--- /dev/null
+/* Blue Sky: File Systems in the Cloud
+ *
+ * Copyright (C) 2010 The Regents of the University of California
+ * Written by Michael Vrable <mvrable@cs.ucsd.edu>
+ *
+ * TODO: Licensing
+ */
+
+#define _GNU_SOURCE
+#define _ATFILE_SOURCE
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <glib.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "bluesky-private.h"
+
+/* The logging layer for BlueSky. This is used to write filesystem changes
+ * durably to disk so that they can be recovered in the event of a system
+ * crash. */
+
+/* The logging layer takes care out writing out a sequence of log records to
+ * disk. On disk, each record consists of a header, a data payload, and a
+ * footer. The footer contains a checksum of the record, meant to help with
+ * identifying corrupt log records (we would assume because the log record was
+ * only incompletely written out before a crash, which should only happen for
+ * log records that were not considered committed). */
+
+// Rough size limit for a log segment. This is not a firm limit and there are
+// no absolute guarantees on the size of a log segment.
+#define LOG_SEGMENT_SIZE (1 << 20)
+
+static void writebuf(int fd, const char *buf, size_t len)
+{
+ while (len > 0) {
+ ssize_t written;
+ written = write(fd, buf, len);
+ if (written < 0 && errno == EINTR)
+ continue;
+ g_assert(written >= 0);
+ buf += written;
+ len -= written;
+ }
+}
+
+/* All log writes (at least for a single log) are made by one thread, so we
+ * don't need to worry about concurrent access to the log file. Log items to
+ * write are pulled off a queue (and so may be posted by any thread).
+ * fdatasync() is used to ensure the log items are stable on disk.
+ *
+ * The log is broken up into separate files, roughly of size LOG_SEGMENT_SIZE
+ * each. If a log segment is not currently open (log->fd is negative), a new
+ * one is created. Log segment filenames are assigned sequentially.
+ *
+ * Log replay ought to be implemented later, and ought to set the initial
+ * sequence number appropriately.
+ */
+static gpointer log_thread(gpointer d)
+{
+ BlueSkyLog *log = (BlueSkyLog *)d;
+
+ int dirfd = open(log->log_directory, O_DIRECTORY);
+ if (dirfd < 0) {
+ fprintf(stderr, "Unable to open logging directory: %m\n");
+ return NULL;
+ }
+
+ while (TRUE) {
+ if (log->fd < 0) {
+ char logfile[64];
+ g_snprintf(logfile, sizeof(logfile), "log-%08d", log->seq_num);
+ log->fd = openat(dirfd, logfile, O_CREAT|O_WRONLY|O_EXCL, 0600);
+ if (log->fd < 0 && errno == EEXIST) {
+ fprintf(stderr, "Log file %s already exists...\n", logfile);
+ log->seq_num++;
+ continue;
+ } else if (log->fd < 0) {
+ fprintf(stderr, "Error opening logfile %s: %m\n", logfile);
+ return NULL;
+ }
+ fsync(log->fd);
+ fsync(dirfd);
+ }
+
+ BlueSkyLogItem *item = (BlueSkyLogItem *)g_async_queue_pop(log->queue);
+ g_mutex_lock(item->lock);
+ writebuf(log->fd, item->key, strlen(item->key));
+ writebuf(log->fd, item->data->data, item->data->len);
+ fdatasync(log->fd);
+ item->committed = TRUE;
+ g_cond_signal(item->cond);
+ g_mutex_unlock(item->lock);
+
+ off_t logsize = lseek(log->fd, 0, SEEK_CUR);
+ if (logsize < 0 || logsize >= LOG_SEGMENT_SIZE) {
+ close(log->fd);
+ log->fd = -1;
+ log->seq_num++;
+ }
+ }
+
+ return NULL;
+}
+
+BlueSkyLog *bluesky_log_new(const char *log_directory)
+{
+ BlueSkyLog *log = g_new0(BlueSkyLog, 1);
+
+ log->log_directory = g_strdup(log_directory);
+ log->fd = -1;
+ log->seq_num = 0;
+ log->queue = g_async_queue_new();
+
+ g_thread_create(log_thread, log, FALSE, NULL);
+
+ return log;
+}
+
+BlueSkyLogItem *bluesky_log_item_new()
+{
+ BlueSkyLogItem *item = g_new(BlueSkyLogItem, 1);
+ item->committed = FALSE;
+ item->lock = g_mutex_new();
+ item->cond = g_cond_new();
+ item->key = NULL;
+ item->data = NULL;
+ return item;
+}
+
+void bluesky_log_item_submit(BlueSkyLogItem *item, BlueSkyLog *log)
+{
+ g_async_queue_push(log->queue, item);
+}
+
+static void bluesky_log_item_free(BlueSkyLogItem *item)
+{
+ g_free(item->key);
+ bluesky_string_unref(item->data);
+ g_mutex_free(item->lock);
+ g_cond_free(item->cond);
+ g_free(item);
+}
+
+void bluesky_log_item_finish(BlueSkyLogItem *item)
+{
+ g_mutex_lock(item->lock);
+ while (!item->committed)
+ g_cond_wait(item->cond, item->lock);
+ g_mutex_unlock(item->lock);
+ bluesky_log_item_free(item);
+}
projects / bluesky.git / commitdiff