commit 0f0c6fcd0d2f6f7d98f1de51616de274f277ede0
author Ben Keller <galbanum@google.com> Sat Apr 27 03:09:32 2024 +0000
committer CQ Bot <fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com> Sat Apr 27 03:09:32 2024 +0000
tree 0b35cf34ffa4509445fc82d8b26d97a5fbfc13fb
parent 55f4ba3ccfe681a9c3769830e2b2f80a14d211de

[pkg] Do not open blobs to check for presence

During resolves, after the meta.far is fetched, when checking to see
if a content blob or subpackage meta.far needs to be downloaded,
pkg-cache tries to open the blob. This is not correct, because on
c++blob READ connections to partially written blobs keep the blob
alive even after the writer closes its connection, which creates the
following race condition:

1. blob is partially written by a concurrent resolve
2. blob is opened to check for presence
3. concurrent resolve hits an error and retries the fetch, which
   attempts to open the blob for write, which fails

Local Storage has said that ReadDirents on /blob for both c++blob and
fxblob is guaranteed to return blobs if and only if they are fully
written and do not have outstanding deletion requests, this CL removes
the open double check and relies only on ReadDirents to determine
which blobs are missing.

Fixed: 337104426
Change-Id: I20365520f8d4b01e26cce9a900db7ec9a2b93914
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1037588
Reviewed-by: Sen Jiang <senj@google.com>
Commit-Queue: Ben Keller <galbanum@google.com>