* mount: fail reads with error when chunk manifest resolution fails
When SetChunks fails to resolve a chunk manifest (e.g. the volume is on a
remote tier with reads disabled), the sections map stays empty and
readDataAtSequential/readDataAtParallel zero-fill every missing section as
if it were a sparse hole. Reads then return all-zero data with no error,
so a plain cp of a large manifest-based file silently produces a
completely zero-filled file.
Remember the resolve error in ChunkGroup (guarded by sectionsLock) and
return it from ReadDataAt. A later successful SetChunks clears it.
Fixes the mount path of #11286.
* filer: propagate manifest resolve errors in streaming read paths
ViewFromChunks discards the chunk manifest resolve error returned by
NonOverlappingVisibleIntervals. On failure the chunk views come back
empty, and the streaming paths zero-fill the entire requested range,
serving HTTP 200 / WebDAV 200 responses whose body is all zeros.
Propagate the error in PrepareStreamContentWithThrottler,
PrepareStreamContentWithPrefetch and the WebDAV read path so these
requests fail with 500 instead.
Fixes the filer HTTP and WebDAV paths of #11286.
* mount: fail lseek with EIO when chunk manifest resolution fails
SearchChunks still consulted the stale section map after SetChunks
recorded a manifest resolution failure, so SEEK_DATA/SEEK_HOLE would
describe the unresolved regions as sparse holes or return ENXIO.
Return the recorded error from SearchChunks and map it to EIO in
Lseek.
Also add regression tests for the stream preparation error paths.
Addresses review feedback on #11287.
Bruce Zou
eb6a7e93ca