shared: add ring buffer

New "struct ring" object that implements a basic ring buffer for arbitrary
byte-streams. A new basic runtime test is also added.

This will be needed for our pty helpers for systemd-console and friends.

3 files changed, 402 insertions, 0 deletions

diff --git a/src/shared/ring.c b/src/shared/ring.c
new file mode 100644
index 0000000000..8ae61234c7
--- /dev/null
+++ b/src/shared/ring.c
@@ -0,0 +1,208 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/uio.h>
+#include "macro.h"
+#include "ring.h"
+
+#define RING_MASK(_r, _v) ((_v) & ((_r)->size - 1))
+
+void ring_flush(struct ring *r) {
+        assert(r);
+
+        r->start = 0;
+        r->used = 0;
+}
+
+void ring_clear(struct ring *r) {
+        free(r->buf);
+        zero(*r);
+}
+
+/*
+ * Get data pointers for current ring-buffer data. @vec must be an array of 2
+ * iovec objects. They are filled according to the data available in the
+ * ring-buffer. 0, 1 or 2 is returned according to the number of iovec objects
+ * that were filled (0 meaning buffer is empty).
+ *
+ * Hint: "struct iovec" is defined in <sys/uio.h> and looks like this:
+ *     struct iovec {
+ *         void *iov_base;
+ *         size_t iov_len;
+ *     };
+ */
+size_t ring_peek(struct ring *r, struct iovec *vec) {
+        assert(r);
+
+        if (r->used == 0) {
+                return 0;
+        } else if (r->start + r->used <= r->size) {
+                if (vec) {
+                        vec[0].iov_base = &r->buf[r->start];
+                        vec[0].iov_len = r->used;
+                }
+                return 1;
+        } else {
+                if (vec) {
+                        vec[0].iov_base = &r->buf[r->start];
+                        vec[0].iov_len = r->size - r->start;
+                        vec[1].iov_base = r->buf;
+                        vec[1].iov_len = r->used - (r->size - r->start);
+                }
+                return 2;
+        }
+}
+
+/*
+ * Copy data from the ring buffer into the linear external buffer @buf. Copy
+ * at most @size bytes. If the ring buffer size is smaller, copy less bytes and
+ * return the number of bytes copied.
+ */
+size_t ring_copy(struct ring *r, void *buf, size_t size) {
+        size_t l;
+
+        assert(r);
+        assert(buf);
+
+        if (size > r->used)
+                size = r->used;
+
+        if (size > 0) {
+                l = r->size - r->start;
+                if (size <= l) {
+                        memcpy(buf, &r->buf[r->start], size);
+                } else {
+                        memcpy(buf, &r->buf[r->start], l);
+                        memcpy((uint8_t*)buf + l, r->buf, size - l);
+                }
+        }
+
+        return size;
+}
+
+/*
+ * Resize ring-buffer to size @nsize. @nsize must be a power-of-2, otherwise
+ * ring operations will behave incorrectly.
+ */
+static int ring_resize(struct ring *r, size_t nsize) {
+        uint8_t *buf;
+        size_t l;
+
+        assert(r);
+        assert(nsize > 0);
+
+        buf = malloc(nsize);
+        if (!buf)
+                return -ENOMEM;
+
+        if (r->used > 0) {
+                l = r->size - r->start;
+                if (r->used <= l) {
+                        memcpy(buf, &r->buf[r->start], r->used);
+                } else {
+                        memcpy(buf, &r->buf[r->start], l);
+                        memcpy(&buf[l], r->buf, r->used - l);
+                }
+        }
+
+        free(r->buf);
+        r->buf = buf;
+        r->size = nsize;
+        r->start = 0;
+
+        return 0;
+}
+
+/*
+ * Resize ring-buffer to provide enough room for @add bytes of new data. This
+ * resizes the buffer if it is too small. It returns -ENOMEM on OOM and 0 on
+ * success.
+ */
+static int ring_grow(struct ring *r, size_t add) {
+        size_t need;
+
+        assert(r);
+
+        if (r->size - r->used >= add)
+                return 0;
+
+        need = r->used + add;
+        if (need <= r->used)
+                return -ENOMEM;
+        else if (need < 4096)
+                need = 4096;
+
+        need = ALIGN_POWER2(need);
+        if (need == 0)
+                return -ENOMEM;
+
+        return ring_resize(r, need);
+}
+
+/*
+ * Push @len bytes from @u8 into the ring buffer. The buffer is resized if it
+ * is too small. -ENOMEM is returned on OOM, 0 on success.
+ */
+int ring_push(struct ring *r, const void *u8, size_t size) {
+        int err;
+        size_t pos, l;
+
+        assert(r);
+        assert(u8);
+
+        if (size == 0)
+                return 0;
+
+        err = ring_grow(r, size);
+        if (err < 0)
+                return err;
+
+        pos = RING_MASK(r, r->start + r->used);
+        l = r->size - pos;
+        if (l >= size) {
+                memcpy(&r->buf[pos], u8, size);
+        } else {
+                memcpy(&r->buf[pos], u8, l);
+                memcpy(r->buf, (const uint8_t*)u8 + l, size - l);
+        }
+
+        r->used += size;
+
+        return 0;
+}
+
+/*
+ * Remove @len bytes from the start of the ring-buffer. Note that we protect
+ * against overflows so removing more bytes than available is safe.
+ */
+void ring_pull(struct ring *r, size_t size) {
+        assert(r);
+
+        if (size > r->used)
+                size = r->used;
+
+        r->start = RING_MASK(r, r->start + size);
+        r->used -= size;
+}
diff --git a/src/shared/ring.h b/src/shared/ring.h
new file mode 100644
index 0000000000..6b12530e31
--- /dev/null
+++ b/src/shared/ring.h
@@ -0,0 +1,59 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/uio.h>
+
+struct ring {
+        uint8_t *buf;           /* buffer or NULL */
+        size_t size;            /* actual size of @buf */
+        size_t start;           /* start position of ring */
+        size_t used;            /* number of actually used bytes */
+};
+
+/* flush buffer so it is empty again */
+void ring_flush(struct ring *r);
+
+/* flush buffer, free allocated data and reset to initial state */
+void ring_clear(struct ring *r);
+
+/* get pointers to buffer data and their length */
+size_t ring_peek(struct ring *r, struct iovec *vec);
+
+/* copy data into external linear buffer */
+size_t ring_copy(struct ring *r, void *buf, size_t size);
+
+/* push data to the end of the buffer */
+int ring_push(struct ring *r, const void *u8, size_t size);
+
+/* pull data from the front of the buffer */
+void ring_pull(struct ring *r, size_t size);
+
+/* return size of occupied buffer in bytes */
+static inline size_t ring_get_size(struct ring *r)
+{
+        return r->used;
+}
diff --git a/src/test/test-ring.c b/src/test/test-ring.c
new file mode 100644
index 0000000000..880815811c
--- /dev/null
+++ b/src/test/test-ring.c
@@ -0,0 +1,135 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <locale.h>
+#include <errno.h>
+
+#include "def.h"
+#include "ring.h"
+#include "util.h"
+
+static void test_ring(void) {
+        static const char buf[8192];
+        struct ring r;
+        size_t l;
+        struct iovec vec[2];
+        int s;
+
+        memset(&r, 0, sizeof(r));
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 0);
+
+        s = ring_push(&r, buf, 2048);
+        assert_se(!s);
+        assert_se(ring_get_size(&r) == 2048);
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 1);
+        assert_se(vec[0].iov_len == 2048);
+        assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
+        assert_se(ring_get_size(&r) == 2048);
+
+        ring_pull(&r, 2048);
+        assert_se(ring_get_size(&r) == 0);
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 0);
+        assert_se(ring_get_size(&r) == 0);
+
+        s = ring_push(&r, buf, 2048);
+        assert_se(!s);
+        assert_se(ring_get_size(&r) == 2048);
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 1);
+        assert_se(vec[0].iov_len == 2048);
+        assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
+        assert_se(ring_get_size(&r) == 2048);
+
+        s = ring_push(&r, buf, 1);
+        assert_se(!s);
+        assert_se(ring_get_size(&r) == 2049);
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 2);
+        assert_se(vec[0].iov_len == 2048);
+        assert_se(vec[1].iov_len == 1);
+        assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
+        assert_se(!memcmp(vec[1].iov_base, buf, vec[1].iov_len));
+        assert_se(ring_get_size(&r) == 2049);
+
+        ring_pull(&r, 2048);
+        assert_se(ring_get_size(&r) == 1);
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 1);
+        assert_se(vec[0].iov_len == 1);
+        assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
+        assert_se(ring_get_size(&r) == 1);
+
+        ring_pull(&r, 1);
+        assert_se(ring_get_size(&r) == 0);
+
+        s = ring_push(&r, buf, 2048);
+        assert_se(!s);
+        assert_se(ring_get_size(&r) == 2048);
+
+        s = ring_push(&r, buf, 2049);
+        assert_se(!s);
+        assert_se(ring_get_size(&r) == 4097);
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 1);
+        assert_se(vec[0].iov_len == 4097);
+        assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
+        assert_se(ring_get_size(&r) == 4097);
+
+        ring_pull(&r, 1);
+        assert_se(ring_get_size(&r) == 4096);
+
+        s = ring_push(&r, buf, 4096);
+        assert_se(!s);
+        assert_se(ring_get_size(&r) == 8192);
+
+        l = ring_peek(&r, vec);
+        assert_se(l == 2);
+        assert_se(vec[0].iov_len == 8191);
+        assert_se(vec[1].iov_len == 1);
+        assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
+        assert_se(!memcmp(vec[1].iov_base, buf, vec[1].iov_len));
+        assert_se(ring_get_size(&r) == 8192);
+
+        ring_clear(&r);
+        assert_se(ring_get_size(&r) == 0);
+}
+
+int main(int argc, char *argv[]) {
+        log_parse_environment();
+        log_open();
+
+        test_ring();
+
+        return 0;
+}