[v2,2/6] blockdev: Allow overriding if_max_dev property

The if_max_devs table as in the past been an immutable
default that controls the mapping of index => (bus,unit)
for all boards and all HBAs for each interface type.

Since adding this mapping information to the HBA device
itself is currently unwieldly from the perspective of
retrieving this information at option parsing time
(e.g, within drive_new), we consider the alternative
of marking the if_max_devs table mutable so that
later configuration and initialization can adjust the
mapping at will, but only up until a drive is added,
at which point the mapping is finalized.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 blockdev.c                | 26 +++++++++++++++++++++++++-
 include/sysemu/blockdev.h |  2 ++
 2 files changed, 27 insertions(+), 1 deletion(-)

John Snow <jsnow@redhat.com> writes:

> The if_max_devs table as in the past been an immutable
> default that controls the mapping of index => (bus,unit)
> for all boards and all HBAs for each interface type.
>
> Since adding this mapping information to the HBA device
> itself is currently unwieldly from the perspective of
> retrieving this information at option parsing time
> (e.g, within drive_new), we consider the alternative
> of marking the if_max_devs table mutable so that
> later configuration and initialization can adjust the
> mapping at will, but only up until a drive is added,
> at which point the mapping is finalized.
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  blockdev.c                | 26 +++++++++++++++++++++++++-
>  include/sysemu/blockdev.h |  2 ++
>  2 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/blockdev.c b/blockdev.c
> index 81398e7..9b05f1b 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -60,7 +60,7 @@ static const char *const if_name[IF_COUNT] = {
>      [IF_XEN] = "xen",
>  };
>  
> -static const int if_max_devs[IF_COUNT] = {
> +static int if_max_devs[IF_COUNT] = {
>      /*
>       * Do not change these numbers!  They govern how drive option
>       * index maps to unit and bus.  That mapping is ABI.
> @@ -79,6 +79,30 @@ static const int if_max_devs[IF_COUNT] = {
>      [IF_SCSI] = 7,
>  };
>  
> +/**
> + * Boards may call this to offer board-by-board overrides
> + * of the default, global values.
> + */
> +void override_max_devs(BlockInterfaceType type, int max_devs)
> +{
> +    DriveInfo *dinfo;
> +
> +    if (max_devs <= 0) {
> +        return;
> +    }
> +
> +    QTAILQ_FOREACH(dinfo, &drives, next) {
> +        if (dinfo->type == type) {
> +            fprintf(stderr, "Cannot override units-per-bus property of"
> +                    " the %s interface, because a drive of that type has"
> +                    " already been added.\n", if_name[type]);
> +            g_assert_not_reached();
> +        }

I'd prefer a straightforward

    QTAILQ_FOREACH(dinfo, &drives, next) {
        assert(dinfo->type != type);
    }

or even

    assert(QTAILQ_EMPTY(drives));

assuming it actually holds.

> +    }
> +
> +    if_max_devs[type] = max_devs;
> +}
> +
>  /*
>   * We automatically delete the drive when a device using it gets
>   * unplugged.  Questionable feature, but we can't just drop it.
> diff --git a/include/sysemu/blockdev.h b/include/sysemu/blockdev.h
> index 80f768d..f23d495 100644
> --- a/include/sysemu/blockdev.h
> +++ b/include/sysemu/blockdev.h
> @@ -46,6 +46,8 @@ struct DriveInfo {
>      QTAILQ_ENTRY(DriveInfo) next;
>  };
>  
> +void override_max_devs(BlockInterfaceType type, int max_devs);
> +
>  DriveInfo *drive_get(BlockInterfaceType type, int bus, int unit);
>  bool drive_check_orphaned(void);
>  DriveInfo *drive_get_by_index(BlockInterfaceType type, int index);