Re: [Qemu-devel] [PATCH v2 3/6] geometry: Add driver methods to probe blocksizes and geometry

[Markus Armbruster <armbru@redhat.com>]

Ekaterina Tumanova <tumanova@linux.vnet.ibm.com> writes:

> This patch introduces driver methods of defining disk blocksizes
> (physical and logical) and hard drive geometry.
> The method is only implemented for "host_device". For "raw" devices
> driver calls child's method.
> The detection will only work for DASD devices. In order to check that
> a local CheckForDASD function was introduced, which calls BIODASDINFO2 ioctl
> and returns 0 only if it succeeds.
>
> Signed-off-by: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
> ---
>  block/raw-posix.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  block/raw_bsd.c   | 12 ++++++++++
>  2 files changed, 77 insertions(+)
>
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 45f1d79..274ceda 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -56,6 +56,7 @@
>  #include <linux/cdrom.h>
>  #include <linux/fd.h>
>  #include <linux/fs.h>
> +#include <linux/hdreg.h>
>  #ifndef FS_NOCOW_FL
>  #define FS_NOCOW_FL                     0x00800000 /* Do not cow file */
>  #endif
> @@ -93,6 +94,10 @@
>  #include <xfs/xfs.h>
>  #endif
>  
> +#ifdef __s390__
> +#include <asm/dasd.h>
> +#endif
> +
>  //#define DEBUG_FLOPPY
>  
>  //#define DEBUG_BLOCK
> @@ -678,6 +683,64 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
>      bs->bl.opt_mem_alignment = s->buf_align;
>  }
>  
> +static int CheckForDASD(int fd)

As Christian said, no CamelCase for functions.

I guess your function returns either 0 or -1.  Can't say for sure
without looking up BIODASDINFO2.

I'd do a slightly higher level is_dasd() returning bool.  Your choice.

> +{
> +#ifdef BIODASDINFO2
> +    struct dasd_information2_t info = {0};
> +
> +    return ioctl(fd, BIODASDINFO2, &info);
> +#endif
> +    return -1;
> +}
> +
> +static struct ProbeBlockSize hdev_probe_blocksizes(BlockDriverState *bs)
> +{
> +    BDRVRawState *s = bs->opaque;
> +    struct ProbeBlockSize block_sizes = {0};
> +
> +    block_sizes.rc = CheckForDASD(s->fd);
> +    /* If DASD, get blocksizes */
> +    if (block_sizes.rc == 0) {
> +        block_sizes.size.log = probe_logical_blocksize(bs, s->fd);
> +        block_sizes.size.phys = probe_physical_blocksize(bs, s->fd);
> +    }
> +
> +    return block_sizes;
> +}

Fails unless DASD.  Why?  The block size concept applies not just to
DASD, and the probe_*_blocksize() functions should just work, shouldn't
they?

> +
> +static struct ProbeGeometry hdev_probe_geometry(BlockDriverState *bs)
> +{
> +    BDRVRawState *s = bs->opaque;
> +    struct ProbeGeometry geometry = {0};
> +    struct hd_geometry ioctl_geo = {0};

Is this initializer really necessary?

Because I like my local variable names short & sweet, I'd call this one
geo.  Your choice.

> +
> +    geometry.rc = CheckForDASD(s->fd);
> +    if (geometry.rc != 0) {

Works if your function really returns either 0 or -1.  If it can return
a positive value, it breaks the callback's contract.

> +        goto done;
> +    }
> +    /* If DASD, get it's geometry */

its

> +    geometry.rc = ioctl(s->fd, HDIO_GETGEO, &ioctl_geo);
> +    /* Do not return a geometry for partition */
> +    if (ioctl_geo.start != 0) {
> +        geometry.rc = -1;
> +        goto done;
> +    }
> +    /* HDIO_GETGEO may return success even though geo contains zeros
> +       (e.g. certain multipath setups) */
> +    if (!ioctl_geo.heads || !ioctl_geo.sectors || !ioctl_geo.cylinders) {
> +        geometry.rc = -1;
> +        goto done;
> +    }
> +    if (geometry.rc == 0) {
> +        geometry.geo.heads = (uint32_t)ioctl_geo.heads;
> +        geometry.geo.sectors = (uint32_t)ioctl_geo.sectors;
> +        geometry.geo.cylinders = (uint32_t)ioctl_geo.cylinders;

The LHS is uint32_t, the RHS is unsigned char or unsigned short, thus
the type casts are superfluous clutter.

8-bit head * 8-bit sectors * 16-bit cylinders can't represent today's
disk sizes, so ioctl_geo.cylinders is generally useless.  The common
advice is to ignore it, and do something like

    geometry.geo.cylinders = nb_sectors / (ioctl_geo.heads * ioctl_geo.sectors)

A possible alternative is to explicitly document that the returned
cylinders value can't be trusted.

Another one is not to return the number of cylinders :)

> +        geometry.geo.start = (uint32_t)ioctl_geo.start;

Always assigns zero (we checked above).  Why is member geo_start useful?

> +    }
> +done:
> +   return geometry;
> +}

Also fails unless DASD.  The geometry concept applies pretty much only
to disks older than thirty years or so, and to software designed for
them, like HDIO_GETGEO.

> +
>  static ssize_t handle_aiocb_ioctl(RawPosixAIOData *aiocb)
>  {
>      int ret;
> @@ -2128,6 +2191,8 @@ static BlockDriver bdrv_host_device = {
>      .bdrv_get_info = raw_get_info,
>      .bdrv_get_allocated_file_size
>                          = raw_get_allocated_file_size,
> +    .bdrv_probe_blocksizes = hdev_probe_blocksizes,
> +    .bdrv_probe_geometry = hdev_probe_geometry,
>  
>      .bdrv_detach_aio_context = raw_detach_aio_context,
>      .bdrv_attach_aio_context = raw_attach_aio_context,
> diff --git a/block/raw_bsd.c b/block/raw_bsd.c
> index 401b967..d164eba 100644
> --- a/block/raw_bsd.c
> +++ b/block/raw_bsd.c
> @@ -173,6 +173,16 @@ static int raw_probe(const uint8_t *buf, int buf_size, const char *filename)
>      return 1;
>  }
>  
> +static struct ProbeBlockSize raw_probe_blocksizes(BlockDriverState *bs)
> +{
> +    return bdrv_probe_blocksizes(bs->file);
> +}
> +
> +static struct ProbeGeometry raw_probe_geometry(BlockDriverState *bs)
> +{
> +    return bdrv_probe_geometry(bs->file);
> +}
> +
>  static BlockDriver bdrv_raw = {
>      .format_name          = "raw",
>      .bdrv_probe           = &raw_probe,
> @@ -190,6 +200,8 @@ static BlockDriver bdrv_raw = {
>      .has_variable_length  = true,
>      .bdrv_get_info        = &raw_get_info,
>      .bdrv_refresh_limits  = &raw_refresh_limits,
> +    .bdrv_probe_blocksizes = &raw_probe_blocksizes,
> +    .bdrv_probe_geometry  = &raw_probe_geometry,
>      .bdrv_is_inserted     = &raw_is_inserted,
>      .bdrv_media_changed   = &raw_media_changed,
>      .bdrv_eject           = &raw_eject,