Support opening local store with database on read-only filesystem (#8356)

Previously it was not possible to open a local store when its database is on a read-only filesystem. Obviously a store on a read-only filesystem cannot be modified, but it would still be useful to be able to query it.

This change adds a new read-only setting to LocalStore. When set to true, Nix will skip operations that fail when the database is on a read-only filesystem (acquiring big-lock, schema migration, etc), and the store database will be opened in immutable mode.

Co-authored-by: Ben Radford <benradf@users.noreply.github.com>
Co-authored-by: cidkidnix <cidkidnix@protonmail.com>
Co-authored-by: Dylan Green <67574902+cidkidnix@users.noreply.github.com>
Co-authored-by: John Ericson <git@JohnEricson.me>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

1 files changed, 7 insertions, 4 deletions

diff --git a/src/libstore/sqlite.cc b/src/libstore/sqlite.cc
index df334c23c..7c8decb74 100644
--- a/src/libstore/sqlite.cc
+++ b/src/libstore/sqlite.cc
@@ -1,6 +1,7 @@
 #include "sqlite.hh"
 #include "globals.hh"
 #include "util.hh"
+#include "url.hh"
 
 #include <sqlite3.h>
 
@@ -50,15 +51,17 @@ static void traceSQL(void * x, const char * sql)
     notice("SQL<[%1%]>", sql);
 };
 
-SQLite::SQLite(const Path & path, bool create)
+SQLite::SQLite(const Path & path, SQLiteOpenMode mode)
 {
     // useSQLiteWAL also indicates what virtual file system we need.  Using
     // `unix-dotfile` is needed on NFS file systems and on Windows' Subsystem
     // for Linux (WSL) where useSQLiteWAL should be false by default.
     const char *vfs = settings.useSQLiteWAL ? 0 : "unix-dotfile";
-    int flags = SQLITE_OPEN_READWRITE;
-    if (create) flags |= SQLITE_OPEN_CREATE;
-    int ret = sqlite3_open_v2(path.c_str(), &db, flags, vfs);
+    bool immutable = mode == SQLiteOpenMode::Immutable;
+    int flags = immutable ? SQLITE_OPEN_READONLY : SQLITE_OPEN_READWRITE;
+    if (mode == SQLiteOpenMode::Normal) flags |= SQLITE_OPEN_CREATE;
+    auto uri = "file:" + percentEncode(path) + "?immutable=" + (immutable ? "1" : "0");
+    int ret = sqlite3_open_v2(uri.c_str(), &db, SQLITE_OPEN_URI | flags, vfs);
     if (ret != SQLITE_OK) {
         const char * err = sqlite3_errstr(ret);
         throw Error("cannot open SQLite database '%s': %s", path, err);