async-append: New library to allow asynchronous appending to a log file.

[sliver-openvswitch.git] / lib / async-append-aio.c

diff --git a/lib/async-append-aio.c b/lib/async-append-aio.c
new file mode 100644 (file)
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--- /dev/null
+++ b/lib/async-append-aio.c
@@ -0,0 +1,178 @@
+/* Copyright (c) 2013 Nicira, Inc.
+ *
+ * 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.
+ */
+
+#include <config.h>
+
+/* This implementation of the async-append.h interface uses the POSIX
+ * asynchronous I/O interface.  */
+
+#include "async-append.h"
+
+#include <aio.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "byteq.h"
+#include "ovs-thread.h"
+#include "util.h"
+
+/* Maximum number of bytes of buffered data. */
+enum { BUFFER_SIZE = 65536 };
+
+/* Maximum number of aiocbs to use.
+ *
+ * aiocbs are big (144 bytes with glibc 2.11 on i386) so we try to allow for a
+ * reasonable number by basing the number we allocate on the amount of buffer
+ * space. */
+enum { MAX_CBS = ROUND_DOWN_POW2(BUFFER_SIZE / sizeof(struct aiocb)) };
+BUILD_ASSERT_DECL(IS_POW2(MAX_CBS));
+
+struct async_append {
+    int fd;
+
+    struct aiocb *aiocbs;
+    unsigned int aiocb_head, aiocb_tail;
+
+    uint8_t *buffer;
+    struct byteq byteq;
+};
+
+static bool async_append_enabled;
+
+void
+async_append_enable(void)
+{
+    assert_single_threaded();
+    forbid_forking("async i/o enabled");
+    async_append_enabled = true;
+}
+
+struct async_append *
+async_append_create(int fd)
+{
+    struct async_append *ap;
+
+    ap = xmalloc(sizeof *ap);
+    ap->fd = fd;
+    ap->aiocbs = xmalloc(MAX_CBS * sizeof *ap->aiocbs);
+    ap->aiocb_head = ap->aiocb_tail = 0;
+    ap->buffer = xmalloc(BUFFER_SIZE);
+    byteq_init(&ap->byteq, ap->buffer, BUFFER_SIZE);
+
+    return ap;
+}
+
+void
+async_append_destroy(struct async_append *ap)
+{
+    if (ap) {
+        async_append_flush(ap);
+        free(ap->aiocbs);
+        free(ap->buffer);
+        free(ap);
+    }
+}
+
+static bool
+async_append_is_full(const struct async_append *ap)
+{
+    return (ap->aiocb_head - ap->aiocb_tail >= MAX_CBS
+            || byteq_is_full(&ap->byteq));
+}
+
+static bool
+async_append_is_empty(const struct async_append *ap)
+{
+    return byteq_is_empty(&ap->byteq);
+}
+
+static void
+async_append_wait(struct async_append *ap)
+{
+    int n = 0;
+
+    while (!async_append_is_empty(ap)) {
+        struct aiocb *aiocb = &ap->aiocbs[ap->aiocb_tail & (MAX_CBS - 1)];
+        int error = aio_error(aiocb);
+
+        if (error == EINPROGRESS) {
+            const struct aiocb *p = aiocb;
+            if (n > 0) {
+                return;
+            }
+            aio_suspend(&p, 1, NULL);
+        } else {
+            ignore(aio_return(aiocb));
+            ap->aiocb_tail++;
+            byteq_advance_tail(&ap->byteq, aiocb->aio_nbytes);
+            n++;
+        }
+    }
+}
+
+void
+async_append_write(struct async_append *ap, const void *data_, size_t size)
+{
+    const uint8_t *data = data_;
+
+    if (!async_append_enabled) {
+        ignore(write(ap->fd, data, size));
+        return;
+    }
+
+    while (size > 0) {
+        struct aiocb *aiocb;
+        size_t chunk_size;
+        void *chunk;
+
+        while (async_append_is_full(ap)) {
+            async_append_wait(ap);
+        }
+
+        chunk = byteq_head(&ap->byteq);
+        chunk_size = byteq_headroom(&ap->byteq);
+        if (chunk_size > size) {
+            chunk_size = size;
+        }
+        memcpy(chunk, data, chunk_size);
+
+        aiocb = &ap->aiocbs[ap->aiocb_head & (MAX_CBS - 1)];
+        memset(aiocb, 0, sizeof *aiocb);
+        aiocb->aio_fildes = ap->fd;
+        aiocb->aio_offset = 0;
+        aiocb->aio_buf = chunk;
+        aiocb->aio_nbytes = chunk_size;
+        aiocb->aio_sigevent.sigev_notify = SIGEV_NONE;
+        if (aio_write(aiocb) == -1) {
+            async_append_flush(ap);
+            ignore(write(ap->fd, data, size));
+            return;
+        }
+
+        data += chunk_size;
+        size -= chunk_size;
+        byteq_advance_head(&ap->byteq, chunk_size);
+        ap->aiocb_head++;
+    }
+}
+
+void
+async_append_flush(struct async_append *ap)
+{
+    while (!async_append_is_empty(ap)) {
+        async_append_wait(ap);
+    }
+}