[PATCH pve-cluster 04/10] pmxcfs: memdb: add change notification hook

[Hannes Laimer <h.laimer@proxmox.com>]

Every mutation of the cluster file system, local or delivered from
another node, passes through memdb, which makes it the one place where
a change notification can be raised for all of them. Add a hook the
daemon installs at startup and call it as the last step of a mutation,
after the change is persisted and the guest list updated. An observer
is then told only about changes that survived, and whatever it reads
next, the guest list included, already reflects them. A node that
takes the whole state from the cluster during a synchronization raises
a resync in place of the mutations it never saw, since its state is
replaced as a whole then.

The hook stays a plain function pointer rather than a direct call
into the notifier, since memdb is part of the static C library the
database tools and the unit tests also link, which must not drag the
socket server along. The event types come straight from the notifier's
header, so the values cross the boundary without translation.

Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
---
 src/pmxcfs/Makefile   |  1 +
 src/pmxcfs/database.c |  2 ++
 src/pmxcfs/memdb.c    | 24 ++++++++++++++++++++++++
 src/pmxcfs/memdb.h    | 11 +++++++++++
 4 files changed, 38 insertions(+)

diff --git a/src/pmxcfs/Makefile b/src/pmxcfs/Makefile
index 547f258..90bc6a5 100644
--- a/src/pmxcfs/Makefile
+++ b/src/pmxcfs/Makefile
@@ -8,6 +8,7 @@ CFLAGS += -Wpedantic
 CFLAGS += -g -O2
 CFLAGS += -I.
 CFLAGS += $(shell pkg-config --cflags $(DEPENDENCIES))
+CFLAGS += -I../rust/pmxcfs-ffi/include
 
 LDFLAGS += -Wl,-z,relro $(shell pkg-config --libs $(DEPENDENCIES))
 
diff --git a/src/pmxcfs/database.c b/src/pmxcfs/database.c
index 4ee2389..486fe84 100644
--- a/src/pmxcfs/database.c
+++ b/src/pmxcfs/database.c
@@ -611,6 +611,8 @@ gboolean bdb_backend_commit_update(
 
     memdb_update_locks(memdb);
 
+    memdb_notify(PMXCFS_NOTIFY_RESYNC, memdb->root->version, NULL, NULL);
+
     result = TRUE;
 
 ret:
diff --git a/src/pmxcfs/memdb.c b/src/pmxcfs/memdb.c
index 77d7652..a6a2a62 100644
--- a/src/pmxcfs/memdb.c
+++ b/src/pmxcfs/memdb.c
@@ -41,6 +41,18 @@
 
 #define CFS_LOCK_TIMEOUT (60 * 2)
 
+// Set once before any other thread runs, so no locking is needed here.
+// The hook runs under memdb->mutex and must not call back into memdb.
+static memdb_notify_fn notify_hook;
+
+void memdb_set_notify_hook(memdb_notify_fn hook) { notify_hook = hook; }
+
+void memdb_notify(enum pmxcfs_notify_type type, uint64_t seq, const char *path, const char *to) {
+    if (notify_hook) {
+        notify_hook(type, seq, path, to);
+    }
+}
+
 memdb_tree_entry_t *memdb_tree_entry_new(const char *name) {
     g_return_val_if_fail(name != NULL, NULL);
 
@@ -621,6 +633,8 @@ int memdb_mkdir(memdb_t *memdb, const char *path, guint32 writer, guint32 mtime)
         }
     }
 
+    memdb_notify(PMXCFS_NOTIFY_MKDIR, memdb->root->version, path, NULL);
+
     ret = 0;
 
 ret:
@@ -824,6 +838,10 @@ static int memdb_pwrite(
         vmlist_register_vm(vmtype, vmid, nodename);
     }
 
+    memdb_notify(
+        old ? PMXCFS_NOTIFY_WRITE : PMXCFS_NOTIFY_CREATE, memdb->root->version, path, NULL
+    );
+
     ret = count;
 
 ret:
@@ -929,6 +947,8 @@ int memdb_mtime(memdb_t *memdb, const char *path, guint32 writer, guint32 mtime)
         }
     }
 
+    memdb_notify(PMXCFS_NOTIFY_MTIME, memdb->root->version, path, NULL);
+
     ret = 0;
 
 ret:
@@ -1191,6 +1211,8 @@ int memdb_rename(memdb_t *memdb, const char *from, const char *to, guint32 write
         /* directories are alwayse empty (see unlink_tree_entry) */
     }
 
+    memdb_notify(PMXCFS_NOTIFY_RENAME, memdb->root->version, from, to);
+
     ret = 0;
 
 ret:
@@ -1264,6 +1286,8 @@ int memdb_delete(memdb_t *memdb, const char *path, guint32 writer, guint32 mtime
         vmlist_delete_vm(vmid);
     }
 
+    memdb_notify(PMXCFS_NOTIFY_DELETE, memdb->root->version, path, NULL);
+
     ret = 0;
 
 ret:
diff --git a/src/pmxcfs/memdb.h b/src/pmxcfs/memdb.h
index bca8967..f7dff5b 100644
--- a/src/pmxcfs/memdb.h
+++ b/src/pmxcfs/memdb.h
@@ -22,11 +22,14 @@
 #define _PVE_MEMDB_H_
 
 #include <stdio.h>
+#include <stdint.h>
 #include <stdlib.h>
 
 #include <glib.h>
 #include <sys/statvfs.h>
 
+#include "pmxcfs-notify.h"
+
 #define MEMDB_MAX_FILE_SIZE (1024 * 1024)    // 1 MiB
 #define MEMDB_MAX_FSSIZE (128 * 1024 * 1024) // 128 MiB
 #define MEMDB_MAX_INODES (256 * 1024)        // 256k
@@ -83,6 +86,10 @@ typedef struct {
     db_backend_t *bdb;
 } memdb_t;
 
+typedef void (*memdb_notify_fn)(
+    enum pmxcfs_notify_type type, uint64_t seq, const char *path, const char *to
+);
+
 memdb_t *memdb_open(const char *dbfilename);
 
 void memdb_close(memdb_t *memdb);
@@ -138,6 +145,10 @@ memdb_tree_entry_t *memdb_getattr(memdb_t *memdb, const char *path);
 
 int memdb_rename(memdb_t *memdb, const char *from, const char *to, guint32 writer, guint32 mtime);
 
+void memdb_set_notify_hook(memdb_notify_fn hook);
+
+void memdb_notify(enum pmxcfs_notify_type type, uint64_t seq, const char *path, const char *to);
+
 void memdb_dump(memdb_t *memdb);
 
 gboolean
-- 
2.47.3