Bug 315236 – Content rule list store may end up copying compiled bytecode files

• Status: ASSIGNED
• Component: WebKit Misc.

[Adrian Perez]

When compiling a JSON rule list, the flow is roughly:

  1. Calculate the destination location for the compiled file.
  2. Create a temporary file, using WTF::openTemporaryFile().
  3. Write compiled bytecode to the temporary file.
  4. Delete the destination file (if exists).
  5. Use WTF::moveFile() to “rename” the temporary file in the final location.

The issue here is that (2.) uses a platform-dependent temporary directory for
created temporary files, and for some ports it can easily end up being in a file
system different than the final destination, resulting in WTF::moveFile() falling
back to a *synchronous* copy.

Case example: the GTK and WPE ports use g_get_tmp_dir() for the temporary
file location, which most of the time will be /tmp. On modern Linux distributions
and embedded devices this can very easily be in-memory (tmpfs), and/or the
user's home directory (where programs will configure the ContentRuleListStore
data directory) may be on its own volume.

[Adrian Perez]

Pull request: https://github.com/WebKit/WebKit/pull/65336