This adds the ability to update the headers in a VHDX image, including
generating a new MS-compatible GUID, and checksum.
Signed-off-by: Jeff Cody <jc...@redhat.com>
---
block/vhdx.c | 165 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 163 insertions(+), 2 deletions(-)
diff --git a/block/vhdx.c b/block/vhdx.c
index 97775d2..13d1e7f 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -27,6 +27,11 @@
le16_to_cpus(&(guid)->data2); \
le16_to_cpus(&(guid)->data3); } while (0)
+#define cpu_to_leguids(guid) do { \
+ cpu_to_le32s(&(guid)->data1); \
+ cpu_to_le16s(&(guid)->data2); \
+ cpu_to_le16s(&(guid)->data3); } while (0)
+
/* Several metadata and region table data entries are identified by
* guids in a MS-specific GUID format. */
@@ -160,11 +165,35 @@ typedef struct BDRVVHDXState {
vhdx_bat_entry *bat;
uint64_t bat_offset;
+ ms_guid session_guid;
+
+
vhdx_parent_locator_header parent_header;
vhdx_parent_locator_entry *parent_entries;
} BDRVVHDXState;
+/* Calculates new checksum.
+ *
+ * Zero is substituted during crc calculation for the original crc field
+ * crc_offset: byte offset in buf of the buffer crc
+ * buf: buffer pointer
+ * size: size of buffer (must be > crc_offset+4)
+ */
+static uint32_t vhdx_update_checksum(uint8_t *buf, size_t size, int crc_offset)
+{
+ uint32_t crc;
+
+ assert(buf != NULL);
+ assert(size > (crc_offset+4));
+
+ memset(buf+crc_offset, 0, sizeof(crc));
+ crc = crc32c(0xffffffff, buf, size);
+ memcpy(buf+crc_offset, &crc, sizeof(crc));
+
+ return crc;
+}
+
/* Validates the checksum of the buffer, with an in-place CRC.
*
* Zero is substituted during crc calculation for the original crc field,
@@ -198,6 +227,33 @@ static bool vhdx_checksum_is_valid(uint8_t *buf, size_t
size, int crc_offset)
}
/*
+ * This generates a UUID that is compliant with the MS GUIDs used
+ * in the VHDX spec (and elsewhere).
+ *
+ * We can do this with uuid_generate if uuid.h is present,
+ * however not all systems have uuid and the generation is
+ * pretty straightforward for the DCE + random usage case
+ *
+ */
+static void vhdx_guid_generate(ms_guid *guid)
+{
+ assert(guid != NULL);
+
+ int i;
+
+ guid->data1 = g_random_int();
+ guid->data2 = g_random_int_range(0, 0xffff);
+ guid->data3 = g_random_int_range(0, 0x0fff);
+ guid->data3 |= 0x4000; /* denotes random algorithm */
+
+ guid->data4[0] = g_random_int_range(0, 0x3f);
+ guid->data4[0] |= 0x80; /* denotes DCE type */
+ for (i = 1; i < sizeof(guid->data4); i++) {
+ guid->data4[i] = g_random_int_range(0, 0xff);
+ }
+}
+
+/*
* Per the MS VHDX Specification, for every VHDX file:
* - The header section is fixed size - 1 MB
* - The header section is always the first "object"
@@ -236,6 +292,107 @@ static void vhdx_header_le_import(vhdx_header *h)
le64_to_cpus(&h->log_offset);
}
+/* All VHDX structures on disk are little endian */
+static void vhdx_header_le_export(vhdx_header *orig_h, vhdx_header *new_h)
+{
+ assert(orig_h != NULL);
+ assert(new_h != NULL);
+
+ new_h->signature = cpu_to_le32(orig_h->signature);
+ new_h->checksum = cpu_to_le32(orig_h->checksum);
+ new_h->sequence_number = cpu_to_le64(orig_h->sequence_number);
+
+ memcpy(&new_h->file_write_guid, &orig_h->file_write_guid, sizeof(ms_guid));
+ memcpy(&new_h->data_write_guid, &orig_h->data_write_guid, sizeof(ms_guid));
+ memcpy(&new_h->log_guid, &orig_h->log_guid, sizeof(ms_guid));
+
+ cpu_to_leguids(&new_h->file_write_guid);
+ cpu_to_leguids(&new_h->data_write_guid);
+ cpu_to_leguids(&new_h->log_guid);
+
+ new_h->log_version = cpu_to_le16(orig_h->log_version);
+ new_h->version = cpu_to_le16(orig_h->version);
+ new_h->log_length = cpu_to_le32(orig_h->log_length);
+ new_h->log_offset = cpu_to_le64(orig_h->log_offset);
+}
+
+/* Update the VHDX headers
+ *
+ * This follows the VHDX spec procedures for header updates.
+ *
+ * - non-current header is updated with largest sequence number
+ */
+static int vhdx_update_header(BlockDriverState *bs, BDRVVHDXState *s, bool rw)
+{
+ int ret = 0;
+ int hdr_idx = 0;
+ uint64_t header_offset = VHDX_HEADER1_OFFSET;
+
+ vhdx_header *active_header;
+ vhdx_header *inactive_header;
+ vhdx_header header_le;
+ uint8_t *buffer;
+
+ /* operate on the non-current header */
+ if (s->curr_header == 0) {
+ hdr_idx = 1;
+ header_offset = VHDX_HEADER2_OFFSET;
+ }
+
+ active_header = s->headers[s->curr_header];
+ inactive_header = s->headers[hdr_idx];
+
+ inactive_header->sequence_number = active_header->sequence_number + 1;
+
+ /* a new file guid must be generate before any file write, including
+ * headers */
+ memcpy(&inactive_header->file_write_guid, &s->session_guid,
+ sizeof(ms_guid));
+
+ /* a new data guid only needs to be generate before any guest-visisble
+ * writes, so update it if the image is opened r/w. */
+ if (rw) {
+ vhdx_guid_generate(&inactive_header->data_write_guid);
+ }
+
+ /* the header checksum is not over just the packed size of vhdx_header,
+ * but rather over the entire 'reserved' range for the header, which is
+ * 4KB (VHDX_HEADER_SIZE). */
+
+ buffer = g_malloc(VHDX_HEADER_SIZE);
+ /* we can't assume the extra reserved bytes are 0 */
+ ret = bdrv_pread(bs->file, header_offset, buffer, VHDX_HEADER_SIZE);
+ if (ret < 0) {
+ goto fail;
+ }
+ /* overwrite the actual vhdx_header portion */
+ memcpy(buffer, inactive_header, sizeof(vhdx_header));
+ inactive_header->checksum = vhdx_update_checksum(buffer,
+ VHDX_HEADER_SIZE, 4);
+ vhdx_header_le_export(inactive_header, &header_le);
+ bdrv_pwrite_sync(bs->file, header_offset, &header_le, sizeof(vhdx_header));
+ s->curr_header = hdr_idx;
+
+fail:
+ g_free(buffer);
+ return ret;
+}
+
+/*
+ * The VHDX spec calls for header updates to be performed twice, so that both
+ * the current and non-current header have valid info
+ */
+static int vhdx_update_headers(BlockDriverState *bs, BDRVVHDXState *s, bool rw)
+{
+ int ret;
+
+ ret = vhdx_update_header(bs, s, rw);
+ if (ret < 0) {
+ return ret;
+ }
+ ret = vhdx_update_header(bs, s, rw);
+ return ret;
+}
/* opens the specified header block from the VHDX file header section */
static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
@@ -628,6 +785,11 @@ static int vhdx_open(BlockDriverState *bs, int flags)
qemu_co_mutex_init(&s->lock);
+ /* This is used for any header updates, for the file_write_guid.
+ * The spec dictates that a new value should be used for the first
+ * header update */
+ vhdx_guid_generate(&s->session_guid);
+
ret = vhdx_parse_header(bs, s);
if (ret) {
goto fail;
@@ -664,8 +826,7 @@ static int vhdx_open(BlockDriverState *bs, int flags)
}
if (flags & BDRV_O_RDWR) {
- ret = -ENOTSUP;
- goto fail;
+ vhdx_update_headers(bs, s, false);
}
/* TODO: differencing files, write */
--
1.8.1.4
