ext4: Fix handling of sparse files

A sparse file may have regions not mapped by any extents, at the start
or at the end of the file, or anywhere between, thus not finding a
matching extent region is never an error.

Found by python filesystem tests.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>

diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 4248ac1..bfebe7e 100644 (file)
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -1617,12 +1617,13 @@ long int read_allocated_block(struct ext2_inode *inode, int fileblock)
                - get_fs()->dev_desc->log2blksz;
 
        if (le32_to_cpu(inode->flags) & EXT4_EXTENTS_FL) {
+               long int startblock, endblock;
                char *buf = zalloc(blksz);
                if (!buf)
                        return -ENOMEM;
                struct ext4_extent_header *ext_block;
                struct ext4_extent *extent;
-               int i = -1;
+               int i;
                ext_block =
                        ext4fs_get_extent_block(ext4fs_root, buf,
                                                (struct ext4_extent_header *)
@@ -1636,28 +1637,26 @@ long int read_allocated_block(struct ext2_inode *inode, int fileblock)
 
                extent = (struct ext4_extent *)(ext_block + 1);
 
-               do {
-                       i++;
-                       if (i >= le16_to_cpu(ext_block->eh_entries))
-                               break;
-               } while (fileblock >= le32_to_cpu(extent[i].ee_block));
-               if (--i >= 0) {
-                       fileblock -= le32_to_cpu(extent[i].ee_block);
-                       if (fileblock >= le16_to_cpu(extent[i].ee_len)) {
+               for (i = 0; i < le16_to_cpu(ext_block->eh_entries); i++) {
+                       startblock = le32_to_cpu(extent[i].ee_block);
+                       endblock = startblock + le16_to_cpu(extent[i].ee_len);
+
+                       if (startblock > fileblock) {
+                               /* Sparse file */
                                free(buf);
                                return 0;
-                       }
 
-                       start = le16_to_cpu(extent[i].ee_start_hi);
-                       start = (start << 32) +
+                       } else if (fileblock < endblock) {
+                               start = le16_to_cpu(extent[i].ee_start_hi);
+                               start = (start << 32) +
                                        le32_to_cpu(extent[i].ee_start_lo);
-                       free(buf);
-                       return fileblock + start;
+                               free(buf);
+                               return (fileblock - startblock) + start;
+                       }
                }
 
-               printf("Extent Error\n");
                free(buf);
-               return -1;
+               return 0;
        }
 
        /* Direct blocks. */