From: Ralph Boehme <slow@samba.org>
Date: Sat, 1 Feb 2025 09:37:40 +0000 (+0100)
Subject: s3/brlock: add share_mode_do_locked_brl()
X-Git-Tag: samba-4.21.6~32
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0d06276060f7aebefdffb51342de57212e75e8b2;p=thirdparty%2Fsamba.git

s3/brlock: add share_mode_do_locked_brl()

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15767

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Ralph Boehme <slow@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
(cherry picked from commit e17fb732c89f8b34de00904383044de3c4f85bd0)
---

diff --git a/source3/locking/brlock.c b/source3/locking/brlock.c
index 51d9dc2e599..fcbce52f9c1 100644
--- a/source3/locking/brlock.c
+++ b/source3/locking/brlock.c
@@ -34,6 +34,7 @@
 #include "serverid.h"
 #include "messages.h"
 #include "util_tdb.h"
+#include "source3/locking/share_mode_lock.h"
 
 #undef DBGC_CLASS
 #define DBGC_CLASS DBGC_LOCKING
@@ -1927,3 +1928,105 @@ done:
 	talloc_free(frame);
 	return ret;
 }
+
+struct share_mode_do_locked_brl_state {
+	share_mode_do_locked_brl_fn_t cb;
+	void *cb_data;
+	struct files_struct *fsp;
+	NTSTATUS status;
+};
+
+static void share_mode_do_locked_brl_fn(struct share_mode_lock *lck,
+					void *private_data)
+{
+	struct share_mode_do_locked_brl_state *state = private_data;
+	struct byte_range_lock *br_lck = NULL;
+	TDB_DATA key = make_tdb_data((uint8_t *)&state->fsp->file_id,
+				     sizeof(state->fsp->file_id));
+
+	if (lp_locking(state->fsp->conn->params) &&
+	    state->fsp->fsp_flags.can_lock)
+	{
+		br_lck = brl_get_locks_readonly_parse(talloc_tos(),
+						      state->fsp);
+		if (br_lck == NULL) {
+			state->status = NT_STATUS_NO_MEMORY;
+			return;
+		}
+	}
+
+	state->cb(lck, br_lck, state->cb_data);
+
+	if (br_lck == NULL || !br_lck->modified) {
+		TALLOC_FREE(br_lck);
+		return;
+	}
+
+	br_lck->record = dbwrap_fetch_locked(brlock_db, br_lck, key);
+	if (br_lck->record == NULL) {
+		DBG_ERR("Could not lock byte range lock entry for '%s'\n",
+			fsp_str_dbg(state->fsp));
+		TALLOC_FREE(br_lck);
+		state->status = NT_STATUS_INTERNAL_DB_ERROR;
+		return;
+	}
+
+	byte_range_lock_flush(br_lck);
+	share_mode_wakeup_waiters(br_lck->fsp->file_id);
+	TALLOC_FREE(br_lck);
+}
+
+/*
+ * Run cb with a glock'ed locking.tdb record, providing both a share_mode_lock
+ * and a br_lck object. An initial read-only, but upgradable, br_lck object is
+ * fetched from brlock.tdb while holding the glock on the locking.tdb record.
+ *
+ * This function only ever hold one low-level TDB chainlock at a time on either
+ * locking.tdb or brlock.tdb, so it can't run afoul any lock order violations.
+ *
+ * Note that br_lck argument in the callback might be NULL in case lp_locking()
+ * is disabled, the fsp doesn't allow locking or is a directory, so either
+ * the caller or the callback have to check for this.
+ */
+NTSTATUS share_mode_do_locked_brl(files_struct *fsp,
+				  share_mode_do_locked_brl_fn_t cb,
+				  void *cb_data)
+{
+	static bool recursion_guard;
+	TALLOC_CTX *frame = NULL;
+	struct share_mode_do_locked_brl_state state = {
+		.fsp = fsp,
+		.cb = cb,
+		.cb_data = cb_data,
+	};
+	NTSTATUS status;
+
+	SMB_ASSERT(!recursion_guard);
+
+	/* silently return ok on print files as we don't do locking there */
+	if (fsp->print_file) {
+		return NT_STATUS_OK;
+	}
+
+	frame = talloc_stackframe();
+
+	recursion_guard = true;
+	status = share_mode_do_locked_vfs_allowed(
+					fsp->file_id,
+					share_mode_do_locked_brl_fn,
+					&state);
+	recursion_guard = false;
+	if (!NT_STATUS_IS_OK(status)) {
+		DBG_ERR("share_mode_do_locked_vfs_allowed() failed for %s - %s\n",
+			fsp_str_dbg(fsp), nt_errstr(status));
+		TALLOC_FREE(frame);
+		return status;
+	}
+	if (!NT_STATUS_IS_OK(state.status)) {
+		TALLOC_FREE(frame);
+		return state.status;
+	}
+
+	TALLOC_FREE(frame);
+	return NT_STATUS_OK;
+}
diff --git a/source3/locking/proto.h b/source3/locking/proto.h
index 3413596baed..c9d769ba53f 100644
--- a/source3/locking/proto.h
+++ b/source3/locking/proto.h
@@ -87,6 +87,14 @@ struct byte_range_lock *brl_get_locks_for_locking(TALLOC_CTX *mem_ctx,
 						  files_struct *fsp,
 						  TALLOC_CTX *req_mem_ctx,
 						  const struct GUID *req_guid);
+struct share_mode_lock;
+typedef void (*share_mode_do_locked_brl_fn_t)(
+	struct share_mode_lock *lck,
+	struct byte_range_lock *br_lck, /* br_lck can be NULL */
+	void *private_data);
+NTSTATUS share_mode_do_locked_brl(files_struct *fsp,
+		 share_mode_do_locked_brl_fn_t fn,
+		 void *private_data);
 struct byte_range_lock *brl_get_locks(TALLOC_CTX *mem_ctx,
 					files_struct *fsp);
 struct byte_range_lock *brl_get_locks_readonly(files_struct *fsp);