cgpt: Rework number of entries calculation
As pointed out by Daniel in CL:234996, the half_size_sectors should have
been checked in both places.
This CL reworks that part of the code to read easier.
BUG=none
BRANCH=none
TEST=unittest
Change-Id: I8faea3b094c375e4fd1a604a8fe759af88943fdf
Reviewed-on: https://chromium-review.googlesource.com/235792
Reviewed-by: Daniel Ehrenberg <dehrenberg@chromium.org>
Tested-by: Nam Nguyen <namnguyen@chromium.org>
Commit-Queue: Nam Nguyen <namnguyen@chromium.org>
diff --git a/cgpt/cgpt_create.c b/cgpt/cgpt_create.c
index 64f3f4d..60e23c9 100644
--- a/cgpt/cgpt_create.c
+++ b/cgpt/cgpt_create.c
@@ -51,19 +51,29 @@
h->number_of_entries = TOTAL_ENTRIES_SIZE / h->size_of_entry;
if (drive->gpt.flags & GPT_FLAG_EXTERNAL) {
// We might have smaller space for the GPT table. Scale accordingly.
- size_t half_size_sectors = drive->gpt.gpt_drive_sectors / 2;
- if (half_size_sectors < GPT_HEADER_SECTORS) {
- Error("Not enough space for a GPT header.\n");
+ //
+ // +------+------------+---------------+-----+--------------+-----------+
+ // | PMBR | Prim. Head | Prim. Entries | ... | Sec. Entries | Sec. Head |
+ // +------+------------+---------------+-----+--------------+-----------+
+ //
+ // Half the size of gpt_drive_sectors must be big enough to hold PMBR +
+ // GPT Header + Entries Table, though the secondary structures do not
+ // contain PMBR.
+ size_t required_headers_size =
+ (GPT_PMBR_SECTORS + GPT_HEADER_SECTORS) * drive->gpt.sector_bytes;
+ size_t min_entries_size = MIN_NUMBER_OF_ENTRIES * h->size_of_entry;
+ size_t required_min_size = required_headers_size + min_entries_size;
+ size_t half_size =
+ (drive->gpt.gpt_drive_sectors / 2) * drive->gpt.sector_bytes;
+ if (half_size < required_min_size) {
+ Error("Not enough space to store GPT structures. Required %d bytes.\n",
+ required_min_size * 2);
return -1;
}
- half_size_sectors -= (GPT_HEADER_SECTORS + GPT_PMBR_SECTORS);
- size_t half_size = half_size_sectors * drive->gpt.sector_bytes;
- if (half_size < (MIN_NUMBER_OF_ENTRIES * h->size_of_entry)) {
- Error("Not enough space for minimum number of entries.\n");
- return -1;
- }
- if (128 > (half_size / h->size_of_entry)) {
- h->number_of_entries = half_size / h->size_of_entry;
+ size_t max_entries =
+ (half_size - required_headers_size) / h->size_of_entry;
+ if (h->number_of_entries > max_entries) {
+ h->number_of_entries = max_entries;
}
}
diff --git a/tests/run_cgpt_tests.sh b/tests/run_cgpt_tests.sh
index 7170eef..5176017 100755
--- a/tests/run_cgpt_tests.sh
+++ b/tests/run_cgpt_tests.sh
@@ -291,6 +291,12 @@
# Enable write access again to test boundary in off device storage
chmod 600 ${DEV}
+# GPT too small
+dd if=/dev/zero of=${DEV} bs=5632 count=1
+assert_fail $CGPT create -D 1024 ${DEV}
+# GPT is just right for 16 entries (512 + 512 + 16 * 128) * 2 = 6144
+dd if=/dev/zero of=${DEV} bs=6144 count=1
+$CGPT create -D 1024 ${DEV}
# Create a small 8K file to simulate Flash NOR section
dd if=/dev/zero of=${DEV} bs=8K count=1
# Drive size is not multiple of 512