CHROMIUM: unroll the outer for-loop of VbExDiskGetInfo()

VbExDiskGetInfo() was implemented with nested loops, where the outer
loop iterates iterators, and the inner loop runs through block devices
via the iterator.

It was quite complicated and the outer loop only iterates twice. So we
believe it will make the code more readable if we unroll the outer
for-loop.

Besides unrolling the loop, we fix a logic error that disk_flags should
be tested 'is subset of' rather than 'has non-empty intersection with'
flags.

BUG=chromium-os:16542
TEST=vbexport_test diskinfo

Change-Id: Ic4a7d516d91ba7214b9b67eebbecf02f80b11786
Signed-off-by: Tammo Spalink <tammo@chromium.org>
Reviewed-on: http://gerrit.chromium.org/gerrit/4472
Tested-by: Che-Liang Chiou <clchiou@chromium.org>
Reviewed-by: Tom Wai-Hong Tam <waihong@chromium.org>

1 files changed, 49 insertions, 37 deletions

diff --git a/lib/vbexport/boot_device.c b/lib/vbexport/boot_device.c
index 059c521c0f..bd378e5b8f 100644
--- a/lib/vbexport/boot_device.c
+++ b/lib/vbexport/boot_device.c
@@ -67,8 +67,6 @@ static void init_usb_storage(void)
 		usb_stor_scan(/*mode=*/1);
 }
 
-typedef block_dev_desc_t *(device_iterator_func)(int *);
-
 block_dev_desc_t *iterate_mmc_device(int *index_ptr)
 {
 	struct mmc *mmc;
@@ -95,54 +93,68 @@ block_dev_desc_t *iterate_usb_device(int *index_ptr)
 	return usb_stor_get_dev((*index_ptr)++);
 }
 
+/*
+ * This appends [dev] to [info] and increments [count_ptr] if [disk_flags] is a
+ * subset of the flags of [dev].
+ */
+void add_device_if_flags_match(block_dev_desc_t *dev, const uint32_t disk_flags,
+		VbDiskInfo *info, uint32_t *count_ptr)
+{
+	uint32_t flags = get_dev_flags(dev);
+
+	/*
+	 * Only add this storage device if the properties of disk_flags is a
+	 * subset of the properties of flags.
+	 */
+	if ((flags & disk_flags) != disk_flags)
+		return;
+
+	info->handle = (VbExDiskHandle_t)dev;
+	info->bytes_per_lba = dev->blksz;
+	info->lba_count = dev->lba;
+	info->flags = flags;
+	info->name = get_dev_name(dev);
+	(*count_ptr)++;
+}
+
 VbError_t VbExDiskGetInfo(VbDiskInfo** infos_ptr, uint32_t* count_ptr,
                           uint32_t disk_flags)
 {
-	device_iterator_func *iterators[] = {
-		iterate_mmc_device, iterate_usb_device, NULL
-	};
-	device_iterator_func *iter;
 	VbDiskInfo *infos;
+	uint32_t count, max_count;
+	int iterator_state;
 	block_dev_desc_t *dev;
-	uint32_t count, max_count, flags;
-	int i, func_index;
 
 	*infos_ptr = NULL;
 	*count_ptr = 0;
 
-	/* We assume there is only one non-removable storage device */
+	/* We return as many disk infos as possible. */
+	/*
+	 * We assume there is only one non-removable storage device. So if the
+	 * caller asks for non-removable devices, we return at most one device.
+	 * Otherwise we return at most MAX_DISK_INFO device.
+	 */
 	max_count = (disk_flags & VB_DISK_FLAG_REMOVABLE) ? MAX_DISK_INFO : 1;
+
+	/* count is the number of device returned */
 	infos = (VbDiskInfo *)VbExMalloc(sizeof(VbDiskInfo) * max_count);
 	count = 0;
 
-	/* To speed up, skip detecting USB if not require removable devices. */
-	if (!(disk_flags & VB_DISK_FLAG_REMOVABLE))
-		iterators[1] = NULL;
-
-	/*
-	 * If too many storage devices registered, we return as many disk infos
-	 * as possible.
-	 */
-	for (func_index = 0;
-	     count < max_count && (iter = iterators[func_index]);
-	     func_index++) {
-		if (iter == iterate_usb_device)
-			init_usb_storage();
-
-		i = 0;
-		while (count < max_count && (dev = iter(&i))) {
-			/* Skip this entry if the flags are not matched. */
-			flags = get_dev_flags(dev);
-			if (!(flags & disk_flags))
-				continue;
-
-			infos[count].handle = (VbExDiskHandle_t)dev;
-			infos[count].bytes_per_lba = dev->blksz;
-			infos[count].lba_count = dev->lba;
-			infos[count].flags = flags;
-			infos[count].name = get_dev_name(dev);
-			count++;
-		}
+	iterator_state = 0;
+	while (count < max_count && (dev = iterate_mmc_device(&iterator_state)))
+		add_device_if_flags_match(dev, disk_flags,
+				infos + count, &count);
+
+	/* Skip probing USB device if not require removable devices. */
+        if (count < max_count && (disk_flags & VB_DISK_FLAG_REMOVABLE)) {
+		/* Initialize USB device before probing them. */
+		init_usb_storage();
+
+		iterator_state = 0;
+		while (count < max_count &&
+				(dev = iterate_usb_device(&iterator_state)))
+			add_device_if_flags_match(dev, disk_flags,
+					infos + count, &count);
 	}
 
 	if (count) {