[coreboot-gerrit] New patch to review for coreboot: vboot/vbnv_flash: Binary search to find last used entry
Martin Roth (martinroth@google.com)
gerrit at coreboot.org
Mon Sep 12 18:20:39 CEST 2016
Martin Roth (martinroth at google.com) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/16577
-gerrit
commit 77b85086f61deec1e48a557469730c3892955c50
Author: Randall Spangler <rspangler at chromium.org>
Date: Fri Aug 26 16:01:16 2016 -0700
vboot/vbnv_flash: Binary search to find last used entry
This improves the previous linear search to O(log n). No change in
storage format.
BUG=chromium:640656
BRANCH=none
TEST=Manual
(test empty)
flashrom -i RW_NVRAM -e
Reboot; device should boot normally.
(start using records)
crossystem kern_nv=0xaab0
crossystem recovery_request=1 && reboot
Device should go into recovery mode with reason 1
Reboot again; it should boot normally.
crossystem kern_nv (should still contain 0xaab0)
Repeat steps several times with request=2, 3, etc.
flashrom -i RW_NVRAM -r nvdata
Modify nvdata to copy the first record across all valid
records
flashrom -i RW_NVRAM -w nvdata
Reboot; device should boot normally.
Change-Id: Ieb97563ab92bd1d18a4f6a9e1d20157efe311fb4
Signed-off-by: Martin Roth <martinroth at chromium.org>
Original-Commit-Id: db9bb2d3927ad57270d7acfd42cf0652102993b1
Original-Change-Id: I1eb5fd9fa6b2ae56833f024bcd3c250147bcc7a1
Original-Signed-off-by: Randall Spangler <rspangler at chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/376928
Original-Reviewed-by: Julius Werner <jwerner at chromium.org>
---
src/vboot/vbnv_flash.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)
diff --git a/src/vboot/vbnv_flash.c b/src/vboot/vbnv_flash.c
index 81c4f08..dd128a9 100644
--- a/src/vboot/vbnv_flash.c
+++ b/src/vboot/vbnv_flash.c
@@ -65,6 +65,7 @@ static int init_vbnv(void)
struct region_device *rdev = &ctx->vbnv_dev;
uint8_t buf[BLOB_SIZE];
uint8_t empty_blob[BLOB_SIZE];
+ int used_below, empty_above;
int offset;
int i;
@@ -78,25 +79,30 @@ static int init_vbnv(void)
for (i = 0; i < BLOB_SIZE; i++)
empty_blob[i] = erase_value();
- offset = 0;
ctx->top_offset = region_device_sz(rdev) - BLOB_SIZE;
- /*
- * after the loop, offset is supposed to point the blob right before
- * the first empty blob, the last blob in the nvram if there is no
- * empty blob, or the base of the region if the nvram has never been
- * used.
- */
- for (i = 0; i <= ctx->top_offset; i += BLOB_SIZE) {
- if (rdev_readat(rdev, buf, i, BLOB_SIZE) < 0) {
+ /* Binary search for the border between used and empty */
+ used_below = 0;
+ empty_above = region_device_sz(rdev) / BLOB_SIZE;
+
+ while (used_below + 1 < empty_above) {
+ int guess = (used_below + empty_above) / 2;
+ if (rdev_readat(rdev, buf, guess * BLOB_SIZE, BLOB_SIZE) < 0) {
printk(BIOS_ERR, "failed to read nvdata\n");
return 1;
}
if (!memcmp(buf, empty_blob, BLOB_SIZE))
- break;
- offset = i;
+ empty_above = guess;
+ else
+ used_below = guess;
}
+ /*
+ * Offset points to the last non-empty blob. Or if all blobs are empty
+ * (nvram is totally erased), point to the first blob.
+ */
+ offset = used_below * BLOB_SIZE;
+
/* reread the nvdata and write it to the cache */
if (rdev_readat(rdev, ctx->cache, offset, BLOB_SIZE) < 0) {
printk(BIOS_ERR, "failed to read nvdata\n");
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