util: ntdb_new() supports NTDB_CLEAR_IF_FIRST.

There are various issues with NTDB_CLEAR_IF_FIRST which makes it
better if we don't have to use it, but much of the code does, so
we fake up support here.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/lib/util/util_ntdb.c b/lib/util/util_ntdb.c
index 9c3e2a52549c292b0123bc255fabc4f7bf9c1d7e..10d60c2b84d3a29d99326948414125e10f0efcad 100644 (file)
--- a/lib/util/util_ntdb.c
+++ b/lib/util/util_ntdb.c
@@ -21,6 +21,81 @@
 #include "includes.h"
 #include "util_ntdb.h"
 #include "lib/param/param.h"
+#include "replace.h"
+#include "system/filesys.h"
+
+/*
+ * This handles NTDB_CLEAR_IF_FIRST.
+ *
+ * It's a bad idea for new code, but S3 uses it quite a bit.
+ */
+static enum NTDB_ERROR clear_if_first(int fd, void *unused)
+{
+       /* We hold a lock offset 4 always, so we can tell if anyone else is. */
+       struct flock fl;
+
+       fl.l_type = F_WRLCK;
+       fl.l_whence = SEEK_SET;
+       fl.l_start = 4; /* ACTIVE_LOCK */
+       fl.l_len = 1;
+
+       if (fcntl(fd, F_SETLK, &fl) == 0) {
+               /* We must be first ones to open it w/ NTDB_CLEAR_IF_FIRST! */
+               if (ftruncate(fd, 0) != 0) {
+                       return NTDB_ERR_IO;
+               }
+       }
+       fl.l_type = F_RDLCK;
+       if (fcntl(fd, F_SETLKW, &fl) != 0) {
+               return NTDB_ERR_IO;
+       }
+       return NTDB_SUCCESS;
+}
+
+/* We only need these for the CLEAR_IF_FIRST lock. */
+static int reacquire_cif_lock(struct ntdb_context *ntdb, bool *fail)
+{
+       struct flock fl;
+       union ntdb_attribute cif;
+
+       cif.openhook.base.attr = NTDB_ATTRIBUTE_OPENHOOK;
+       cif.openhook.base.next = NULL;
+
+       if (ntdb_get_attribute(ntdb, &cif) != NTDB_SUCCESS
+           || cif.openhook.fn != clear_if_first) {
+               return 0;
+       }
+
+       /* We hold a lock offset 4 always, so we can tell if anyone else is. */
+       fl.l_type = F_RDLCK;
+       fl.l_whence = SEEK_SET;
+       fl.l_start = 4; /* ACTIVE_LOCK */
+       fl.l_len = 1;
+       if (fcntl(ntdb_fd(ntdb), F_SETLKW, &fl) != 0) {
+               *fail = true;
+               return -1;
+       }
+       return 0;
+}
+
+/* You only need this on databases with NTDB_CLEAR_IF_FIRST */
+int ntdb_reopen(struct ntdb_context *ntdb)
+{
+       bool unused;
+       return reacquire_cif_lock(ntdb, &unused);
+}
+
+/* You only need to do this if you have NTDB_CLEAR_IF_FIRST databases, and
+ * the parent will go away before this child. */
+int ntdb_reopen_all(void)
+{
+       bool fail = false;
+
+       ntdb_foreach(reacquire_cif_lock, &fail);
+       if (fail)
+               return -1;
+       return 0;
+}
 
 static void *ntdb_talloc(const void *owner, size_t len, void *priv_data)
 {
@@ -74,7 +149,7 @@ struct ntdb_context *ntdb_new(TALLOC_CTX *ctx,
                              union ntdb_attribute *attr,
                              struct loadparm_context *lp_ctx)
 {
-       union ntdb_attribute log_attr, alloc_attr;
+       union ntdb_attribute log_attr, alloc_attr, open_attr;
        struct ntdb_context *ntdb;
 
        if (lp_ctx && !lpcfg_use_mmap(lp_ctx)) {
@@ -96,6 +171,14 @@ struct ntdb_context *ntdb_new(TALLOC_CTX *ctx,
        alloc_attr.alloc.expand = ntdb_expand;
        alloc_attr.alloc.free = ntdb_free;
 
+       if (ntdb_flags & NTDB_CLEAR_IF_FIRST) {
+               log_attr.base.next = &open_attr;
+               open_attr.openhook.base.attr = NTDB_ATTRIBUTE_OPENHOOK;
+               open_attr.openhook.base.next = attr;
+               open_attr.openhook.fn = clear_if_first;
+               ntdb_flags &= ~NTDB_CLEAR_IF_FIRST;
+       }
+
        ntdb = ntdb_open(name, ntdb_flags, open_flags, mode, &alloc_attr);
        if (!ntdb) {
                return NULL;

diff --git a/lib/util/util_ntdb.h b/lib/util/util_ntdb.h
index a5eab7f436d031a0fcacf55caa397d0bbfe4a079..d65d8b6f7bbf6b12e31862e0d9b39087a225a7b2 100644 (file)
--- a/lib/util/util_ntdb.h
+++ b/lib/util/util_ntdb.h
@@ -27,6 +27,21 @@
 struct loadparm_context;
 union ntdb_attribute;
 
+
+/* You only need this on databases with NTDB_CLEAR_IF_FIRST */
+int ntdb_reopen(struct ntdb_context *ntdb);
+
+/* You only need to do this if you have NTDB_CLEAR_IF_FIRST databases, and
+ * the parent will go away before this child. */
+int ntdb_reopen_all(void);
+
+/*
+ * This is like TDB_CLEAR_IF_FIRST, for use with ntdb_new.
+ *
+ * It's a bad idea for new code.
+ */
+#define NTDB_CLEAR_IF_FIRST 1048576
+
 /***************************************************************
  Open an NTDB using talloc: it will be allocated off the context, and
  all NTDB_DATA.dptr are allocated as children of the ntdb context.