SQLite: add preliminary support for Virtual File Systems

[dsshep]

SQLite has a feature, Virtual File Systems, which allows more control over how SQLite interacts with the OS.

At the moment it is possible to register and use a vfs with Microsoft.Data.Sqlite. The native bindings that SqliteConnection relies on, SqlitePclRaw, has the methods (although not directly exposed) for registering, listing and unregistering a vfs.

However, managing which vfs a SqliteConnection is associated with is not currently possible. If you want a different vfs to be used, you must make it the default and therefore all connections will use it.

For now, if there was a way of passing the vfs name when the connection is being opened (e.g. in the connection string), it would be possible to open connections and pool them with a different vfs. The (involved) process of actually creating the vfs can be left up to the reader...

This had previously been suggested (#21797) and closed as no justification was given for it. There has also been some API discussion: #27986 (comment). I have also implemented a more up to date version of this in a fork https://github.com/dsshep/efcore/tree/sqlite-vfs.

[ajcvickers]

/cc @bricelam

[bricelam]

if there was a way of passing the vfs name when the connection is being opened (e.g. in the connection string)

This is possible today.

var connection = new SqliteConnection("Data Source=\"file:Example.db?vfs=my-vfs\"");
connection.Open();

[dsshep]

Huh, was not aware that it would pass through. Thank you for the quick reply!