Add support for mmaps with nonzero offset values. Needs testing.

diff --git a/buffer.c b/buffer.c
index 4f788b61623dc05684931e8ae703637707d71d6d..bad57d3f50726c53c639eef3515512db04d8905d 100644 (file)
--- a/buffer.c
+++ b/buffer.c
@@ -2617,13 +2617,25 @@ evbuffer_file_segment_new(
 #if defined(_EVENT_HAVE_MMAP)
        /* TODO: Implement an mmap-alike for windows. */
        if (!(flags & EVBUF_FS_DISABLE_MMAP)) {
-               /* some mmap implementations require offset to be a multiple of
-                * the page size.  most users of this api, are likely to use 0
-                * so mapping everything is not likely to be a problem.
-                * TODO(niels): determine page size and round offset to that
-                * page size to avoid mapping too much memory.
-                */
-               void *mapped = mmap(NULL, length + offset, PROT_READ,
+               off_t offset_rounded = 0, offset_leftover = 0;
+               void *mapped;
+               if (offset) {
+                       /* mmap implementations don't generally like us
+                        * to have an offset that isn't a round  */
+#ifdef SC_PAGE_SIZE
+                       long page_size = sysconf(SC_PAGE_SIZE);
+#elif defined(_SC_PAGE_SIZE)
+                       long page_size = sysconf(_SC_PAGE_SIZE);
+#else
+                       long page_size = 1;
+#endif
+                       if (page_size == -1)
+                               goto err;
+                       offset_leftover = offset % page_size;
+                       offset_rounded = offset - offset_leftover;
+               }
+               mapped = mmap(NULL, length + offset_leftover,
+                   PROT_READ,
 #ifdef MAP_NOCACHE
                    MAP_NOCACHE | /* ??? */
 #endif
@@ -2631,14 +2643,14 @@ evbuffer_file_segment_new(
                    MAP_FILE |
 #endif
                    MAP_PRIVATE,
-                   fd, 0);
+                   fd, offset_rounded);
                if (mapped == MAP_FAILED) {
                        event_warn("%s: mmap(%d, %d, %zu) failed",
                            __func__, fd, 0, (size_t)(offset + length));
                } else {
                        seg->mapping = mapped;
-                       seg->contents = ((char*)mapped)+offset;
-                       seg->offset = offset;
+                       seg->contents = (char*)mapped+offset_leftover;
+                       seg->offset = 0;
                        seg->type = EVBUF_FS_MMAP;
                        goto done;
                }