[PATCH 1/2] Clear the total block transfer count on error.

[Kevin O'Connor]

The total number of blocks transferred is part of the return status of
the BIOS API.  This is normally the total number of blocks requested.
However, in an error it is possible for this count to be less.  Add a
global check to ensure that on an error event the block count is
updated - if it hasn't been updated, assume that no blocks have been
transferred successfully (the common case).

Signed-off-by: Kevin O'Connor 
---
 src/block.c | 40 +++++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/src/block.c b/src/block.c
index 7493a5d..4fbf058 100644
--- a/src/block.c
+++ b/src/block.c
@@ -350,28 +350,37 @@ int
 process_op(struct disk_op_s *op)
 {
     ASSERT16();
+    int ret, origcount = op->count;
     u8 type = GET_GLOBALFLAT(op->drive_gf->type);
     switch (type) {
     case DTYPE_FLOPPY:
-        return process_floppy_op(op);
+        ret = process_floppy_op(op);
+        break;
     case DTYPE_ATA:
-        return process_ata_op(op);
+        ret = process_ata_op(op);
+        break;
     case DTYPE_RAMDISK:
-        return process_ramdisk_op(op);
+        ret = process_ramdisk_op(op);
+        break;
     case DTYPE_CDEMU:
-        return process_cdemu_op(op);
+        ret = process_cdemu_op(op);
+        break;
     case DTYPE_VIRTIO_BLK:
-        return process_virtio_blk_op(op);
+        ret = process_virtio_blk_op(op);
+        break;
     case DTYPE_AHCI: ;
         extern void _cfunc32flat_process_ahci_op(void);
-        return call32(_cfunc32flat_process_ahci_op
-                      , (u32)MAKE_FLATPTR(GET_SEG(SS), op), DISK_RET_EPARAM);
+        ret = call32(_cfunc32flat_process_ahci_op
+                     , (u32)MAKE_FLATPTR(GET_SEG(SS), op), DISK_RET_EPARAM);
+        break;
     case DTYPE_ATA_ATAPI:
-        return process_atapi_op(op);
+        ret = process_atapi_op(op);
+        break;
     case DTYPE_AHCI_ATAPI: ;
         extern void _cfunc32flat_process_atapi_op(void);
-        return call32(_cfunc32flat_process_atapi_op
-                      , (u32)MAKE_FLATPTR(GET_SEG(SS), op), DISK_RET_EPARAM);
+        ret = call32(_cfunc32flat_process_atapi_op
+                     , (u32)MAKE_FLATPTR(GET_SEG(SS), op), DISK_RET_EPARAM);
+        break;
     case DTYPE_USB:
     case DTYPE_UAS:
     case DTYPE_VIRTIO_SCSI:
@@ -379,11 +388,16 @@ process_op(struct disk_op_s *op)
     case DTYPE_ESP_SCSI:
     case DTYPE_MEGASAS:
     case DTYPE_PVSCSI:
-        return process_scsi_op(op);
+        ret = process_scsi_op(op);
+        break;
     default:
-        op->count = 0;
-        return DISK_RET_EPARAM;
+        ret = DISK_RET_EPARAM;
+        break;
     }
+    if (ret && op->count == origcount)
+        // If the count hasn't changed on error, assume no data transferred.
+        op->count = 0;
+    return ret;
 }

// Execute a "disk_op_s" request - this runs on the extra stack.