Re: [Qemu-devel] [PATCH v2 3/5] block: initial VHDX driver support framework - supports open and probe

[Jeff Cody]

On Sun, Apr 28, 2013 at 05:58:55PM +0800, Fam Zheng wrote:
> On Tue, 04/23 10:24, Jeff Cody wrote:
> > +/* opens the specified header block from the VHDX file header section */
> > +static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
> > +{
> > +    int ret = 0;
> > +    vhdx_header *header1;
> > +    vhdx_header *header2;
> > +    uint64_t h1_seq = 0;
> > +    uint64_t h2_seq = 0;
> > +    uint8_t *buffer;
> > +
> > +    header1 = qemu_blockalign(bs, sizeof(vhdx_header));
> > +    header2 = qemu_blockalign(bs, sizeof(vhdx_header));
> > +
> > +    buffer = qemu_blockalign(bs, VHDX_HEADER_SIZE);
> > +
> > +    s->headers[0] = header1;
> > +    s->headers[1] = header2;
> > +
> Logic for header1 and header2 are completely the same, IMO it might be
> better to avoid code with a loop.

> > +    /* We have to read the whole VHDX_HEADER_SIZE instead of
> > +     * sizeof(vhdx_header), because the checksum is over the whole
> > +     * region */
> > +    ret = bdrv_pread(bs->file, VHDX_HEADER1_OFFSET, buffer, 
> > VHDX_HEADER_SIZE);
> > +    if (ret < 0) {
> > +        goto fail;
> > +    }
> > +    /* copy over just the relevant portion that we need */
> > +    memcpy(header1, buffer, sizeof(vhdx_header));
> > +    vhdx_header_le_import(header1);
> > +
> > +    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
> > +        header1->signature == VHDX_HDR_MAGIC) {
> > +        h1_seq = header1->sequence_number;
> > +    }
> Do we need to check the version here? As the specification page 15 says:
> 
>     The Version field specifies the version of the VHDX format used
>     within the VHDX file. This field must be set to 1. If it is not, a
>     parser must not attempt to parse the file using the details from
>     this format specification.
> 

Yes, you are correct - I will add that in for v3.

> > +
> > +    ret = bdrv_pread(bs->file, VHDX_HEADER2_OFFSET, buffer, 
> > VHDX_HEADER_SIZE);
> > +    if (ret < 0) {
> > +        goto fail;
> > +    }
> > +    /* copy over just the relevant portion that we need */
> > +    memcpy(header2, buffer, sizeof(vhdx_header));
> > +    vhdx_header_le_import(header2);
> > +
> > +    if (vhdx_checksum_is_valid(buffer, VHDX_HEADER_SIZE, 4) &&
> > +        header2->signature == VHDX_HDR_MAGIC) {
> > +        h2_seq = header2->sequence_number;
> > +    }
> Same as above.
> > +
> > +    if (h1_seq > h2_seq) {
> > +        s->curr_header = 0;
> > +    } else if (h2_seq > h1_seq) {
> > +        s->curr_header = 1;
> > +    } else {
> > +        printf("NO VALID HEADER\n");
> > +        ret = -EINVAL;
> > +        goto fail;
> > +    }
> > +
> > +    ret = 0;
> > +
> > +    goto exit;
> > +
> > +fail:
> > +    qemu_vfree(header1);
> > +    qemu_vfree(header2);
> > +    s->headers[0] = NULL;
> > +    s->headers[1] = NULL;
> > +exit:
> > +    qemu_vfree(buffer);
> > +    return ret;
> > +}
> 
> -- 
> Fam