libext2fs: add fs_offset entry to the undo header

The fs_offset entry stores the filesystem offset. This allows for an
easy undo, because one does not have to remember/specify the
filesystem offset manually.
The fs_offset entry is implemented as a compatible feature.

Signed-off-by: Marcus Huewe <suse-tux@gmx.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/undo_io.c b/lib/ext2fs/undo_io.c
index cb8eaa8..a0f16e4 100644 (file)
--- a/lib/ext2fs/undo_io.c
+++ b/lib/ext2fs/undo_io.c
@@ -94,10 +94,12 @@ struct undo_header {
        __le32 fs_block_size;   /* block size of the target device */
        __le32 sb_crc;          /* crc32c of the superblock */
        __le32 state;           /* e2undo state flags */
-       __le32 f_compat;        /* compatible features (none so far) */
+       __le32 f_compat;        /* compatible features */
        __le32 f_incompat;      /* incompatible features (none so far) */
        __le32 f_rocompat;      /* ro compatible features (none so far) */
-       __u8 padding[448];      /* padding */
+       __le32 pad32;           /* padding for fs_offset */
+       __le64 fs_offset;       /* filesystem offset */
+       __u8 padding[436];      /* padding */
        __le32 header_crc;      /* crc32c of this header (but not this field) */
 };
 
@@ -149,6 +151,16 @@ struct undo_private_data {
 };
 #define KEYS_PER_BLOCK(d) (((d)->tdb_data_size / sizeof(struct undo_key)) - 1)
 
+#define E2UNDO_FEATURE_COMPAT_FS_OFFSET 0x1    /* the filesystem offset */
+
+static inline void e2undo_set_feature_fs_offset(struct undo_header *header) {
+       header->f_compat |= E2UNDO_FEATURE_COMPAT_FS_OFFSET;
+}
+
+static inline void e2undo_clear_feature_fs_offset(struct undo_header *header) {
+       header->f_compat &= ~E2UNDO_FEATURE_COMPAT_FS_OFFSET;
+}
+
 static io_manager undo_io_backing_manager;
 static char *tdb_file;
 static int actual_size;
@@ -222,6 +234,11 @@ static errcode_t write_undo_indexes(struct undo_private_data *data, int flush)
        data->hdr.key_offset = ext2fs_cpu_to_le64(data->first_key_blk);
        data->hdr.fs_block_size = ext2fs_cpu_to_le32(block_size);
        data->hdr.sb_crc = ext2fs_cpu_to_le32(sb_crc);
+       data->hdr.fs_offset = ext2fs_cpu_to_le64(data->offset);
+       if (data->offset)
+               e2undo_set_feature_fs_offset(&data->hdr);
+       else
+               e2undo_clear_feature_fs_offset(&data->hdr);
        hdr_crc = ext2fs_crc32c_le(~0, (unsigned char *)&data->hdr,
                                   sizeof(data->hdr) -
                                   sizeof(data->hdr.header_crc));
@@ -567,7 +584,12 @@ static errcode_t try_reopen_undo_file(int undo_fd,
        super_block = ext2fs_le64_to_cpu(hdr.super_offset);
        num_keys = ext2fs_le64_to_cpu(hdr.num_keys);
        io_channel_set_blksize(data->undo_file, blocksize);
-       if (hdr.f_compat || hdr.f_incompat || hdr.f_rocompat)
+       /*
+        * Do not compare hdr.f_compat with the available compatible
+        * features set, because a "missing" compatible feature should
+        * not cause any problems.
+        */
+       if (hdr.f_incompat || hdr.f_rocompat)
                goto bad_file;
 
        /* Superblock matches this FS? */