sql: Small documentation improvements for SandboxedVfs.
Change-Id: I472582eaea658d2ee8a4c157a0161611d2aca2e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359229
Reviewed-by: Ken Rockot <[email protected]>
Commit-Queue: Ken Rockot <[email protected]>
Auto-Submit: Victor Costan <[email protected]>
Cr-Commit-Position: refs/heads/master@{#798727}
diff --git a/sql/sandboxed_vfs_file.cc b/sql/sandboxed_vfs_file.cc
index 26d144e..afaee54 100644
--- a/sql/sandboxed_vfs_file.cc
+++ b/sql/sandboxed_vfs_file.cc
@@ -215,8 +215,8 @@
if (file_.SetLength(size))
return SQLITE_OK;
- // On Mac, the default sandbox blocks ftruncate(), so we have to use a sync
- // mojo IPC to ask the browser process to call ftruncate() for us.
+ // On macOS < 10.15, the default sandbox blocks ftruncate(), so we have to use
+ // a sync mojo IPC to ask the browser process to call ftruncate() for us.
//
// TODO(crbug.com/1084565): Figure out if we can allow ftruncate() in renderer
// and utility processes. It would be useful for low-level storage APIs, like
@@ -466,7 +466,13 @@
DCHECK_GE(page_size, 0);
DCHECK(result);
- // NOTE: This would be needed by SQLite's WAL mode.
+ // https://www.sqlite.org/wal.html#use_of_wal_without_shared_memory states
+ // that SQLite only attempts to use shared memory "-shm" files for databases
+ // in WAL mode that may be accessed by multiple processes (are not EXCLUSIVE).
+ //
+ // Chrome will not only use WAL mode on EXCLUSIVE databases.
+ NOTREACHED() << "SQLite should not attempt to use shared memory";
+
*result = nullptr;
return SQLITE_IOERR;
}
@@ -475,18 +481,37 @@
DCHECK_GE(offset, 0);
DCHECK_GE(size, 0);
- // NOTE: This would be needed by SQLite's WAL mode.
+ // https://www.sqlite.org/wal.html#use_of_wal_without_shared_memory states
+ // that SQLite only attempts to use shared memory "-shm" files for databases
+ // in WAL mode that may be accessed by multiple processes (are not EXCLUSIVE).
+ //
+ // Chrome will not only use WAL mode on EXCLUSIVE databases.
+ NOTREACHED() << "SQLite should not attempt to use shared memory";
+
return SQLITE_IOERR;
}
void SandboxedVfsFile::ShmBarrier() {
+ // https://www.sqlite.org/wal.html#use_of_wal_without_shared_memory states
+ // that SQLite only attempts to use shared memory "-shm" files for databases
+ // in WAL mode that may be accessed by multiple processes (are not EXCLUSIVE).
+ //
+ // Chrome will not only use WAL mode on EXCLUSIVE databases.
+ NOTREACHED() << "SQLite should not attempt to use shared memory";
+
// All writes to shared memory that have already been issued before this
// function is called must complete before the function returns.
std::atomic_thread_fence(std::memory_order_acq_rel);
}
int SandboxedVfsFile::ShmUnmap(int also_delete_file) {
- // NOTE: This would be needed by SQLite's WAL mode.
+ // https://www.sqlite.org/wal.html#use_of_wal_without_shared_memory states
+ // that SQLite only attempts to use shared memory "-shm" files for databases
+ // in WAL mode that may be accessed by multiple processes (are not EXCLUSIVE).
+ //
+ // Chrome will not only use WAL mode on EXCLUSIVE databases.
+ NOTREACHED() << "SQLite should not attempt to use shared memory";
+
return SQLITE_IOERR;
}
