Re: [Qemu-devel] [PATCH v2 2/9] block: vhdx - add header update capability.

[Kevin Wolf <kwolf@redhat.com>]

Am 01.08.2013 um 05:23 hat Jeff Cody geschrieben:
> 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>
> ---
>  block/Makefile.objs |   2 +-
>  block/vhdx.c        | 157 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  block/vhdx.h        |  12 +++-
>  configure           |  13 +++++
>  4 files changed, 180 insertions(+), 4 deletions(-)
> 
> diff --git a/block/Makefile.objs b/block/Makefile.objs
> index 4cf9aa4..e5e54e6 100644
> --- a/block/Makefile.objs
> +++ b/block/Makefile.objs
> @@ -2,7 +2,7 @@ block-obj-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat
>  block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o qcow2-cache.o
>  block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
>  block-obj-y += qed-check.o
> -block-obj-y += vhdx.o
> +block-obj-$(CONFIG_VHDX) += vhdx.o
>  block-obj-y += parallels.o blkdebug.o blkverify.o
>  block-obj-y += snapshot.o qapi.o
>  block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
> diff --git a/block/vhdx.c b/block/vhdx.c
> index 56bc88e..9b50442 100644
> --- a/block/vhdx.c
> +++ b/block/vhdx.c
> @@ -21,6 +21,7 @@
>  #include "qemu/crc32c.h"
>  #include "block/vhdx.h"
>  
> +#include <uuid/uuid.h>
>  
>  /* Several metadata and region table data entries are identified by
>   * guids in  a MS-specific GUID format. */
> @@ -156,11 +157,40 @@ typedef struct BDRVVHDXState {
>      VHDXBatEntry *bat;
>      uint64_t bat_offset;
>  
> +    MSGUID session_guid;
> +
> +
>      VHDXParentLocatorHeader parent_header;
>      VHDXParentLocatorEntry *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)
> + *
> + * 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 + 4));

sizeof(crc) for consistency.

> +
> +    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)
>  {
> @@ -212,6 +242,24 @@ 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
> + *
> + */
> +void vhdx_guid_generate(MSGUID *guid)
> +{
> +    uuid_t uuid;
> +    assert(guid != NULL);
> +
> +    uuid_generate(uuid);
> +    memcpy(guid, uuid, 16);
> +}

Should MSGUID be QEMU_PACKED to make sure that this works? Also
sizeof(guid) instead of 16?

> +
> +/*
>   * 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"
> @@ -249,6 +297,107 @@ static void vhdx_header_le_import(VHDXHeader *h)
>      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);
> +
> +    memcpy(&new_h->file_write_guid, &orig_h->file_write_guid, sizeof(MSGUID));
> +    memcpy(&new_h->data_write_guid, &orig_h->data_write_guid, sizeof(MSGUID));
> +    memcpy(&new_h->log_guid,        &orig_h->log_guid,        sizeof(MSGUID));

Can we avoid memcpy? I think this should work:

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 rw)
> +{
> +    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 generate before any file write, including
> +     * headers */
> +    memcpy(&inactive_header->file_write_guid, &s->session_guid,
> +           sizeof(MSGUID));

Here a simple assignment should do as well.

> +
> +    /* a new data guid only needs to be generate before any guest-visible
> +     * 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 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, 4);
> +    vhdx_header_le_export(inactive_header, &header_le);
> +    bdrv_pwrite_sync(bs->file, header_offset, &header_le, sizeof(VHDXHeader));
> +    s->curr_header = hdr_idx;
> +
> +exit:
> +    qemu_vfree(buffer);
> +    return ret;
> +}

Kevin