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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>
This commit is contained in:
Jeff Cody
Stefan Hajnoczi
parent
6e9d290bf6
commit
4f18b7824a
4 changed files with 196 additions and 5 deletions
161
block/vhdx.c
161
block/vhdx.c
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@ -22,6 +22,7 @@
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#include "block/vhdx.h"
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#include "migration/migration.h"
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#include <uuid/uuid.h>
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/* Several metadata and region table data entries are identified by
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* guids in a MS-specific GUID format. */
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@ -157,12 +158,41 @@ typedef struct BDRVVHDXState {
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VHDXBatEntry *bat;
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uint64_t bat_offset;
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MSGUID session_guid;
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VHDXParentLocatorHeader parent_header;
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VHDXParentLocatorEntry *parent_entries;
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Error *migration_blocker;
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} BDRVVHDXState;
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/* Calculates new checksum.
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*
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* Zero is substituted during crc calculation for the original crc field
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* crc_offset: byte offset in buf of the buffer crc
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* buf: buffer pointer
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* size: size of buffer (must be > crc_offset+4)
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*
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* Note: The resulting checksum is in the CPU endianness, not necessarily
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* in the file format endianness (LE). Any header export to disk should
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* make sure that vhdx_header_le_export() is used to convert to the
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* correct endianness
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*/
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uint32_t vhdx_update_checksum(uint8_t *buf, size_t size, int crc_offset)
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{
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uint32_t crc;
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assert(buf != NULL);
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assert(size > (crc_offset + sizeof(crc)));
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memset(buf + crc_offset, 0, sizeof(crc));
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crc = crc32c(0xffffffff, buf, size);
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memcpy(buf + crc_offset, &crc, sizeof(crc));
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return crc;
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}
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uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
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int crc_offset)
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{
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@ -213,6 +243,19 @@ bool vhdx_checksum_is_valid(uint8_t *buf, size_t size, int crc_offset)
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}
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/*
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* This generates a UUID that is compliant with the MS GUIDs used
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* in the VHDX spec (and elsewhere).
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*/
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void vhdx_guid_generate(MSGUID *guid)
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{
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uuid_t uuid;
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assert(guid != NULL);
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uuid_generate(uuid);
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memcpy(guid, uuid, sizeof(MSGUID));
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}
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/*
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* Per the MS VHDX Specification, for every VHDX file:
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* - The header section is fixed size - 1 MB
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@ -251,6 +294,113 @@ static void vhdx_header_le_import(VHDXHeader *h)
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le64_to_cpus(&h->log_offset);
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}
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/* All VHDX structures on disk are little endian */
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static void vhdx_header_le_export(VHDXHeader *orig_h, VHDXHeader *new_h)
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{
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assert(orig_h != NULL);
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assert(new_h != NULL);
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new_h->signature = cpu_to_le32(orig_h->signature);
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new_h->checksum = cpu_to_le32(orig_h->checksum);
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new_h->sequence_number = cpu_to_le64(orig_h->sequence_number);
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new_h->file_write_guid = orig_h->file_write_guid;
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new_h->data_write_guid = orig_h->data_write_guid;
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new_h->log_guid = orig_h->log_guid;
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cpu_to_leguids(&new_h->file_write_guid);
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cpu_to_leguids(&new_h->data_write_guid);
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cpu_to_leguids(&new_h->log_guid);
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new_h->log_version = cpu_to_le16(orig_h->log_version);
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new_h->version = cpu_to_le16(orig_h->version);
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new_h->log_length = cpu_to_le32(orig_h->log_length);
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new_h->log_offset = cpu_to_le64(orig_h->log_offset);
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}
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/* Update the VHDX headers
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*
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* This follows the VHDX spec procedures for header updates.
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*
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* - non-current header is updated with largest sequence number
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*/
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static int vhdx_update_header(BlockDriverState *bs, BDRVVHDXState *s,
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bool generate_data_write_guid)
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{
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int ret = 0;
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int hdr_idx = 0;
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uint64_t header_offset = VHDX_HEADER1_OFFSET;
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VHDXHeader *active_header;
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VHDXHeader *inactive_header;
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VHDXHeader header_le;
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uint8_t *buffer;
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/* operate on the non-current header */
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if (s->curr_header == 0) {
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hdr_idx = 1;
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header_offset = VHDX_HEADER2_OFFSET;
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}
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active_header = s->headers[s->curr_header];
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inactive_header = s->headers[hdr_idx];
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inactive_header->sequence_number = active_header->sequence_number + 1;
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/* a new file guid must be generated before any file write, including
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* headers */
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inactive_header->file_write_guid = s->session_guid;
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/* a new data guid only needs to be generated before any guest-visible
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* writes (i.e. something observable via virtual disk read) */
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if (generate_data_write_guid) {
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vhdx_guid_generate(&inactive_header->data_write_guid);
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}
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/* the header checksum is not over just the packed size of VHDXHeader,
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* but rather over the entire 'reserved' range for the header, which is
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* 4KB (VHDX_HEADER_SIZE). */
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buffer = qemu_blockalign(bs, VHDX_HEADER_SIZE);
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/* we can't assume the extra reserved bytes are 0 */
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ret = bdrv_pread(bs->file, header_offset, buffer, VHDX_HEADER_SIZE);
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if (ret < 0) {
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goto exit;
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}
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/* overwrite the actual VHDXHeader portion */
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memcpy(buffer, inactive_header, sizeof(VHDXHeader));
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inactive_header->checksum =
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vhdx_update_checksum(buffer, VHDX_HEADER_SIZE,
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offsetof(VHDXHeader, checksum));
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vhdx_header_le_export(inactive_header, &header_le);
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ret = bdrv_pwrite_sync(bs->file, header_offset, &header_le,
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sizeof(VHDXHeader));
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if (ret < 0) {
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goto exit;
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}
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s->curr_header = hdr_idx;
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exit:
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qemu_vfree(buffer);
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return ret;
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}
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/*
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* The VHDX spec calls for header updates to be performed twice, so that both
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* the current and non-current header have valid info
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*/
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static int vhdx_update_headers(BlockDriverState *bs, BDRVVHDXState *s,
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bool generate_data_write_guid)
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{
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int ret;
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ret = vhdx_update_header(bs, s, generate_data_write_guid);
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if (ret < 0) {
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return ret;
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}
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ret = vhdx_update_header(bs, s, generate_data_write_guid);
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return ret;
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}
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/* opens the specified header block from the VHDX file header section */
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static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
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@ -742,6 +892,11 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
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goto fail;
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}
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/* This is used for any header updates, for the file_write_guid.
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* The spec dictates that a new value should be used for the first
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* header update */
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vhdx_guid_generate(&s->session_guid);
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ret = vhdx_parse_header(bs, s);
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if (ret) {
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goto fail;
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@ -804,8 +959,10 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
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}
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if (flags & BDRV_O_RDWR) {
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ret = -ENOTSUP;
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goto fail;
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ret = vhdx_update_headers(bs, s, false);
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if (ret < 0) {
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goto fail;
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}
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}
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/* TODO: differencing files, write */
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