kern/mbuf: new module

1 files changed, 261 insertions, 0 deletions

diff --git a/kern/mbuf.c b/kern/mbuf.c
new file mode 100644
index 00000000..5ac06955
--- /dev/null
+++ b/kern/mbuf.c
@@ -0,0 +1,261 @@
+/*
+ * Copyright (c) 2018-2019 Richard Braun.
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ *
+ * Upstream site with license notes :
+ * http://git.sceen.net/rbraun/librbraun.git/
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <kern/macros.h>
+#include <kern/mbuf.h>
+
+/*
+ * Message header.
+ *
+ * The size denotes the size of the data, without the header.
+ */
+union mbuf_hdr {
+    uint8_t size1;
+    uint16_t size2;
+    uint32_t size4;
+#ifdef __LP64__
+    uint64_t size8;
+#endif /* __LP64__ */
+};
+
+static size_t
+mbuf_compute_hdr_size(unsigned int order)
+{
+    return order / CHAR_BIT;
+}
+
+static void *
+mbuf_hdr_get_msg_size_addr(union mbuf_hdr *hdr, unsigned int order)
+{
+    switch (order) {
+    case 8:
+        return &hdr->size1;
+    case 16:
+        return &hdr->size2;
+    default:
+#ifdef __LP64__
+        return &hdr->size8;
+    case 32:
+#endif /* __LP64__ */
+        return &hdr->size4;
+    }
+}
+
+static size_t
+mbuf_hdr_get_msg_size(const union mbuf_hdr *hdr, unsigned int order)
+{
+    switch (order) {
+    case 8:
+        return hdr->size1;
+    case 16:
+        return hdr->size2;
+    default:
+#ifdef __LP64__
+        return hdr->size8;
+    case 32:
+#endif /* __LP64__ */
+        return hdr->size4;
+    }
+}
+
+static void
+mbuf_hdr_init(union mbuf_hdr *hdr, unsigned int order, size_t size)
+{
+    switch (order) {
+    case 8:
+        assert(size <= UINT8_MAX);
+        hdr->size1 = size;
+        break;
+    case 16:
+        assert(size <= UINT16_MAX);
+        hdr->size2 = size;
+        break;
+    default:
+#ifdef __LP64__
+        hdr->size8 = size;
+        break;
+    case 32:
+        assert(size <= UINT32_MAX);
+#endif /* __LP64__ */
+        hdr->size4 = size;
+    }
+}
+
+static size_t
+mbuf_hdr_get_total_msg_size(const union mbuf_hdr *hdr, unsigned int order)
+{
+    return mbuf_compute_hdr_size(order) + mbuf_hdr_get_msg_size(hdr, order);
+}
+
+static unsigned int
+mbuf_compute_order(size_t max_msg_size)
+{
+    unsigned int order;
+
+    assert(max_msg_size != 0);
+    order = (sizeof(max_msg_size) * CHAR_BIT) - __builtin_clzl(max_msg_size);
+    return P2ROUND(order, CHAR_BIT);
+}
+
+void
+mbuf_init(struct mbuf *mbuf, void *buf, size_t capacity, size_t max_msg_size)
+{
+    cbuf_init(&mbuf->cbuf, buf, capacity);
+    mbuf->max_msg_size = max_msg_size;
+    mbuf->order = mbuf_compute_order(max_msg_size);
+}
+
+void
+mbuf_clear(struct mbuf *mbuf)
+{
+    return cbuf_clear(&mbuf->cbuf);
+}
+
+static void
+mbuf_clear_old_msgs(struct mbuf *mbuf, size_t total_size)
+{
+    union mbuf_hdr hdr;
+    void *msg_size_addr;
+    size_t hdr_size;
+
+    hdr_size = mbuf_compute_hdr_size(mbuf->order);
+    msg_size_addr = mbuf_hdr_get_msg_size_addr(&hdr, mbuf->order);
+
+    do {
+        size_t msg_size, size;
+        int error;
+
+        size = hdr_size;
+        error = cbuf_pop(&mbuf->cbuf, msg_size_addr, &size);
+        assert(!error);
+
+        if (size == 0) {
+            break;
+        }
+
+        msg_size = mbuf_hdr_get_msg_size(&hdr, mbuf->order);
+        size = msg_size;
+        error = cbuf_pop(&mbuf->cbuf, NULL, &size);
+        assert(!error && (size == msg_size));
+    } while (cbuf_avail_size(&mbuf->cbuf) < total_size);
+}
+
+int
+mbuf_push(struct mbuf *mbuf, const void *buf, size_t size, bool erase)
+{
+    union mbuf_hdr hdr;
+    void *msg_size_addr;
+    size_t hdr_size, total_size;
+    int error;
+
+    if (size > mbuf->max_msg_size) {
+        return EINVAL;
+    }
+
+    mbuf_hdr_init(&hdr, mbuf->order, size);
+
+    total_size = mbuf_hdr_get_total_msg_size(&hdr, mbuf->order);
+
+    if (total_size > cbuf_avail_size(&mbuf->cbuf)) {
+        if (!erase || (total_size > cbuf_capacity(&mbuf->cbuf))) {
+            return EMSGSIZE;
+        }
+
+        mbuf_clear_old_msgs(mbuf, total_size);
+    }
+
+    hdr_size = mbuf_compute_hdr_size(mbuf->order);
+    msg_size_addr = mbuf_hdr_get_msg_size_addr(&hdr, mbuf->order);
+
+    error = cbuf_push(&mbuf->cbuf, msg_size_addr, hdr_size, erase);
+    assert(!error);
+    error = cbuf_push(&mbuf->cbuf, buf, size, erase);
+    assert(!error);
+
+    return 0;
+}
+
+int
+mbuf_pop(struct mbuf *mbuf, void *buf, size_t *sizep)
+{
+    size_t start;
+    int error;
+
+    start = cbuf_start(&mbuf->cbuf);
+    error = mbuf_read(mbuf, &start, buf, sizep);
+
+    if (!error) {
+        cbuf_set_start(&mbuf->cbuf, start);
+    }
+
+    return error;
+}
+
+int
+mbuf_read(const struct mbuf *mbuf, size_t *indexp, void *buf, size_t *sizep)
+{
+    union mbuf_hdr hdr;
+    void *msg_size_addr;
+    size_t hdr_size, msg_size, size;
+    int error;
+
+    hdr_size = mbuf_compute_hdr_size(mbuf->order);
+    msg_size_addr = mbuf_hdr_get_msg_size_addr(&hdr, mbuf->order);
+
+    size = hdr_size;
+    error = cbuf_read(&mbuf->cbuf, *indexp, msg_size_addr, &size);
+
+    if (error) {
+        return error;
+    } else if (size == 0) {
+        return EAGAIN;
+    }
+
+    assert(size == hdr_size);
+
+    msg_size = mbuf_hdr_get_msg_size(&hdr, mbuf->order);
+
+    if (msg_size > *sizep) {
+        error = EMSGSIZE;
+        goto out;
+    }
+
+    size = msg_size;
+    error = cbuf_read(&mbuf->cbuf, *indexp + hdr_size, buf, &size);
+
+    if (error) {
+        goto out;
+    }
+
+    assert(size == msg_size);
+
+    *indexp += hdr_size + size;
+
+out:
+    *sizep = msg_size;
+    return error;
+}