Work to allow mmap-ed log entries to be used for data blocks.

[bluesky.git] / bluesky / log.c

diff --git a/bluesky/log.c b/bluesky/log.c
index e9af52a..152f598 100644 (file)
--- a/bluesky/log.c
+++ b/bluesky/log.c
@@ -19,6 +19,7 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <sys/mman.h>
 
 #include "bluesky-private.h"
 
@@ -222,3 +223,57 @@ void bluesky_log_finish_all(GList *log_items)
         log_items = g_list_delete_link(log_items, log_items);
     }
 }
+
+/* Memory-map the given log object into memory (read-only) and return a pointer
+ * to it.  FIXME: Use some type of cache, map entire log segments, and use
+ * reference counting? */
+static int page_size = 0;
+
+BlueSkyRCStr *bluesky_log_map_object(BlueSkyLog *log,
+                                     int log_seq, int log_offset, int log_size)
+{
+    if (page_size == 0) {
+        page_size = getpagesize();
+    }
+
+    int dirfd = open(log->log_directory, O_DIRECTORY);
+    if (dirfd < 0) {
+        fprintf(stderr, "Unable to open logging directory: %m\n");
+        return NULL;
+    }
+
+    char logfile[64];
+    g_snprintf(logfile, sizeof(logfile), "log-%08d", log_seq);
+    int fd = openat(dirfd, logfile, O_RDONLY);
+    close(dirfd);
+
+    if (fd < 0) {
+        fprintf(stderr, "Error opening logfile %s: %m\n", logfile);
+        return NULL;
+    }
+
+    off_t off_start, off_end;
+    off_start = log_offset;
+    off_end = off_start + log_size;
+    off_start &= ~(page_size - 1);
+    off_end = (off_end + (page_size - 1)) & (page_size - 1);
+
+    const char *ptr = (const char *)mmap(NULL, off_end - off_start, PROT_READ,
+                                         MAP_SHARED, fd, off_start);
+
+    if (ptr == NULL) {
+        fprintf(stderr, "Error mapping logfile: %m\n");
+        close(fd);
+        return NULL;
+    }
+
+    close(fd);
+
+    BlueSkyMmap *mmap = g_new0(BlueSkyMmap, 1);
+    mmap->addr = ptr;
+    mmap->len = off_end - off_start;
+    g_atomic_int_set(&mmap->refcount, 1);
+
+    return bluesky_string_new_from_mmap(mmap,
+                                        log_offset - off_start, log_size);
+}