Mesa (main): util/fossilize_db: Be conservative about header length check for locking.

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Module: Mesa
Branch: main
Commit: 96bfefe8d1209b6aaa56fd77ca570789d82efb6e
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=96bfefe8d1209b6aaa56fd77ca570789d82efb6e

Author: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
Date:   Thu Aug  5 01:30:25 2021 +0200

util/fossilize_db: Be conservative about header length check for locking.

Don't anticipate seeing any partial written headers but just in case we
should probably wait on the lock to make sure whatever header was being
written is finished being written.

Fixes: 4f0f8133a35 "util/fossilize_db: Do not lock the fossilize db permanently."
Reviewed-by: Timothy Arceri <tarceri at itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12204>

---

 src/util/fossilize_db.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/util/fossilize_db.c b/src/util/fossilize_db.c
index af5c6e58581..46217f8a597 100644
--- a/src/util/fossilize_db.c
+++ b/src/util/fossilize_db.c
@@ -203,8 +203,9 @@ load_foz_dbs(struct foz_db *foz_db, FILE *db_idx, uint8_t file_idx,
    size_t len = ftell(db_idx);
    rewind(db_idx);
 
-   /* Try not to take the lock if len > 0, but if it is 0 we take the lock to initialize the files. */
-   if (len == 0) {
+   /* Try not to take the lock if len >= the size of the header, but if it is smaller we take the
+    * lock to potentially initialize the files. */
+   if (len < sizeof(stream_reference_magic_and_version)) {
       /* Wait for 100 ms in case of contention, after that we prioritize getting the app started. */
       int err = lock_file_with_timeout(foz_db->file[file_idx], 100000000);
       if (err == -1)