block: vhdx - add header update capability.
This adds the ability to update the headers in a VHDX image, including
generating a new MS-compatible GUID.
As VHDX depends on uuid.h, VHDX is now a configurable build option. If
VHDX support is enabled, that will also enable uuid as well. The
default is to have VHDX enabled.
To enable/disable VHDX: --enable-vhdx, --disable-vhdx
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/vhdx.c b/block/vhdx.c
index b497c27..7b94c42 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -22,6 +22,7 @@
#include "block/vhdx.h"
#include "migration/migration.h"
+#include <uuid/uuid.h>
/* Several metadata and region table data entries are identified by
* guids in a MS-specific GUID format. */
@@ -157,12 +158,41 @@
VHDXBatEntry *bat;
uint64_t bat_offset;
+ MSGUID session_guid;
+
+
VHDXParentLocatorHeader parent_header;
VHDXParentLocatorEntry *parent_entries;
Error *migration_blocker;
} 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)
+ *
+ * Note: The resulting checksum is in the CPU endianness, not necessarily
+ * in the file format endianness (LE). Any header export to disk should
+ * make sure that vhdx_header_le_export() is used to convert to the
+ * correct endianness
+ */
+uint32_t vhdx_update_checksum(uint8_t *buf, size_t size, int crc_offset)
+{
+ uint32_t crc;
+
+ assert(buf != NULL);
+ assert(size > (crc_offset + sizeof(crc)));
+
+ memset(buf + crc_offset, 0, sizeof(crc));
+ crc = crc32c(0xffffffff, buf, size);
+ memcpy(buf + crc_offset, &crc, sizeof(crc));
+
+ return crc;
+}
+
uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
int crc_offset)
{
@@ -214,6 +244,19 @@
/*
+ * This generates a UUID that is compliant with the MS GUIDs used
+ * in the VHDX spec (and elsewhere).
+ */
+void vhdx_guid_generate(MSGUID *guid)
+{
+ uuid_t uuid;
+ assert(guid != NULL);
+
+ uuid_generate(uuid);
+ memcpy(guid, uuid, sizeof(MSGUID));
+}
+
+/*
* 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"
@@ -251,6 +294,113 @@
le64_to_cpus(&h->log_offset);
}
+/* All VHDX structures on disk are little endian */
+static void vhdx_header_le_export(VHDXHeader *orig_h, VHDXHeader *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);
+
+ new_h->file_write_guid = orig_h->file_write_guid;
+ new_h->data_write_guid = orig_h->data_write_guid;
+ new_h->log_guid = orig_h->log_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 generate_data_write_guid)
+{
+ int ret = 0;
+ int hdr_idx = 0;
+ uint64_t header_offset = VHDX_HEADER1_OFFSET;
+
+ VHDXHeader *active_header;
+ VHDXHeader *inactive_header;
+ VHDXHeader 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 generated before any file write, including
+ * headers */
+ inactive_header->file_write_guid = s->session_guid;
+
+ /* a new data guid only needs to be generated before any guest-visible
+ * writes (i.e. something observable via virtual disk read) */
+ if (generate_data_write_guid) {
+ vhdx_guid_generate(&inactive_header->data_write_guid);
+ }
+
+ /* the header checksum is not over just the packed size of VHDXHeader,
+ * but rather over the entire 'reserved' range for the header, which is
+ * 4KB (VHDX_HEADER_SIZE). */
+
+ buffer = qemu_blockalign(bs, 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 exit;
+ }
+ /* overwrite the actual VHDXHeader portion */
+ memcpy(buffer, inactive_header, sizeof(VHDXHeader));
+ inactive_header->checksum =
+ vhdx_update_checksum(buffer, VHDX_HEADER_SIZE,
+ offsetof(VHDXHeader, checksum));
+ vhdx_header_le_export(inactive_header, &header_le);
+ ret = bdrv_pwrite_sync(bs->file, header_offset, &header_le,
+ sizeof(VHDXHeader));
+ if (ret < 0) {
+ goto exit;
+ }
+ s->curr_header = hdr_idx;
+
+exit:
+ qemu_vfree(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 generate_data_write_guid)
+{
+ int ret;
+
+ ret = vhdx_update_header(bs, s, generate_data_write_guid);
+ if (ret < 0) {
+ return ret;
+ }
+ ret = vhdx_update_header(bs, s, generate_data_write_guid);
+ return ret;
+}
/* opens the specified header block from the VHDX file header section */
static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
@@ -742,6 +892,11 @@
goto fail;
}
+ /* 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;
@@ -804,8 +959,10 @@
}
if (flags & BDRV_O_RDWR) {
- ret = -ENOTSUP;
- goto fail;
+ ret = vhdx_update_headers(bs, s, false);
+ if (ret < 0) {
+ goto fail;
+ }
}
/* TODO: differencing files, write */
