libext2fs: read the block group descriptors more efficiently

When opening a filesystem, make ext2fs_open2() much more efficient by
reading the normal block group descriptors all at once, instead of one
block at a time.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index f6fe3f0..1ca63db 100644 (file)
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -84,7 +84,7 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
 {
        ext2_filsys     fs;
        errcode_t       retval;
-       unsigned long   i;
+       unsigned long   i, first_meta_bg;
        __u32           features;
        int             groups_per_block, blocks_per_group, io_flags;
        blk_t           group_block, blk;
@@ -304,7 +304,23 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
                group_block = fs->super->s_first_data_block;
        dest = (char *) fs->group_desc;
        groups_per_block = EXT2_DESC_PER_BLOCK(fs->super);
-       for (i=0 ; i < fs->desc_blocks; i++) {
+       if (fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG)
+               first_meta_bg = fs->super->s_first_meta_bg;
+       else
+               first_meta_bg = fs->desc_blocks;
+       if (first_meta_bg) {
+               retval = io_channel_read_blk(fs->io, group_block+1,
+                                            first_meta_bg, dest);
+               if (retval)
+                       goto cleanup;
+#ifdef WORDS_BIGENDIAN
+               gdp = (struct ext2_group_desc *) dest;
+               for (j=0; j < groups_per_block*first_meta_bg; j++)
+                       ext2fs_swap_group_desc(gdp++);
+#endif
+               dest += fs->blocksize*first_meta_bg;
+       }
+       for (i=first_meta_bg ; i < fs->desc_blocks; i++) {
                blk = ext2fs_descriptor_block_loc(fs, group_block, i);
                retval = io_channel_read_blk(fs->io, blk, 1, dest);
                if (retval)