[cdi-devel] [PATCH] libext2: Don't destroy boot loader

[Kevin Wolf <kevin@xxxxxxxxxx>]

The first 1024 bytes on the disk must be left alone. If they are part of
the first block, they need to be included in the write request of each
superblock update because the cache works only at the granularity of
filesystem blocks.

Signed-off-by: Kevin Wolf <kevin@xxxxxxxxxx>
---

Imported from libext2.git, translated commit message for cdi.git

 ext2/libext2/fs.c           |   21 +++++++++++++++++----
 ext2/libext2/include/ext2.h |    3 +++
 ext2/libext2/superblock.c   |   14 ++++++++++++--
 3 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/ext2/libext2/fs.c b/ext2/libext2/fs.c
index 33b033f..e5c5482 100644
--- a/ext2/libext2/fs.c
+++ b/ext2/libext2/fs.c
@@ -66,11 +66,18 @@ static int fs_check_fast(ext2_fs_t* fs)
 int ext2_fs_mount(ext2_fs_t* fs)
 {
     fs->sb = malloc(sizeof(ext2_superblock_t));
+    fs->boot_sectors = malloc(1024);
+
+    if (!fs->sb || !fs->boot_sectors) {
+        goto fail;
+    }
 
     if (!ext2_sb_read(fs, fs->sb)) {
-        free(fs->sb);
-        fs->sb = NULL;
-        return 0;
+        goto fail;
+    }
+
+    if (!fs->dev_read(0, 1024, fs->boot_sectors, fs->dev_private)) {
+        goto fail;
     }
 
     fs->cache_handle = fs->cache_create(fs, ext2_sb_blocksize(fs->sb));
@@ -88,6 +95,12 @@ int ext2_fs_mount(ext2_fs_t* fs)
     }
 #endif
     return 1;
+
+fail:
+    free(fs->boot_sectors);
+    free(fs->sb);
+    fs->sb = NULL;
+    return 0;
 }
 
 int ext2_fs_unmount(ext2_fs_t* fs)
@@ -97,6 +110,7 @@ int ext2_fs_unmount(ext2_fs_t* fs)
         return 0;
     }
 
+    free(fs->boot_sectors);
     free(fs->sb);
     fs->cache_destroy(fs->cache_handle);
     fs->sb = fs->cache_handle = NULL;
@@ -107,4 +121,3 @@ void ext2_fs_sync(ext2_fs_t* fs)
 {
     fs->cache_sync(fs->cache_handle);
 }
-
diff --git a/ext2/libext2/include/ext2.h b/ext2/libext2/include/ext2.h
index cde8b41..6dc0ab0 100644
--- a/ext2/libext2/include/ext2.h
+++ b/ext2/libext2/include/ext2.h
@@ -158,6 +158,9 @@ typedef struct ext2_fs {
 
     /// Letzte allozierte Blocknummer
     uint64_t block_prev_alloc;
+
+    /// Der Inhalt der ersten 1024 Bytes auf dem Gerät
+    void* boot_sectors;
 } ext2_fs_t;
 
 /**
diff --git a/ext2/libext2/superblock.c b/ext2/libext2/superblock.c
index 973b26e..5e9e3d5 100644
--- a/ext2/libext2/superblock.c
+++ b/ext2/libext2/superblock.c
@@ -130,8 +130,18 @@ int ext2_sb_update(ext2_fs_t* fs, ext2_superblock_t* sb)
             blocks_per_group) * block_size;
 
         block = fs->cache_block(fs->cache_handle, start / block_size, 1);
-        memcpy(block->data + (start % block_size), sb,
-            sizeof(ext2_superblock_t));
+        if (i == 0 && block_size > 1024) {
+            memcpy(block->data, fs->boot_sectors, 1024);
+            memcpy(block->data + 1024, sb, sizeof(ext2_superblock_t));
+            memset(block->data + 1024 + sizeof(ext2_superblock_t), 0,
+                   block_size - 1024 - sizeof(ext2_superblock_t));
+        } else if (i == 0) {
+            memcpy(block->data, sb, sizeof(ext2_superblock_t));
+        } else {
+            memcpy(block->data, sb, sizeof(ext2_superblock_t));
+            memset(block->data + sizeof(ext2_superblock_t), 0,
+                   block_size - sizeof(ext2_superblock_t));
+        }
         fs->cache_block_free(block, 1);
     }
 
-- 
1.7.7