On 01/22/2016 03:51 PM, John Snow wrote:
> This one is the crazy one.
>
> fd_revalidate currently uses pick_geometry to tell if the diskette
> geometry has changed upon an eject/insert event, but it won't allow us
> to insert a 1.44MB diskette into a 2.88MB drive. This is inflexible.
>
> The new algorithm applies a new heuristic to guessing disk geometries
> that allows us to switch diskette types as long as the physical size
> matches before falling back to the old heuristic.
>
> The old one is roughly:
> - If the size (sectors) and type matches, choose it.
> - Fall back to the first geometry that matched our type.
>
> The new one is:
> - If the size (sectors) and type matches, choose it.
> - If the size (sectors) and physical size match, choose it.
> - If the size (sectors) matches at all, choose it begrudgingly.
> - Fall back to the first geometry that matched our type.
>
Goofed and didn't update commit. Will change on PULL to omit the third
line if the patch is otherwise OK.
> Signed-off-by: John Snow <js...@redhat.com>
> ---
> hw/block/fdc.c | 72
> ++++++++++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 52 insertions(+), 20 deletions(-)
>
> diff --git a/hw/block/fdc.c b/hw/block/fdc.c
> index e51154b..6e0c5fc 100644
> --- a/hw/block/fdc.c
> +++ b/hw/block/fdc.c
> @@ -125,7 +125,6 @@ static const FDFormat fd_formats[] = {
> { FLOPPY_DRIVE_TYPE_NONE, -1, -1, 0, 0, },
> };
>
> -__attribute__((__unused__))
> static FDriveSize drive_size(FloppyDriveType drive)
> {
> switch (drive) {
> @@ -284,45 +283,78 @@ static int pick_geometry(FDrive *drv)
> BlockBackend *blk = drv->blk;
> const FDFormat *parse;
> uint64_t nb_sectors, size;
> - int i, first_match, match;
> + int i;
> + int match, size_match, type_match;
> + bool magic = drv->drive == FLOPPY_DRIVE_TYPE_AUTO;
>
> /* We can only pick a geometry if we have a diskette. */
> if (!drv->media_inserted || drv->drive == FLOPPY_DRIVE_TYPE_NONE) {
> return -1;
> }
>
> + /* We need to determine the likely geometry of the inserted medium.
> + * In order of preference, we look for:
> + * (1) The same drive type and number of sectors,
> + * (2) The same diskette size and number of sectors,
> + * (3) The same drive type.
> + *
> + * In all cases, matches that occur higher in the drive table will take
> + * precedence over matches that occur later in the table.
> + */
> blk_get_geometry(blk, &nb_sectors);
> - match = -1;
> - first_match = -1;
> + match = size_match = type_match = -1;
> for (i = 0; ; i++) {
> parse = &fd_formats[i];
> if (parse->drive == FLOPPY_DRIVE_TYPE_NONE) {
> break;
> }
> - if (drv->drive == parse->drive ||
> - drv->drive == FLOPPY_DRIVE_TYPE_AUTO) {
> - size = (parse->max_head + 1) * parse->max_track *
> - parse->last_sect;
> - if (nb_sectors == size) {
> - match = i;
> - break;
> + size = (parse->max_head + 1) * parse->max_track * parse->last_sect;
> + if (nb_sectors == size) {
> + if (magic || parse->drive == drv->drive) {
> + /* (1) perfect match -- nb_sectors and drive type */
> + goto out;
> + } else if (drive_size(parse->drive) == drive_size(drv->drive)) {
> + /* (2) size match -- nb_sectors and physical medium size */
> + match = (match == -1) ? i : match;
> + } else {
> + /* This is suspicious -- Did the user misconfigure? */
> + size_match = (size_match == -1) ? i : size_match;
> }
> - if (first_match == -1) {
> - first_match = i;
> + } else if (type_match == -1) {
> + if ((parse->drive == drv->drive) ||
> + (magic && (parse->drive == get_fallback_drive_type(drv)))) {
> + /* (3) type match -- nb_sectors mismatch, but matches the
> type
> + * specified explicitly by the user, or matches the
> fallback
> + * default type when using the drive autodetect
> mechanism */
> + type_match = i;
> }
> }
> }
> +
> + /* No exact match found */
> if (match == -1) {
> - if (first_match == -1) {
> - error_setg(&error_abort, "No candidate geometries present in
> table "
> - " for floppy drive type '%s'",
> - FloppyDriveType_lookup[drv->drive]);
> - } else {
> - match = first_match;
> + if (size_match != -1) {
> + parse = &fd_formats[size_match];
> + FLOPPY_DPRINTF("User requested floppy drive type '%s', "
> + "but inserted medium appears to be a "
> + "%d sector '%s' type\n",
> + FloppyDriveType_lookup[drv->drive],
> + nb_sectors,
> + FloppyDriveType_lookup[parse->drive]);
> }
> - parse = &fd_formats[match];
> + match = type_match;
> }
>
> + /* No match of any kind found -- fd_format is misconfigured, abort. */
> + if (match == -1) {
> + error_setg(&error_abort, "No candidate geometries present in table "
> + " for floppy drive type '%s'",
> + FloppyDriveType_lookup[drv->drive]);
> + }
> +
> + parse = &(fd_formats[match]);
> +
> + out:
> if (parse->max_head == 0) {
> drv->flags &= ~FDISK_DBL_SIDES;
> } else {
>
--
—js
