Add support for extents to libext2fs

[tools/e2fsprogs.git] / lib / ext2fs / ext3_extents.h

diff --git a/lib/ext2fs/ext3_extents.h b/lib/ext2fs/ext3_extents.h
index c4178c9..ba980e4 100644 (file)
--- a/lib/ext2fs/ext3_extents.h
+++ b/lib/ext2fs/ext3_extents.h
@@ -126,6 +126,26 @@ struct ext3_ext_path {
 #define EXT_MAX_BLOCK  0xffffffff
 #define EXT_CACHE_MARK 0xffff
 
+/*
+ * EXT_INIT_MAX_LEN is the maximum number of blocks we can have in an
+ * initialized extent. This is 2^15 and not (2^16 - 1), since we use the
+ * MSB of ee_len field in the extent datastructure to signify if this
+ * particular extent is an initialized extent or an uninitialized (i.e.
+ * preallocated).
+ * EXT_UNINIT_MAX_LEN is the maximum number of blocks we can have in an
+ * uninitialized extent.
+ * If ee_len is <= 0x8000, it is an initialized extent. Otherwise, it is an
+ * uninitialized one. In other words, if MSB of ee_len is set, it is an
+ * uninitialized extent with only one special scenario when ee_len = 0x8000.
+ * In this case we can not have an uninitialized extent of zero length and
+ * thus we make it as a special case of initialized extent with 0x8000 length.
+ * This way we get better extent-to-group alignment for initialized extents.
+ * Hence, the maximum number of blocks we can have in an *initialized*
+ * extent is 2^15 (32768) and in an *uninitialized* extent is 2^15-1 (32767).
+ */
+#define EXT_INIT_MAX_LEN       (1UL << 15)
+#define EXT_UNINIT_MAX_LEN     (EXT_INIT_MAX_LEN - 1)
+
 
 #define EXT_FIRST_EXTENT(__hdr__) \
        ((struct ext3_extent *) (((char *) (__hdr__)) +         \