relaxed: consumer owned index */
  return (f->head_chunk->data + (f->head - f->head_chunk->start_byte));
}

static inline u8 *
svm_fifo_tail (svm_fifo_t * f)
{
  /* load-relaxed: producer owned index */
  return (f->tail_chunk->data + (f->tail - f->tail_chunk->start_byte));
}

static inline u8
svm_fifo_n_subscribers (svm_fifo_t * f)
{
  return f->n_subscribers;
}

/**
 * Check if fifo has out-of-order data
 *
 * @param f	fifo
 * @return	1 if fifo has ooo data, 0 otherwise
 */
static inline u8
svm_fifo_has_ooo_data (svm_fifo_t * f)
{
  return f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX;
}

static inline ooo_segment_t *
svm_fifo_newest_ooo_segment (svm_fifo_t * f)
{
  if (f->ooos_newest == OOO_SEGMENT_INVALID_INDEX)
    return 0;
  return pool_elt_at_index (f->ooo_segments, f->ooos_newest);
}

static inline void
svm_fifo_newest_ooo_segment_reset (svm_fifo_t * f)
{
  f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
}

static inline u32
ooo_segment_offset_prod (svm_fifo_t * f, ooo_segment_t * s)
{
  u32 tail;
  /* load-relaxed: producer owned index */
  tail = f->tail;

  return f_distance_to (f, s->start, tail);
}

static inline u32
ooo_segment_length (svm_fifo_t * f, ooo_segment_t * s)
{
  return s->length;
}

/**
 * Check if fifo has io event
 *
 * @param f	fifo
 * @return	1 if fifo has event, 0 otherwise
 */
static inline int
svm_fifo_has_event (svm_fifo_t * f)
{
  return f->has_event;
}

/**
 * Set fifo event flag.
 *
 * Forces release semantics.
 *
 * @param f	fifo
 * @return 	1 if flag was not set, 0 otherwise
 */
always_inline u8
svm_fifo_set_event (svm_fifo_t * f)
{
  return !clib_atomic_swap_rel_n (&f->has_event, 1);
}

/**
 * Unset fifo event flag.
 *
 * Forces acquire semantics
 *
 * @param f	fifo
 */
always_inline void
svm_fifo_unset_event (svm_fifo_t * f)
{
  clib_atomic_swap_acq_n (&f->has_event, 0);
}

/**
 * Set specific want tx notification flag
 *
 * For list of flags see @ref svm_fifo_tx_ntf_t
 *
 * @param f		fifo
 * @param ntf_type	type of notification requested
 */
static inline void
svm_fifo_add_want_tx_ntf (svm_fifo_t * f, u8 ntf_type)
{
  f->want_tx_ntf |= ntf_type;
}

/**
 * Clear specific want tx notification flag
 *
 * For list of flags see @ref svm_fifo_tx_ntf_t
 *
 * @param f 		fifo
 * @param ntf_type	type of notification to be cleared
 */
static inline void
svm_fifo_del_want_tx_ntf (svm_fifo_t * f, u8 ntf_type)
{
  f->want_tx_ntf &= ~ntf_type;
}

/**
 * Clear the want tx notification flag and set has tx notification
 *
 * Should be used after enqueuing a tx event. This clears the
 * SVM_FIFO_WANT_TX_NOTIF flag but it does not clear
 * SVM_FIFO_WANT_TX_NOTIF_IF_FULL. If the latter was set, has_tx_ntf is
 * set to avoid enqueueing tx events for for all dequeue operations until
 * it is manually cleared.
 *
 * @param f	fifo
 */
static inline void
svm_fifo_clear_tx_ntf (svm_fifo_t * f)
{
  /* Set the flag if want_tx_notif_if_full was the only ntf requested */
  f->has_tx_ntf = f->want_tx_ntf == SVM_FIFO_WANT_TX_NOTIF_IF_FULL;
  svm_fifo_del_want_tx_ntf (f, SVM_FIFO_WANT_TX_NOTIF);
}

/**
 * Clear has tx notification flag
 *
 * The fifo generates only one event per SVM_FIFO_WANT_TX_NOTIF_IF_FULL
 * request and sets has_tx_ntf. To received new events the flag must be
 * cleared using this function.
 *
 * @param f	fifo
 */
static inline void
svm_fifo_reset_tx_ntf (svm_fifo_t * f)
{
  f->has_tx_ntf = 0;
}

/**
 * Check if fifo needs tx notification
 *
 * Determines based on tx notification request flags and state of the fifo if
 * a tx io event should be generated.
 *
 * @param f		fifo
 * @param n_last_deq	number of bytes last dequeued
 * @return		1 if tx io event should be generated, 0 otherwise
 */
static inline u8
svm_fifo_needs_tx_ntf (svm_fifo_t * f, u32 n_last_deq)
{
  u8 want_ntf = f->want_tx_ntf;

  if (PREDICT_TRUE (want_ntf == SVM_FIFO_NO_TX_NOTIF))
    return 0;
  else if (want_ntf & SVM_FIFO_WANT_TX_NOTIF)
    return 1;
  else if (want_ntf & SVM_FIFO_WANT_TX_NOTIF_IF_FULL)
    {
      u32 max_deq = svm_fifo_max_dequeue_cons (f);
      u32 nitems = f->nitems;
      if (!f->has_tx_ntf && max_deq < nitems
	  && max_deq + n_last_deq >= nitems)
	return 1;

      return 0;
    }
  return 0;
}

#endif /* __included_ssvm_fifo_h__ */

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