1 /* Blue Sky: File Systems in the Cloud
3 * Copyright (C) 2010 The Regents of the University of California
4 * Written by Michael Vrable <mvrable@cs.ucsd.edu>
10 #define _ATFILE_SOURCE
18 #include <sys/types.h>
23 #include "bluesky-private.h"
25 /* The logging layer for BlueSky. This is used to write filesystem changes
26 * durably to disk so that they can be recovered in the event of a system
29 /* The logging layer takes care out writing out a sequence of log records to
30 * disk. On disk, each record consists of a header, a data payload, and a
31 * footer. The footer contains a checksum of the record, meant to help with
32 * identifying corrupt log records (we would assume because the log record was
33 * only incompletely written out before a crash, which should only happen for
34 * log records that were not considered committed). */
36 // Rough size limit for a log segment. This is not a firm limit and there are
37 // no absolute guarantees on the size of a log segment.
38 #define LOG_SEGMENT_SIZE (1 << 20)
40 static void writebuf(int fd, const char *buf, size_t len)
44 written = write(fd, buf, len);
45 if (written < 0 && errno == EINTR)
47 g_assert(written >= 0);
53 /* All log writes (at least for a single log) are made by one thread, so we
54 * don't need to worry about concurrent access to the log file. Log items to
55 * write are pulled off a queue (and so may be posted by any thread).
56 * fdatasync() is used to ensure the log items are stable on disk.
58 * The log is broken up into separate files, roughly of size LOG_SEGMENT_SIZE
59 * each. If a log segment is not currently open (log->fd is negative), a new
60 * one is created. Log segment filenames are assigned sequentially.
62 * Log replay ought to be implemented later, and ought to set the initial
63 * sequence number appropriately.
65 static gpointer log_thread(gpointer d)
67 BlueSkyLog *log = (BlueSkyLog *)d;
69 int dirfd = open(log->log_directory, O_DIRECTORY);
71 fprintf(stderr, "Unable to open logging directory: %m\n");
78 g_snprintf(logfile, sizeof(logfile), "log-%08d", log->seq_num);
79 log->fd = openat(dirfd, logfile, O_CREAT|O_WRONLY|O_EXCL, 0600);
80 if (log->fd < 0 && errno == EEXIST) {
81 fprintf(stderr, "Log file %s already exists...\n", logfile);
84 } else if (log->fd < 0) {
85 fprintf(stderr, "Error opening logfile %s: %m\n", logfile);
92 BlueSkyLogItem *item = (BlueSkyLogItem *)g_async_queue_pop(log->queue);
93 g_mutex_lock(item->lock);
94 writebuf(log->fd, item->key, strlen(item->key));
95 writebuf(log->fd, item->data->data, item->data->len);
97 item->committed = TRUE;
98 g_cond_signal(item->cond);
99 g_mutex_unlock(item->lock);
101 off_t logsize = lseek(log->fd, 0, SEEK_CUR);
102 if (logsize < 0 || logsize >= LOG_SEGMENT_SIZE) {
112 BlueSkyLog *bluesky_log_new(const char *log_directory)
114 BlueSkyLog *log = g_new0(BlueSkyLog, 1);
116 log->log_directory = g_strdup(log_directory);
119 log->queue = g_async_queue_new();
121 g_thread_create(log_thread, log, FALSE, NULL);
126 BlueSkyLogItem *bluesky_log_item_new()
128 BlueSkyLogItem *item = g_new(BlueSkyLogItem, 1);
129 item->committed = FALSE;
130 item->lock = g_mutex_new();
131 item->cond = g_cond_new();
137 void bluesky_log_item_submit(BlueSkyLogItem *item, BlueSkyLog *log)
139 g_async_queue_push(log->queue, item);
142 static void bluesky_log_item_free(BlueSkyLogItem *item)
145 bluesky_string_unref(item->data);
146 g_mutex_free(item->lock);
147 g_cond_free(item->cond);
151 void bluesky_log_item_finish(BlueSkyLogItem *item)
153 g_mutex_lock(item->lock);
154 while (!item->committed)
155 g_cond_wait(item->cond, item->lock);
156 g_mutex_unlock(item->lock);
157 bluesky_log_item_free(item);