* filer_pb,filer: per-mutation preconditions on ObjectTransaction
A transaction's request-level condition evaluates one entry before any
mutation runs, so a commit guarding two paths — the object it publishes
and the upload directory it assembles — could not be expressed. Give each
ObjectMutation an optional condition (evaluated against condition_key,
else the mutation's target, under the same lock just before the mutation
applies) and report which mutation failed through failed_mutation on the
response, so callers can tell a mutation guard's rejection apart from the
request-level precondition's.
* s3: evaluate multipart completion conditions under the object lock
CompleteMultipartUpload checked conditional headers gateway-side before
committing, and the routed commit transaction guarded only the upload
directory — nothing made If-None-Match: * atomic with the publish, so
concurrent conditional completions of the same absent key could all
report success.
The request's reducible write condition (If-None-Match/If-Match, star or
single strong ETag) now rides the commit as the transaction's request
condition on the owner filer: on the object path for unversioned buckets,
falling back to the .versions directory for suspended and enabled
versioning. The upload-exists guard moves onto the PUT mutation, keeping
its check-before-publish ordering. Conditions the reducer cannot express
stay on the distributed write lock, where check and commit already
serialize.
* filer,s3: resolve the latest version first for versioned conditional writes
* filer: keep directory entries holding content out of the absent-slot rule
* s3: keep a gateway-side upload-exists check for filers without mutation conditions
* filer: honor null-version-is-latest resolving prefer-alt conditions
* drop scratch multipart-race repro programs
* s3: note the write lock does not cover routed writes on non-reducible conditions
Chris Lu
2737315e9d