Implement ringbuffers.

This avoids a memmove() call every time data in the send buffer is
ACKed. Instead, we now have a memmove() every time the send buffer is
grown, but this happens only a few times at most.

diff --git a/utcp.c b/utcp.c
index ae3b2b6da469a56804ea07c2727c7855e6bffb8d..f94c6e7e1be55ddef85b20efaff91ba143d9a620 100644 (file)
--- a/utcp.c
+++ b/utcp.c
@@ -153,12 +153,40 @@ static int32_t seqdiff(uint32_t a, uint32_t b) {
 }
 
 // Buffer functions
-// TODO: convert to ringbuffers to avoid memmove() operations.
+static bool buffer_wraps(struct buffer *buf) {
+       return buf->size - buf->offset < buf->used;
+}
+
+static bool buffer_resize(struct buffer *buf, uint32_t newsize) {
+       char *newdata = realloc(buf->data, newsize);
+
+       if(!newdata) {
+               return false;
+       }
+
+       buf->data = newdata;
+
+       if(buffer_wraps(buf)) {
+               // Shift the right part of the buffer until it hits the end of the new buffer.
+               // Old situation:
+               // [345......012]
+               // New situation:
+               // [345.........|........012]
+               uint32_t tailsize = buf->size - buf->offset;
+               uint32_t newoffset = newsize - tailsize;
+               memmove(buf + newoffset, buf + buf->offset, tailsize);
+               buf->offset = newoffset;
+       }
+
+       buf->size = newsize;
+       return true;
+}
 
 // Store data into the buffer
 static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data, size_t len) {
        debug("buffer_put_at %lu %lu %lu\n", (unsigned long)buf->used, (unsigned long)offset, (unsigned long)len);
 
+       // Ensure we don't store more than maxsize bytes in total
        size_t required = offset + len;
 
        if(required > buf->maxsize) {
@@ -170,32 +198,41 @@ static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data
                required = buf->maxsize;
        }
 
+       // Check if we need to resize the buffer
        if(required > buf->size) {
                size_t newsize = buf->size;
 
                if(!newsize) {
-                       newsize = required;
-               } else {
-                       do {
-                               newsize *= 2;
-                       } while(newsize < required);
+                       newsize = 4096;
                }
 
+               do {
+                       newsize *= 2;
+               } while(newsize < required);
+
                if(newsize > buf->maxsize) {
                        newsize = buf->maxsize;
                }
 
-               char *newdata = realloc(buf->data, newsize);
-
-               if(!newdata) {
+               if(!buffer_resize(buf, newsize)) {
                        return -1;
                }
+       }
+
+       uint32_t realoffset = buf->offset + offset;
 
-               buf->data = newdata;
-               buf->size = newsize;
+       if(buf->size - buf->offset < offset) {
+               // The offset wrapped
+               realoffset -= buf->size;
        }
 
-       memcpy(buf->data + offset, data, len);
+       if(buf->size - realoffset < len) {
+               // The new chunk of data must be wrapped
+               memcpy(buf->data + realoffset, data, buf->size - realoffset);
+               memcpy(buf->data, (char *)data + buf->size - realoffset, len - (buf->size - realoffset));
+       } else {
+               memcpy(buf->data + realoffset, data, len);
+       }
 
        if(required > buf->used) {
                buf->used = required;
@@ -208,52 +245,72 @@ static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
        return buffer_put_at(buf, buf->used, data, len);
 }
 
-// Get data from the buffer. data can be NULL.
-static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
-       if(len > buf->used) {
-               len = buf->used;
+// Copy data from the buffer without removing it.
+static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
+       // Ensure we don't copy more than is actually stored in the buffer
+       if(offset >= buf->used) {
+               return 0;
        }
 
-       if(data) {
-               memcpy(data, buf->data, len);
+       if(buf->used - offset < len) {
+               len = buf->used - offset;
        }
 
-       if(len < buf->used) {
-               memmove(buf->data, buf->data + len, buf->used - len);
+       uint32_t realoffset = buf->offset + offset;
+
+       if(buf->size - buf->offset < offset) {
+               // The offset wrapped
+               realoffset -= buf->size;
+       }
+
+       if(buf->size - realoffset < len) {
+               // The data is wrapped
+               memcpy(data, buf->data + realoffset, buf->size - realoffset);
+               memcpy((char *)data + buf->size - realoffset, buf->data, len - (buf->size - realoffset));
+       } else {
+               memcpy(data, buf->data + realoffset, len);
        }
 
-       buf->used -= len;
        return len;
 }
 
-// Copy data from the buffer without removing it.
-static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
-       if(offset >= buf->used) {
-               return 0;
-       }
+// Get data from the buffer.
+static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
+       len = buffer_copy(buf, data, 0, len);
 
-       if(offset + len > buf->used) {
-               len = buf->used - offset;
+       if(buf->size - buf->offset < len) {
+               buf->offset -= buf->size;
        }
 
-       memcpy(data, buf->data + offset, len);
+       buf->offset += len;
+       buf->used -= len;
        return len;
 }
 
-static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
-       memset(buf, 0, sizeof(*buf));
+// Discard data from the buffer.
+static ssize_t buffer_discard(struct buffer *buf, size_t len) {
+       if(buf->used < len) {
+               len = buf->used;
+       }
 
-       if(len) {
-               buf->data = malloc(len);
+       if(buf->size - buf->offset < len) {
+               buf->offset -= buf->size;
+       }
 
-               if(!buf->data) {
-                       return false;
-               }
+       buf->offset += len;
+       buf->used -= len;
+
+       return len;
+}
+
+static bool buffer_set_size(struct buffer *buf, uint32_t minsize, uint32_t maxsize) {
+       if(maxsize < minsize) {
+               maxsize = minsize;
        }
 
-       buf->size = len;
-       buf->maxsize = maxlen;
-       return true;
+       buf->maxsize = maxsize;
+
+       return buf->size >= minsize || buffer_resize(buf, minsize);
 }
 
 static void buffer_exit(struct buffer *buf) {
@@ -360,12 +417,12 @@ static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t s
                return NULL;
        }
 
-       if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
+       if(!buffer_set_size(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
                free(c);
                return NULL;
        }
 
-       if(!buffer_init(&c->rcvbuf, DEFAULT_RCVBUFSIZE, DEFAULT_MAXRCVBUFSIZE)) {
+       if(!buffer_set_size(&c->rcvbuf, DEFAULT_RCVBUFSIZE, DEFAULT_MAXRCVBUFSIZE)) {
                buffer_exit(&c->sndbuf);
                free(c);
                return NULL;
@@ -1308,7 +1365,7 @@ synack:
 #endif
 
                if(data_acked) {
-                       buffer_get(&c->sndbuf, NULL, data_acked);
+                       buffer_discard(&c->sndbuf, data_acked);
                }
 
                // Also advance snd.nxt if possible
@@ -1886,18 +1943,21 @@ uint16_t utcp_get_mtu(struct utcp *utcp) {
 }
 
 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
-       if (!utcp) {
+       if(!utcp) {
                return;
        }
 
-       if (mtu <= sizeof(struct hdr)) {
+       if(mtu <= sizeof(struct hdr)) {
                return;
        }
 
-       if (mtu > utcp->mtu) {
-               char *new = realloc(utcp->pkt, mtu);
-               if (!new)
+       if(mtu > utcp->mtu) {
+               char *new = realloc(utcp->pkt, mtu + sizeof(struct hdr));
+
+               if(!new) {
                        return;
+               }
+
                utcp->pkt = new;
        }
 

diff --git a/utcp_priv.h b/utcp_priv.h
index 1f72fb482c9c7b5140ab730936c738561ad88ab6..9331cd2d617653aaaa40f5353a06b02d75245e5a 100644 (file)
--- a/utcp_priv.h
+++ b/utcp_priv.h
@@ -89,6 +89,7 @@ static const char *strstate[] __attribute__((unused)) = {
 
 struct buffer {
        char *data;
+       uint32_t offset;
        uint32_t used;
        uint32_t size;
        uint32_t maxsize;