Limit size of bitmap to 2million chunks.

When creating a file bitmap, choose a default size that
results in fewer than 2^21 chunks.  Without this kmalloc
failure in the kernel becomes likely.

Signed-off-by: Neil Brown <neilb@suse.de>

1 files changed, 11 insertions, 0 deletions

diff --git a/bitmap.c b/bitmap.c
index 33deab1..75492f7 100644
--- a/bitmap.c
+++ b/bitmap.c
@@ -341,6 +341,17 @@ int CreateBitmap(char *filename, int force, char uuid[16],
 		return rv;
 	}
 
+	if (chunksize == UnSet) {
+		/* We don't want more than 2^21 chunks, as 2^11 fill up one
+		 * 4K page (2 bytes per chunk), and 2^10 address of those
+		 * fill up a 4K indexing page.  2^20 might be safer...
+		 */
+		chunksize = DEFAULT_BITMAP_CHUNK;
+		/* <<21 for 2^21 chunks, >>9 to convert bytes to sectors */
+		while (array_size > (chunksize << (21-9)))
+			chunksize <<= 1;
+	}
+
 	memset(&sb, 0, sizeof(sb));
 	sb.magic = BITMAP_MAGIC;
 	sb.version = major;