Repair DBs with trailing slash in name

[ajkr]

Problem:

• DB::SanitizeOptions strips trailing slash from wal_dir but not dbname
• We check whether wal_dir and dbname refer to the same directory using string equality: https://github.com/facebook/rocksdb/blob/master/db/repair.cc#L258
• Providing dbname with trailing slash causes default wal_dir to be misidentified as a separate directory.
• Then the repair tries to add all SST files to the VersionEdit twice (once for dbname dir, once for wal_dir) and fails with coredump.

Solution:

• Add a new Env function, AreFilesSame, which uses device and inode number to check whether files are the same. It's currently only implemented in PosixEnv.
• Migrate repair to use AreFilesSame to check whether dbname and wal_dir are same. If unsupported, falls back to string comparison.

Test Plan:

• RepairTest.DbNameContainsTrailingSlash is regression test for the coredump
• RepairTest.SeparateWalDir (an existing test) covers the case where wal_dir and dbname are deliberately different.
• Also ran the two above tests with Env::AreFilesSame that returns Status::Unsupported

[facebook-github-bot]

@ajkr has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[yiwu-arbug]

LGTM.

[facebook-github-bot]

@ajkr has updated the pull request.

[facebook-github-bot]

@ajkr has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.