Use O_DIRECT for all IO to devices.

Using buffered IO risks non-atomic updates to parts of the
device that we don't actually want to write to.  This isn't in
general safe.
So switch to O_DIRECT for all that IO and make sure we have
properly aligned buffers.

1 files changed, 2 insertions, 4 deletions

diff --git a/bitmap.c b/bitmap.c
index fdf8884..8617669 100644
--- a/bitmap.c
+++ b/bitmap.c
@@ -122,11 +122,10 @@ bitmap_info_t *bitmap_fd_read(int fd, int brief)
 	 */
 	unsigned long long total_bits = 0, read_bits = 0, dirty_bits = 0;
 	bitmap_info_t *info;
-	char *buf, *unaligned;
+	void *buf;
 	int n, skip;
 
-	unaligned = malloc(8192*2);
-	buf = (char*) ((unsigned long)unaligned | 8191)+1;
+	posix_memalign(&buf, 512, 8192);
 	n = read(fd, buf, 8192);
 
 	info = malloc(sizeof(*info));
@@ -145,7 +144,6 @@ bitmap_info_t *bitmap_fd_read(int fd, int brief)
 		fprintf(stderr, Name ": failed to read superblock of bitmap "
 			"file: %s\n", strerror(errno));
 		free(info);
-		free(unaligned);
 		return NULL;
 	}
 	memcpy(&info->sb, buf, sizeof(info->sb));