Zero blocks before BLKDISCARD

Due to observed BLKDISCARD flakiness, overwrite blocks that we want
to discard with zeros first to avoid later issues with dm-verity if
BLKDISCARD is not successful.

Bug: 20614277
Bug: 20881595
Change-Id: I4f6f2db39db990879ff10468c9db41606497bd6f
(cherry picked from commit a3c75e3ea60d61df93461f5c356befe825c429d2)

1 files changed, 17 insertions, 1 deletions

diff --git a/updater/blockimg.c b/updater/blockimg.c
index 7b8721d..e184800 100644
--- a/updater/blockimg.c
+++ b/updater/blockimg.c
@@ -1404,6 +1404,7 @@ pcdout:
 static int PerformCommandErase(CommandParameters* params) {
     char* range = NULL;
     int i;
+    int j;
     int rc = -1;
     RangeSet* tgt = NULL;
     struct stat st;
@@ -1430,7 +1431,7 @@ static int PerformCommandErase(CommandParameters* params) {
     range = strtok_r(NULL, " ", &params->cpos);
 
     if (range == NULL) {
-        fprintf(stderr, "missing target blocks for zero\n");
+        fprintf(stderr, "missing target blocks for erase\n");
         goto pceout;
     }
 
@@ -1439,7 +1440,22 @@ static int PerformCommandErase(CommandParameters* params) {
     if (params->canwrite) {
         fprintf(stderr, " erasing %d blocks\n", tgt->size);
 
+        allocate(BLOCKSIZE, &params->buffer, &params->bufsize);
+        memset(params->buffer, 0, BLOCKSIZE);
+
         for (i = 0; i < tgt->count; ++i) {
+            // Always zero the blocks first to work around possibly flaky BLKDISCARD
+            // Bug: 20881595
+            if (!check_lseek(params->fd, (off64_t) tgt->pos[i * 2] * BLOCKSIZE, SEEK_SET)) {
+                goto pceout;
+            }
+
+            for (j = tgt->pos[i * 2]; j < tgt->pos[i * 2 + 1]; ++j) {
+                if (write_all(params->fd, params->buffer, BLOCKSIZE) == -1) {
+                    goto pceout;
+                }
+            }
+
             // offset in bytes
             blocks[0] = tgt->pos[i * 2] * (uint64_t) BLOCKSIZE;
             // length in bytes